Rewrite engine threading (#697)

* Create orchestrator, replacing Step class

* Rewrite tests, improve test tools

* Fix integration tests

cameraview/build.gradle

@@ -17,7 +17,7 @@ android {
         versionCode 1
         versionName project.version
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
-        testInstrumentationRunnerArgument "filter", "com.otaliastudios.cameraview.runner.SdkExcludeFilter"
+        testInstrumentationRunnerArgument "filter", "com.otaliastudios.cameraview.tools.SdkExcludeFilter"
     }
 
     buildTypes {
@@ -42,8 +42,8 @@ dependencies {
     androidTestImplementation 'org.mockito:mockito-android:2.28.2'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
 
-    api 'androidx.exifinterface:exifinterface:1.0.0'
+    api 'androidx.exifinterface:exifinterface:1.1.0'
-    api 'androidx.lifecycle:lifecycle-common:2.1.0-alpha01'
+    api 'androidx.lifecycle:lifecycle-common:2.1.0'
     api 'com.google.android.gms:play-services-tasks:17.0.0'
     implementation 'androidx.annotation:annotation:1.1.0'
 }
@@ -250,6 +250,7 @@ task mergeCoverageReports(type: JacocoReport) {
         classFilter.add('**/com/otaliastudios/cameraview/picture/**.*')
         classFilter.add('**/com/otaliastudios/cameraview/video/**.*')
         // TODO these below could be easily testable ALSO outside of the integration tests
+        classFilter.add('**/com/otaliastudios/cameraview/orchestrator/**.*')
         classFilter.add('**/com/otaliastudios/cameraview/video/encoding/**.*')
     }
     // We don't test OpenGL filters.

cameraview/src/androidTest/java/com/otaliastudios/cameraview/BaseTest.java

@@ -11,7 +11,7 @@ import android.os.PowerManager;
 import androidx.annotation.NonNull;
 import androidx.test.platform.app.InstrumentationRegistry;
 
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 
 import org.junit.After;
 import org.junit.AfterClass;
@@ -103,7 +103,7 @@ public class BaseTest {
     }
 
     @NonNull
-    protected static Stubber doCountDown(final CountDownLatch latch) {
+    protected static Stubber doCountDown(@NonNull final CountDownLatch latch) {
         return doAnswer(new Answer<Object>() {
             @Override
             public Object answer(InvocationOnMock invocation) {
@@ -118,7 +118,7 @@ public class BaseTest {
         return doAnswer(new Answer<Object>() {
             @Override
             public Object answer(InvocationOnMock invocation) {
-                op.end(response);
+                op.controller().end(response);
                 return null;
             }
         });
@@ -126,14 +126,6 @@ public class BaseTest {
 
     @NonNull
     protected static <T> Stubber doEndOp(final Op<T> op, final int withReturnArgument) {
-        return doAnswer(new Answer<Object>() {
+        return op.controller().from(withReturnArgument);
-            @Override
-            public Object answer(InvocationOnMock invocation) {
-                //noinspection unchecked
-                T o = (T) invocation.getArguments()[withReturnArgument];
-                op.end(o);
-                return null;
-            }
-        });
     }
 }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraLoggerTest.java

@@ -1,7 +1,7 @@
 package com.otaliastudios.cameraview;
 
 
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
@@ -109,7 +109,7 @@ public class CameraLoggerTest extends BaseTest {
         CameraLogger.Logger mock = mock(CameraLogger.Logger.class);
         CameraLogger.registerLogger(mock);
 
-        final Op<Throwable> op = new Op<>();
+        final Op<Throwable> op = new Op<>(false);
         doEndOp(op, 3)
                 .when(mock)
                 .log(anyInt(), anyString(), anyString(), any(Throwable.class));

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraUtilsTest.java

@@ -6,11 +6,10 @@ import android.content.pm.PackageManager;
 import android.graphics.Bitmap;
 import android.graphics.Color;
 
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import androidx.test.annotation.UiThreadTest;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
 
@@ -20,7 +19,6 @@ import org.junit.runner.RunWith;
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.charset.Charset;
 
@@ -51,21 +49,21 @@ public class CameraUtilsTest extends BaseTest {
     private Op<String> writeAndReadString(@NonNull String data) {
         final File file = new File(getContext().getFilesDir(), "string.txt");
         final byte[] bytes = data.getBytes(Charset.forName("UTF-8"));
-        final Op<String> result = new Op<>(true);
+        final Op<String> result = new Op<>();
         final FileCallback callback = new FileCallback() {
             @Override
             public void onFileReady(@Nullable File file) {
                 if (file == null) {
-                    result.end(null);
+                    result.controller().end(null);
                 } else {
                     // Read back the file.
                     try {
                         FileInputStream stream = new FileInputStream(file);
                         byte[] bytes = new byte[stream.available()];
                         stream.read(bytes);
-                        result.end(new String(bytes, Charset.forName("UTF-8")));
+                        result.controller().end(new String(bytes, Charset.forName("UTF-8")));
                     } catch (IOException e) {
-                        result.end(null);
+                        result.controller().end(null);
                     }
                 }
             }
@@ -94,12 +92,12 @@ public class CameraUtilsTest extends BaseTest {
         source.compress(Bitmap.CompressFormat.PNG, 100, os);
         final byte[] data = os.toByteArray();
 
-        final Op<Bitmap> decode = new Op<>(true);
+        final Op<Bitmap> decode = new Op<>();
         if (async) {
             final BitmapCallback callback = new BitmapCallback() {
                 @Override
                 public void onBitmapReady(Bitmap bitmap) {
-                    decode.end(bitmap);
+                    decode.controller().end(bitmap);
                 }
             };
 
@@ -121,7 +119,7 @@ public class CameraUtilsTest extends BaseTest {
             } else {
                 result = CameraUtils.decodeBitmap(data);
             }
-            decode.end(result);
+            decode.controller().end(result);
         }
         return decode;
     }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraViewCallbacksTest.java

@@ -17,7 +17,7 @@ import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameProcessor;
 import com.otaliastudios.cameraview.gesture.Gesture;
 import com.otaliastudios.cameraview.gesture.GestureAction;
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 import com.otaliastudios.cameraview.engine.MockCameraEngine;
 import com.otaliastudios.cameraview.markers.AutoFocusMarker;
 import com.otaliastudios.cameraview.markers.AutoFocusTrigger;
@@ -90,7 +90,7 @@ public class CameraViewCallbacksTest extends BaseTest {
                 camera.doInstantiatePreview();
                 camera.addCameraListener(listener);
                 camera.addFrameProcessor(processor);
-                op = new Op<>(true);
+                op = new Op<>();
             }
         });
     }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/CameraViewTest.java

@@ -23,9 +23,9 @@ import com.otaliastudios.cameraview.controls.Flash;
 import com.otaliastudios.cameraview.controls.PictureFormat;
 import com.otaliastudios.cameraview.controls.Preview;
 import com.otaliastudios.cameraview.engine.CameraEngine;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.filter.Filter;
 import com.otaliastudios.cameraview.filter.Filters;
-import com.otaliastudios.cameraview.filter.NoFilter;
 import com.otaliastudios.cameraview.filters.DuotoneFilter;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameProcessor;
@@ -41,7 +41,7 @@ import com.otaliastudios.cameraview.gesture.PinchGestureFinder;
 import com.otaliastudios.cameraview.gesture.ScrollGestureFinder;
 import com.otaliastudios.cameraview.gesture.TapGestureFinder;
 import com.otaliastudios.cameraview.engine.MockCameraEngine;
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 import com.otaliastudios.cameraview.markers.AutoFocusMarker;
 import com.otaliastudios.cameraview.markers.DefaultAutoFocusMarker;
 import com.otaliastudios.cameraview.markers.MarkerLayout;
@@ -128,7 +128,7 @@ public class CameraViewTest extends BaseTest {
     public void testClose() {
         cameraView.close();
         verify(mockPreview, times(1)).onPause();
-        verify(mockController, times(1)).stop();
+        verify(mockController, times(1)).stop(false);
     }
 
     @Test
@@ -239,7 +239,7 @@ public class CameraViewTest extends BaseTest {
     public void testGestureAction_capture() {
         CameraOptions o = mock(CameraOptions.class);
         mockController.setMockCameraOptions(o);
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         MotionEvent event = MotionEvent.obtain(0L, 0L, 0, 0f, 0f, 0);
         uiSync(new Runnable() {
             @Override
@@ -261,7 +261,7 @@ public class CameraViewTest extends BaseTest {
     public void testGestureAction_focus() {
         CameraOptions o = mock(CameraOptions.class);
         mockController.setMockCameraOptions(o);
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         MotionEvent event = MotionEvent.obtain(0L, 0L, 0, 0f, 0f, 0);
         uiSync(new Runnable() {
             @Override
@@ -286,7 +286,7 @@ public class CameraViewTest extends BaseTest {
     public void testGestureAction_zoom() {
         CameraOptions o = mock(CameraOptions.class);
         mockController.setMockCameraOptions(o);
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         mockController.mZoomChanged = false;
         MotionEvent event = MotionEvent.obtain(0L, 0L, 0, 0f, 0f, 0);
         final FactorHolder factor = new FactorHolder();
@@ -327,7 +327,7 @@ public class CameraViewTest extends BaseTest {
         o.exposureCorrectionMaxValue = 10F;
         o.exposureCorrectionMinValue = -10F;
         mockController.setMockCameraOptions(o);
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         mockController.mExposureCorrectionChanged = false;
         MotionEvent event = MotionEvent.obtain(0L, 0L, 0, 0f, 0f, 0);
         final FactorHolder factor = new FactorHolder();
@@ -363,7 +363,7 @@ public class CameraViewTest extends BaseTest {
 
     @Test
     public void testGestureAction_filterControl1() {
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         mockController.setMockCameraOptions(mock(CameraOptions.class));
         DuotoneFilter filter = new DuotoneFilter(); // supports two parameters
         filter.setParameter1(0F);
@@ -405,7 +405,7 @@ public class CameraViewTest extends BaseTest {
 
     @Test
     public void testGestureAction_filterControl2() {
-        mockController.setMockEngineState(true);
+        mockController.setMockState(CameraState.PREVIEW);
         mockController.setMockCameraOptions(mock(CameraOptions.class));
         DuotoneFilter filter = new DuotoneFilter(); // supports two parameters
         filter.setParameter2(0F);
@@ -891,7 +891,7 @@ public class CameraViewTest extends BaseTest {
         cameraView.mMarkerLayout = markerLayout;
         final PointF point = new PointF(0, 0);
         final PointF[] points = new PointF[]{ point };
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         doEndOp(op, true).when(markerLayout).onEvent(MarkerLayout.TYPE_AUTOFOCUS, points);
         cameraView.mCameraCallbacks.dispatchOnFocusStart(Gesture.TAP, point);
         assertNotNull(op.await(100));

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/Camera1IntegrationTest.java

@@ -2,6 +2,7 @@ package com.otaliastudios.cameraview.engine;
 
 import com.otaliastudios.cameraview.controls.Engine;
 
+import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import androidx.annotation.NonNull;

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/CameraIntegrationTest.java

@@ -25,9 +25,10 @@ import com.otaliastudios.cameraview.controls.Hdr;
 import com.otaliastudios.cameraview.controls.Mode;
 import com.otaliastudios.cameraview.controls.PictureFormat;
 import com.otaliastudios.cameraview.controls.WhiteBalance;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameProcessor;
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 import com.otaliastudios.cameraview.internal.utils.WorkerHandler;
 import com.otaliastudios.cameraview.overlay.Overlay;
 import com.otaliastudios.cameraview.size.Size;
@@ -110,12 +111,12 @@ public abstract class CameraIntegrationTest extends BaseTest {
                 // Ensure that controller exceptions are thrown on this thread (not on the UI thread).
                 // TODO this makes debugging for wrong tests very hard, as we don't get the exception
                 // unless waitForUiException() is called.
-                uiExceptionOp = new Op<>(true);
+                uiExceptionOp = new Op<>();
                 WorkerHandler crashThread = WorkerHandler.get("CrashThread");
                 crashThread.getThread().setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
                     @Override
                     public void uncaughtException(Thread t, Throwable e) {
-                        uiExceptionOp.end(e);
+                        uiExceptionOp.controller().end(e);
                     }
                 });
                 controller.mCrashHandler = crashThread.getHandler();
@@ -139,7 +140,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
 
     private CameraOptions openSync(boolean expectSuccess) {
         camera.open();
-        final Op<CameraOptions> open = new Op<>(true);
+        final Op<CameraOptions> open = new Op<>();
         doEndOp(open, 0).when(listener).onCameraOpened(any(CameraOptions.class));
         CameraOptions result = open.await(DELAY);
         if (expectSuccess) {
@@ -156,13 +157,12 @@ public abstract class CameraIntegrationTest extends BaseTest {
         // Extra wait for the bind and preview state, so we run tests in a fully operational
         // state. If we didn't do so, we could have null values, for example, in getPictureSize
         // or in getSnapshotSize.
-        while (controller.getBindState() != CameraEngine.STATE_STARTED) {}
+        while (controller.getState() != CameraState.PREVIEW) {}
-        while (controller.getPreviewState() != CameraEngine.STATE_STARTED) {}
     }
 
     private void closeSync(boolean expectSuccess) {
         camera.close();
-        final Op<Boolean> close = new Op<>(true);
+        final Op<Boolean> close = new Op<>();
         doEndOp(close, true).when(listener).onCameraClosed();
         Boolean result = close.await(DELAY);
         if (expectSuccess) {
@@ -180,7 +180,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
         doCountDown(onVideoRecordingEnd).when(listener).onVideoRecordingEnd();
 
         // Op for onVideoTaken.
-        final Op<VideoResult> video = new Op<>(true);
+        final Op<VideoResult> video = new Op<>();
         doEndOp(video, 0).when(listener).onVideoTaken(any(VideoResult.class));
         doEndOp(video, null).when(listener).onCameraError(argThat(new ArgumentMatcher<CameraException>() {
             @Override
@@ -218,7 +218,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
 
     @Nullable
     private PictureResult waitForPictureResult(boolean expectSuccess) {
-        final Op<PictureResult> pic = new Op<>(true);
+        final Op<PictureResult> pic = new Op<>();
         doEndOp(pic, 0).when(listener).onPictureTaken(any(PictureResult.class));
         doEndOp(pic, null).when(listener).onCameraError(argThat(new ArgumentMatcher<CameraException>() {
             @Override
@@ -240,7 +240,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
     }
 
     private void takeVideoSync(boolean expectSuccess, int duration) {
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         doEndOp(op, true).when(listener).onVideoRecordingStart();
         doEndOp(op, false).when(listener).onCameraError(argThat(new ArgumentMatcher<CameraException>() {
             @Override
@@ -269,7 +269,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
     }
 
     private void takeVideoSnapshotSync(boolean expectSuccess, int duration) {
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         doEndOp(op, true).when(listener).onVideoRecordingStart();
         doEndOp(op, false).when(listener).onCameraError(argThat(new ArgumentMatcher<CameraException>() {
             @Override
@@ -296,14 +296,11 @@ public abstract class CameraIntegrationTest extends BaseTest {
 
     @Test
     public void testOpenClose() {
-        // Starting and stopping are hard to get since they happen on another thread.
+        assertEquals(controller.getState(), CameraState.OFF);
-        assertEquals(controller.getEngineState(), CameraEngine.STATE_STOPPED);
-
         openSync(true);
-        assertEquals(controller.getEngineState(), CameraEngine.STATE_STARTED);
+        assertTrue(controller.getState().isAtLeast(CameraState.ENGINE));
-
         closeSync(true);
-        assertEquals(controller.getEngineState(), CameraEngine.STATE_STOPPED);
+        assertEquals(controller.getState(), CameraState.OFF);
     }
 
     @Test
@@ -389,12 +386,11 @@ public abstract class CameraIntegrationTest extends BaseTest {
     @Test
     public void testSetZoom() {
         CameraOptions options = openSync(true);
-
-        controller.mZoomOp.listen();
         float oldValue = camera.getZoom();
         float newValue = 0.65f;
         camera.setZoom(newValue);
-        controller.mZoomOp.await(500);
+        Op<Void> op = new Op<>(controller.mZoomTask);
+        op.await(500);
 
         if (options.isZoomSupported()) {
             assertEquals(newValue, camera.getZoom(), 0f);
@@ -406,12 +402,11 @@ public abstract class CameraIntegrationTest extends BaseTest {
     @Test
     public void testSetExposureCorrection() {
         CameraOptions options = openSync(true);
-
-        controller.mExposureCorrectionOp.listen();
         float oldValue = camera.getExposureCorrection();
         float newValue = options.getExposureCorrectionMaxValue();
         camera.setExposureCorrection(newValue);
-        controller.mExposureCorrectionOp.await(300);
+        Op<Void> op = new Op<>(controller.mExposureCorrectionTask);
+        op.await(300);
 
         if (options.isExposureCorrectionSupported()) {
             assertEquals(newValue, camera.getExposureCorrection(), 0f);
@@ -426,9 +421,10 @@ public abstract class CameraIntegrationTest extends BaseTest {
         Flash[] values = Flash.values();
         Flash oldValue = camera.getFlash();
         for (Flash value : values) {
-            controller.mFlashOp.listen();
+
             camera.setFlash(value);
-            controller.mFlashOp.await(300);
+            Op<Void> op = new Op<>(controller.mFlashTask);
+            op.await(300);
             if (options.supports(value)) {
                 assertEquals(camera.getFlash(), value);
                 oldValue = value;
@@ -444,9 +440,9 @@ public abstract class CameraIntegrationTest extends BaseTest {
         WhiteBalance[] values = WhiteBalance.values();
         WhiteBalance oldValue = camera.getWhiteBalance();
         for (WhiteBalance value : values) {
-            controller.mWhiteBalanceOp.listen();
             camera.setWhiteBalance(value);
-            controller.mWhiteBalanceOp.await(300);
+            Op<Void> op = new Op<>(controller.mWhiteBalanceTask);
+            op.await(300);
             if (options.supports(value)) {
                 assertEquals(camera.getWhiteBalance(), value);
                 oldValue = value;
@@ -462,9 +458,9 @@ public abstract class CameraIntegrationTest extends BaseTest {
         Hdr[] values = Hdr.values();
         Hdr oldValue = camera.getHdr();
         for (Hdr value : values) {
-            controller.mHdrOp.listen();
             camera.setHdr(value);
-            controller.mHdrOp.await(300);
+            Op<Void> op = new Op<>(controller.mHdrTask);
+            op.await(300);
             if (options.supports(value)) {
                 assertEquals(camera.getHdr(), value);
                 oldValue = value;
@@ -487,9 +483,9 @@ public abstract class CameraIntegrationTest extends BaseTest {
     @Test
     public void testSetLocation() {
         openSync(true);
-        controller.mLocationOp.listen();
         camera.setLocation(10d, 2d);
-        controller.mLocationOp.await(300);
+        Op<Void> op = new Op<>(controller.mLocationTask);
+        op.await(300);
         assertNotNull(camera.getLocation());
         assertEquals(camera.getLocation().getLatitude(), 10d, 0d);
         assertEquals(camera.getLocation().getLongitude(), 2d, 0d);
@@ -499,19 +495,19 @@ public abstract class CameraIntegrationTest extends BaseTest {
     @Test
     public void testSetPreviewFrameRate() {
         openSync(true);
-        controller.mPreviewFrameRateOp.listen();
         camera.setPreviewFrameRate(30);
-        controller.mPreviewFrameRateOp.await(300);
+        Op<Void> op = new Op<>(controller.mPreviewFrameRateTask);
+        op.await(300);
         assertEquals(camera.getPreviewFrameRate(), 30, 0);
     }
 
     @Test
     public void testSetPlaySounds() {
-        controller.mPlaySoundsOp.listen();
         boolean oldValue = camera.getPlaySounds();
         boolean newValue = !oldValue;
         camera.setPlaySounds(newValue);
-        controller.mPlaySoundsOp.await(300);
+        Op<Void> op = new Op<>(controller.mPlaySoundsTask);
+        op.await(300);
 
         if (controller instanceof Camera1Engine) {
             Camera1Engine camera1Engine = (Camera1Engine) controller;
@@ -647,7 +643,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
     public void testStartAutoFocus() {
         CameraOptions o = openSync(true);
 
-        final Op<PointF> focus = new Op<>(true);
+        final Op<PointF> focus = new Op<>();
         doEndOp(focus, 0).when(listener).onAutoFocusStart(any(PointF.class));
 
         camera.startAutoFocus(1, 1);
@@ -664,7 +660,7 @@ public abstract class CameraIntegrationTest extends BaseTest {
     public void testStopAutoFocus() {
         CameraOptions o = openSync(true);
 
-        final Op<PointF> focus = new Op<>(true);
+        final Op<PointF> focus = new Op<>();
         doEndOp(focus, 1).when(listener).onAutoFocusEnd(anyBoolean(), any(PointF.class));
 
         camera.startAutoFocus(1, 1);
@@ -809,25 +805,24 @@ public abstract class CameraIntegrationTest extends BaseTest {
 
     //region Picture Formats
 
-    // TODO this fails because setPictureFormat triggers a restart() and takePicture can be called
+    @SuppressWarnings("ConstantConditions")
-    // in the middle of the restart, failing because the engine is not properly set up. To fix this
+    @Test
-    // we would have to change the whole CameraEngine threading scheme.
-    // @Test
     public void testPictureFormat_DNG() {
         openSync(true);
         if (camera.getCameraOptions().supports(PictureFormat.DNG)) {
+            Op<Boolean> op = new Op<>();
+            doEndOp(op, true).when(listener).onCameraOpened(any(CameraOptions.class));
             camera.setPictureFormat(PictureFormat.DNG);
+            assertNotNull(op.await(2000));
             camera.takePicture();
             PictureResult result = waitForPictureResult(true);
             // assert that result.getData() is a DNG file:
             // We can use the first 4 bytes assuming they are the same as a TIFF file
-            // https://en.wikipedia.org/wiki/List_of_file_signatures
+            // https://en.wikipedia.org/wiki/List_of_file_signatures 73, 73, 42, 0
             byte[] b = result.getData();
-            boolean isII = b[0] == 'I' && b[1] == 'I' && b[2] == '*' && b[3] == '.';
+            boolean isII = b[0] == 'I' && b[1] == 'I' && b[2] == '*' && b[3] == 0;
-            boolean isMM = b[0] == 'M' && b[1] == 'M' && b[2] == '.' && b[3] == '*';
+            boolean isMM = b[0] == 'M' && b[1] == 'M' && b[2] == 0 && b[3] == '*';
-            if (!isII && !isMM) {
+            assertTrue(isII || isMM);
-                throw new RuntimeException("Not a DNG file.");
-            }
         }
     }
 

cameraview/src/androidTest/java/com/otaliastudios/cameraview/engine/MockCameraEngine.java

@@ -12,6 +12,7 @@ import com.otaliastudios.cameraview.VideoResult;
 import com.otaliastudios.cameraview.controls.Facing;
 import com.otaliastudios.cameraview.controls.Flash;
 import com.otaliastudios.cameraview.controls.PictureFormat;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.frame.FrameManager;
 import com.otaliastudios.cameraview.gesture.Gesture;
 import com.otaliastudios.cameraview.controls.Hdr;
@@ -24,6 +25,7 @@ import androidx.annotation.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.Callable;
 
 public class MockCameraEngine extends CameraEngine {
 
@@ -80,8 +82,19 @@ public class MockCameraEngine extends CameraEngine {
         mPreviewStreamSize = size;
     }
 
-    public void setMockEngineState(boolean started) {
+    public void setMockState(@NonNull CameraState state) {
-        mEngineStep.setState(started ? STATE_STARTED : STATE_STOPPED);
+        Task<Void> change = mOrchestrator.scheduleStateChange(getState(),
+                state,
+                false,
+                new Callable<Task<Void>>() {
+            @Override
+            public Task<Void> call() {
+                return Tasks.forResult(null);
+            }
+        });
+        try {
+            Tasks.await(change);
+        } catch (Exception ignore) {}
     }
 
     @Override

cameraview/src/androidTest/java/com/otaliastudios/cameraview/gesture/GestureFinderTest.java

@@ -15,7 +15,7 @@ import android.widget.FrameLayout;
 
 import com.otaliastudios.cameraview.BaseTest;
 import com.otaliastudios.cameraview.TestActivity;
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 
 import org.hamcrest.Matchers;
 import org.junit.Before;
@@ -49,12 +49,12 @@ public abstract class GestureFinderTest<T extends GestureFinder> extends BaseTes
                 finder.setActive(true);
                 a.inflate(layout);
 
-                touchOp = new Op<>();
+                touchOp = new Op<>(false);
                 layout.setOnTouchListener(new View.OnTouchListener() {
                     @Override
                     public boolean onTouch(View view, MotionEvent motionEvent) {
                         boolean found = finder.onTouchEvent(motionEvent);
-                        if (found) touchOp.end(finder.getGesture());
+                        if (found) touchOp.controller().end(finder.getGesture());
                         return true;
                     }
                 });

cameraview/src/androidTest/java/com/otaliastudios/cameraview/gesture/PinchGestureFinderTest.java

@@ -6,7 +6,7 @@ import androidx.test.espresso.ViewAction;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
 
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -52,7 +52,7 @@ public class PinchGestureFinderTest extends GestureFinderTest<PinchGestureFinder
 
     private void testPinch(ViewAction action, boolean increasing) {
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         onLayout().perform(action);
         Gesture found = touchOp.await(10000);
         assertNotNull(found);

cameraview/src/androidTest/java/com/otaliastudios/cameraview/gesture/ScrollGestureFinderTest.java

@@ -6,7 +6,7 @@ import androidx.test.espresso.ViewAction;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.SmallTest;
 
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -49,7 +49,7 @@ public class ScrollGestureFinderTest extends GestureFinderTest<ScrollGestureFind
     public void testScrollDisabled() {
         finder.setActive(false);
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         onLayout().perform(swipeUp());
         Gesture found = touchOp.await(WAIT);
         assertNull(found);
@@ -57,7 +57,7 @@ public class ScrollGestureFinderTest extends GestureFinderTest<ScrollGestureFind
 
     private void testScroll(ViewAction scroll, Gesture expected, boolean increasing) {
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         onLayout().perform(scroll);
         Gesture found = touchOp.await(WAIT);
         assertEquals(found, expected);

cameraview/src/androidTest/java/com/otaliastudios/cameraview/gesture/TapGestureFinderTest.java

@@ -11,7 +11,7 @@ import androidx.test.filters.SmallTest;
 import android.view.InputDevice;
 import android.view.MotionEvent;
 
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 import com.otaliastudios.cameraview.size.Size;
 
 import org.junit.Test;
@@ -45,7 +45,7 @@ public class TapGestureFinderTest extends GestureFinderTest<TapGestureFinder> {
     @Test
     public void testTap() {
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         GeneralClickAction a = new GeneralClickAction(
                 Tap.SINGLE, GeneralLocation.CENTER, Press.FINGER,
                 InputDevice.SOURCE_UNKNOWN, MotionEvent.BUTTON_PRIMARY);
@@ -62,7 +62,7 @@ public class TapGestureFinderTest extends GestureFinderTest<TapGestureFinder> {
     public void testTapWhileDisabled() {
         finder.setActive(false);
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         onLayout().perform(click());
         Gesture found = touchOp.await(500);
         assertNull(found);
@@ -71,7 +71,7 @@ public class TapGestureFinderTest extends GestureFinderTest<TapGestureFinder> {
     @Test
     public void testLongTap() {
         touchOp.listen();
-        touchOp.start();
+        touchOp.controller().start();
         GeneralClickAction a = new GeneralClickAction(
                 Tap.LONG, GeneralLocation.CENTER, Press.FINGER,
                 InputDevice.SOURCE_UNKNOWN, MotionEvent.BUTTON_PRIMARY);

cameraview/src/androidTest/java/com/otaliastudios/cameraview/internal/GridLinesLayoutTest.java

@@ -4,7 +4,9 @@ package com.otaliastudios.cameraview.internal;
 import com.otaliastudios.cameraview.BaseTest;
 import com.otaliastudios.cameraview.TestActivity;
 import com.otaliastudios.cameraview.controls.Grid;
+import com.otaliastudios.cameraview.tools.Op;
 
+import androidx.annotation.NonNull;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import androidx.test.filters.MediumTest;
 import androidx.test.rule.ActivityTestRule;
@@ -15,6 +17,7 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
 
 @RunWith(AndroidJUnit4.class)
 @MediumTest
@@ -25,6 +28,14 @@ public class GridLinesLayoutTest extends BaseTest {
 
     private GridLinesLayout layout;
 
+    @NonNull
+    private Op<Integer> getDrawOp() {
+        final Op<Integer> op = new Op<>();
+        layout.callback = mock(GridLinesLayout.DrawCallback.class);
+        doEndOp(op, 0).when(layout.callback).onDraw(anyInt());
+        return op;
+    }
+
     @Before
     public void setUp() {
         uiSync(new Runnable() {
@@ -33,18 +44,17 @@ public class GridLinesLayoutTest extends BaseTest {
                 TestActivity a = rule.getActivity();
                 layout = new GridLinesLayout(a);
                 layout.setGridMode(Grid.OFF);
-                layout.drawOp.listen();
+                Op<Integer> op = getDrawOp();
                 a.getContentView().addView(layout);
+                op.await(1000);
             }
         });
-        // Wait for first draw.
-        layout.drawOp.await(1000);
     }
 
     private int setGridAndWait(Grid value) {
-        layout.drawOp.listen();
         layout.setGridMode(value);
-        Integer result = layout.drawOp.await(1000);
+        Op<Integer> op = getDrawOp();
+        Integer result = op.await(1000);
         assertNotNull(result);
         return result;
     }
@@ -52,25 +62,25 @@ public class GridLinesLayoutTest extends BaseTest {
     @Test
     public void testOff() {
         int linesDrawn = setGridAndWait(Grid.OFF);
-        assertEquals(linesDrawn, 0);
+        assertEquals(0, linesDrawn);
     }
 
     @Test
     public void test3x3() {
         int linesDrawn = setGridAndWait(Grid.DRAW_3X3);
-        assertEquals(linesDrawn, 2);
+        assertEquals(2, linesDrawn);
     }
 
     @Test
     public void testPhi() {
         int linesDrawn = setGridAndWait(Grid.DRAW_PHI);
-        assertEquals(linesDrawn, 2);
+        assertEquals(2, linesDrawn);
     }
 
     @Test
     public void test4x4() {
         int linesDrawn = setGridAndWait(Grid.DRAW_4X4);
-        assertEquals(linesDrawn, 3);
+        assertEquals(3, linesDrawn);
     }
 
 }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/internal/utils/CamcorderProfilesTest.java

@@ -8,7 +8,7 @@ import androidx.test.filters.SmallTest;
 
 import com.otaliastudios.cameraview.BaseTest;
 import com.otaliastudios.cameraview.CameraUtils;
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 import com.otaliastudios.cameraview.size.Size;
 
 import org.junit.Test;

cameraview/src/androidTest/java/com/otaliastudios/cameraview/internal/utils/ImageHelperTest.java

@@ -18,11 +18,11 @@ import android.view.Surface;
 
 import androidx.annotation.NonNull;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
-import androidx.test.filters.SdkSuppress;
 import androidx.test.filters.SmallTest;
 
 import com.otaliastudios.cameraview.BaseTest;
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.Op;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -45,12 +45,12 @@ public class ImageHelperTest extends BaseTest {
     private Image getImage() {
         ImageReader reader = ImageReader.newInstance(100, 100, ImageFormat.YUV_420_888, 1);
         Surface readerSurface = reader.getSurface();
-        final Op<Image> imageOp = new Op<>(true);
+        final Op<Image> imageOp = new Op<>();
         reader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() {
             @Override
             public void onImageAvailable(ImageReader reader) {
                 Image image = reader.acquireLatestImage();
-                if (image != null) imageOp.end(image);
+                if (image != null) imageOp.controller().end(image);
             }
         }, new Handler(Looper.getMainLooper()));
 

cameraview/src/androidTest/java/com/otaliastudios/cameraview/internal/utils/WorkerHandlerTest.java

@@ -4,6 +4,7 @@ package com.otaliastudios.cameraview.internal.utils;
 import com.google.android.gms.tasks.Task;
 import com.google.android.gms.tasks.Tasks;
 import com.otaliastudios.cameraview.BaseTest;
+import com.otaliastudios.cameraview.tools.Op;
 
 import androidx.annotation.NonNull;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
@@ -13,7 +14,6 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import java.util.concurrent.Callable;
-import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 
@@ -43,7 +43,7 @@ public class WorkerHandlerTest extends BaseTest {
         return new Runnable() {
             @Override
             public void run() {
-                op.end(true);
+                op.controller().end(true);
             }
         };
     }
@@ -53,7 +53,7 @@ public class WorkerHandlerTest extends BaseTest {
         return new Callable<Boolean>() {
             @Override
             public Boolean call() {
-                op.end(true);
+                op.controller().end(true);
                 return true;
             }
         };
@@ -77,7 +77,7 @@ public class WorkerHandlerTest extends BaseTest {
 
     @Test
     public void testFallbackExecute() {
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         WorkerHandler.execute(getRunnableForOp(op));
         waitOp(op);
     }
@@ -85,7 +85,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testPostRunnable() {
         WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.post(getRunnableForOp(op));
         waitOp(op);
     }
@@ -93,7 +93,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testPostCallable() {
         WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.post(getCallableForOp(op));
         waitOp(op);
     }
@@ -110,7 +110,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRunRunnable_background() {
         WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.run(getRunnableForOp(op));
         waitOp(op);
     }
@@ -118,14 +118,14 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRunRunnable_sameThread() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op1 = new Op<>(true);
+        final Op<Boolean> op1 = new Op<>();
-        final Op<Boolean> op2 = new Op<>(true);
+        final Op<Boolean> op2 = new Op<>();
         handler.post(new Runnable() {
             @Override
             public void run() {
                 handler.run(getRunnableForOp(op2));
                 assertTrue(op2.await(0)); // Do not wait.
-                op1.end(true);
+                op1.controller().end(true);
             }
         });
         waitOp(op1);
@@ -134,7 +134,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRunCallable_background() {
         WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.run(getCallableForOp(op));
         waitOp(op);
     }
@@ -142,14 +142,14 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRunCallable_sameThread() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op1 = new Op<>(true);
+        final Op<Boolean> op1 = new Op<>();
-        final Op<Boolean> op2 = new Op<>(true);
+        final Op<Boolean> op2 = new Op<>();
         handler.post(new Runnable() {
             @Override
             public void run() {
                 handler.run(getCallableForOp(op2));
                 assertTrue(op2.await(0)); // Do not wait.
-                op1.end(true);
+                op1.controller().end(true);
             }
         });
         waitOp(op1);
@@ -158,14 +158,14 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRunCallable_sameThread_throws() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.post(new Runnable() {
             @Override
             public void run() {
                 Task<Void> task = handler.run(getThrowCallable());
                 assertTrue(task.isComplete()); // Already complete
                 assertFalse(task.isSuccessful());
-                op.end(true);
+                op.controller().end(true);
             }
         });
         waitOp(op);
@@ -174,7 +174,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testPostDelayed_tooEarly() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.post(1000, getRunnableForOp(op));
         assertNull(op.await(500));
     }
@@ -182,7 +182,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testPostDelayed() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         handler.post(1000, getRunnableForOp(op));
         assertNotNull(op.await(2000));
     }
@@ -190,7 +190,7 @@ public class WorkerHandlerTest extends BaseTest {
     @Test
     public void testRemove() {
         final WorkerHandler handler = WorkerHandler.get("handler");
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         Runnable runnable = getRunnableForOp(op);
         handler.post(1000, runnable);
         handler.remove(runnable);
@@ -210,7 +210,7 @@ public class WorkerHandlerTest extends BaseTest {
     public void testExecutor() {
         final WorkerHandler handler = WorkerHandler.get("handler");
         Executor executor = handler.getExecutor();
-        final Op<Boolean> op = new Op<>(true);
+        final Op<Boolean> op = new Op<>();
         executor.execute(getRunnableForOp(op));
         waitOp(op);
     }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/markers/MarkerLayoutTest.java

@@ -9,7 +9,7 @@ import android.view.ViewGroup;
 
 import com.otaliastudios.cameraview.BaseTest;
 import com.otaliastudios.cameraview.TestActivity;
-import com.otaliastudios.cameraview.runner.SdkExclude;
+import com.otaliastudios.cameraview.tools.SdkExclude;
 
 import org.junit.Assert;
 import org.junit.Before;

cameraview/src/androidTest/java/com/otaliastudios/cameraview/preview/CameraPreviewTest.java

@@ -7,7 +7,7 @@ import android.view.ViewGroup;
 
 import com.otaliastudios.cameraview.BaseTest;
 import com.otaliastudios.cameraview.TestActivity;
-import com.otaliastudios.cameraview.internal.utils.Op;
+import com.otaliastudios.cameraview.tools.Op;
 import com.otaliastudios.cameraview.size.AspectRatio;
 import com.otaliastudios.cameraview.size.Size;
 
@@ -42,8 +42,8 @@ public abstract class CameraPreviewTest<T extends CameraPreview> extends BaseTes
 
     @Before
     public void setUp() {
-        available = new Op<>(true);
+        available = new Op<>();
-        destroyed = new Op<>(true);
+        destroyed = new Op<>();
 
         uiSync(new Runnable() {
             @Override
@@ -55,7 +55,7 @@ public abstract class CameraPreviewTest<T extends CameraPreview> extends BaseTes
                 doAnswer(new Answer() {
                     @Override
                     public Object answer(InvocationOnMock invocation) {
-                        if (available != null) available.end(true);
+                        if (available != null) available.controller().end(true);
                         return null;
                     }
                 }).when(callback).onSurfaceAvailable();
@@ -63,7 +63,7 @@ public abstract class CameraPreviewTest<T extends CameraPreview> extends BaseTes
                 doAnswer(new Answer() {
                     @Override
                     public Object answer(InvocationOnMock invocation) {
-                        if (destroyed != null) destroyed.end(true);
+                        if (destroyed != null) destroyed.controller().end(true);
                         return null;
                     }
                 }).when(callback).onSurfaceDestroyed();
@@ -153,17 +153,23 @@ public abstract class CameraPreviewTest<T extends CameraPreview> extends BaseTes
 
         // Since desired is 'desired', let's fake a new view size that is consistent with it.
         // Ensure crop is not happening anymore.
-        preview.mCropOp.listen();
+        preview.mCropCallback = mock(CameraPreview.CropCallback.class);
-        preview.dispatchOnSurfaceSizeChanged((int) (50f * desired), 50); // Wait...
+        Op<Void> op = new Op<>();
-        preview.mCropOp.await();
+        doEndOp(op, null).when(preview.mCropCallback).onCrop();
+        preview.dispatchOnSurfaceSizeChanged((int) (50f * desired), 50);
+
+        op.await(); // Wait...
         assertEquals(desired, getViewAspectRatioWithScale(), 0.01f);
         assertFalse(preview.isCropping());
     }
 
     private void setDesiredAspectRatio(float desiredAspectRatio) {
-        preview.mCropOp.listen();
+        preview.mCropCallback = mock(CameraPreview.CropCallback.class);
-        preview.setStreamSize((int) (10f * desiredAspectRatio), 10); // Wait...
+        Op<Void> op = new Op<>();
-        preview.mCropOp.await();
+        doEndOp(op, null).when(preview.mCropCallback).onCrop();
+        preview.setStreamSize((int) (10f * desiredAspectRatio), 10);
+
+        op.await(); // Wait...
         assertEquals(desiredAspectRatio, getViewAspectRatioWithScale(), 0.01f);
 
     }

cameraview/src/androidTest/java/com/otaliastudios/cameraview/tools/Op.java

@@ -0,0 +1,149 @@
+package com.otaliastudios.cameraview.tools;
+
+import androidx.annotation.NonNull;
+
+import com.google.android.gms.tasks.OnSuccessListener;
+import com.google.android.gms.tasks.Task;
+import com.otaliastudios.cameraview.controls.Control;
+
+import org.mockito.Mockito;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
+import org.mockito.stubbing.Stubber;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A naive implementation of {@link java.util.concurrent.CountDownLatch}
+ * to help in testing.
+ */
+public class Op<T> {
+
+    public class Controller {
+        private int mToBeIgnored;
+
+        private Controller() { }
+
+        /** Op owner method: notifies the action started. */
+        public void start() {
+            if (!isListening()) mToBeIgnored++;
+        }
+
+        /** Op owner method: notifies the action ended. */
+        public void end(T result) {
+            if (mToBeIgnored > 0) {
+                mToBeIgnored--;
+                return;
+            }
+
+            if (isListening()) { // Should be always true.
+                mResult = result;
+                mLatch.countDown();
+            }
+        }
+
+        public void from(@NonNull Task<T> task) {
+            start();
+            task.addOnSuccessListener(new OnSuccessListener<T>() {
+                @Override
+                public void onSuccess(T result) {
+                    end(result);
+                }
+            });
+        }
+
+        @NonNull
+        public Stubber from(final int invocationArgument) {
+            return Mockito.doAnswer(new Answer() {
+                @Override
+                public Object answer(InvocationOnMock invocation) {
+                    //noinspection unchecked
+                    T o = (T) invocation.getArguments()[invocationArgument];
+                    start();
+                    end(o);
+                    return null;
+                }
+            });
+        }
+    }
+
+    private CountDownLatch mLatch;
+    private Controller mController = new Controller();
+    private T mResult;
+
+    /**
+     * Listeners should:
+     * - call {@link #listen()} to notify they are interested in the next action
+     * - call {@link #await()} to know when the action is performed.
+     *
+     * Op owners should:
+     * - call {@link Controller#start()} when task started
+     * - call {@link Controller#end(Object)} when task ends
+     */
+    public Op() {
+        this(true);
+    }
+
+    public Op(boolean startListening) {
+        if (startListening) listen();
+    }
+
+    public Op(@NonNull Task<T> task) {
+        listen();
+        controller().from(task);
+    }
+
+    private boolean isListening() {
+        return mLatch != null;
+    }
+
+    /**
+     * Listener method: notifies we are interested in the next action.
+     */
+    public void listen() {
+        if (isListening()) throw new RuntimeException("Should not happen.");
+        mResult = null;
+        mLatch = new CountDownLatch(1);
+    }
+
+    /**
+     * Listener method: waits for next task action to end.
+     * @param millis milliseconds
+     * @return the action result
+     */
+    public T await(long millis) {
+        return await(millis, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Listener method: waits 1 minute for next task action to end.
+     * @return the action result
+     */
+    public T await() {
+        return await(1, TimeUnit.MINUTES);
+    }
+
+    /**
+     * Listener method: waits for next task action to end.
+     * @param time time
+     * @param unit the time unit
+     * @return the action result
+     */
+    private T await(long time, @NonNull TimeUnit unit) {
+        try {
+            mLatch.await(time, unit);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+        T result = mResult;
+        mResult = null;
+        mLatch = null;
+        return result;
+    }
+
+    @NonNull
+    public Controller controller() {
+        return mController;
+    }
+}

cameraview/src/androidTest/java/com/otaliastudios/cameraview/tools/SdkExclude.java

@@ -1,4 +1,4 @@
-package com.otaliastudios.cameraview.runner;
+package com.otaliastudios.cameraview.tools;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;

cameraview/src/androidTest/java/com/otaliastudios/cameraview/tools/SdkExcludeFilter.java

@@ -1,4 +1,4 @@
-package com.otaliastudios.cameraview.runner;
+package com.otaliastudios.cameraview.tools;
 
 
 import android.os.Build;

cameraview/src/main/java/com/otaliastudios/cameraview/CameraView.java

@@ -48,6 +48,7 @@ import com.otaliastudios.cameraview.engine.Camera1Engine;
 import com.otaliastudios.cameraview.engine.Camera2Engine;
 import com.otaliastudios.cameraview.engine.CameraEngine;
 import com.otaliastudios.cameraview.engine.offset.Reference;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.filter.Filter;
 import com.otaliastudios.cameraview.filter.FilterParser;
 import com.otaliastudios.cameraview.filter.Filters;
@@ -693,15 +694,17 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
     //region Lifecycle APIs
 
     /**
-     * Returns whether the camera has started showing its preview.
+     * Returns whether the camera engine has started.
      * @return whether the camera has started
      */
     public boolean isOpened() {
-        return mCameraEngine.getEngineState() >= CameraEngine.STATE_STARTED;
+        return mCameraEngine.getState().isAtLeast(CameraState.ENGINE)
+                && mCameraEngine.getTargetState().isAtLeast(CameraState.ENGINE);
     }
 
     private boolean isClosed() {
-        return mCameraEngine.getEngineState() == CameraEngine.STATE_STOPPED;
+        return mCameraEngine.getState() == CameraState.OFF
+                && !mCameraEngine.isChangingState();
     }
 
     /**
@@ -792,7 +795,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
     @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
     public void close() {
         if (mInEditor) return;
-        mCameraEngine.stop();
+        mCameraEngine.stop(false);
         if (mCameraPreview != null) mCameraPreview.onPause();
     }
 
@@ -2006,7 +2009,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
 
         @Override
-        public void dispatchOnCameraOpened(final CameraOptions options) {
+        public void dispatchOnCameraOpened(@NonNull final CameraOptions options) {
             mLogger.i("dispatchOnCameraOpened", options);
             mUiHandler.post(new Runnable() {
                 @Override
@@ -2054,7 +2057,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
 
         @Override
-        public void dispatchOnPictureTaken(final PictureResult.Stub stub) {
+        public void dispatchOnPictureTaken(@NonNull final PictureResult.Stub stub) {
             mLogger.i("dispatchOnPictureTaken", stub);
             mUiHandler.post(new Runnable() {
                 @Override
@@ -2068,7 +2071,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         }
 
         @Override
-        public void dispatchOnVideoTaken(final VideoResult.Stub stub) {
+        public void dispatchOnVideoTaken(@NonNull final VideoResult.Stub stub) {
             mLogger.i("dispatchOnVideoTaken", stub);
             mUiHandler.post(new Runnable() {
                 @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera1Engine.java

@@ -24,6 +24,7 @@ import com.otaliastudios.cameraview.engine.mappers.Camera1Mapper;
 import com.otaliastudios.cameraview.engine.offset.Axis;
 import com.otaliastudios.cameraview.engine.offset.Reference;
 import com.otaliastudios.cameraview.engine.options.Camera1Options;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.PictureResult;
 import com.otaliastudios.cameraview.VideoResult;
@@ -49,7 +50,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 
-@SuppressWarnings("deprecation")
 public class Camera1Engine extends CameraEngine implements
         Camera.PreviewCallback,
         Camera.ErrorCallback,
@@ -58,13 +58,15 @@ public class Camera1Engine extends CameraEngine implements
     private static final String TAG = Camera1Engine.class.getSimpleName();
     private static final CameraLogger LOG = CameraLogger.create(TAG);
 
+    private static final String JOB_FOCUS_RESET = "focus reset";
+    private static final String JOB_FOCUS_END = "focus end";
+
     private static final int PREVIEW_FORMAT = ImageFormat.NV21;
     @VisibleForTesting static final int AUTOFOCUS_END_DELAY_MILLIS = 2500;
 
     private final Camera1Mapper mMapper = Camera1Mapper.get();
     private Camera mCamera;
     @VisibleForTesting int mCameraId;
-    private Runnable mFocusEndRunnable;
 
     public Camera1Engine(@NonNull Callback callback) {
         super(callback);
@@ -286,10 +288,8 @@ public class Camera1Engine extends CameraEngine implements
     @Override
     protected Task<Void> onStopEngine() {
         LOG.i("onStopEngine:", "About to clean up.");
-        mHandler.remove(mFocusResetRunnable);
+        mOrchestrator.remove(JOB_FOCUS_RESET);
-        if (mFocusEndRunnable != null) {
+        mOrchestrator.remove(JOB_FOCUS_END);
-            mHandler.remove(mFocusEndRunnable);
-        }
         if (mCamera != null) {
             try {
                 LOG.i("onStopEngine:", "Clean up.", "Releasing camera.");
@@ -457,15 +457,14 @@ public class Camera1Engine extends CameraEngine implements
     public void setFlash(@NonNull Flash flash) {
         final Flash old = mFlash;
         mFlash = flash;
-        mHandler.run(new Runnable() {
+        mFlashTask = mOrchestrator.scheduleStateful("flash",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyFlash(params, old)) mCamera.setParameters(params);
             }
-                mFlashOp.end(null);
-            }
         });
     }
 
@@ -482,15 +481,14 @@ public class Camera1Engine extends CameraEngine implements
     public void setLocation(@Nullable Location location) {
         final Location oldLocation = mLocation;
         mLocation = location;
-        mHandler.run(new Runnable() {
+        mLocationTask = mOrchestrator.scheduleStateful("location",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyLocation(params, oldLocation)) mCamera.setParameters(params);
             }
-                mLocationOp.end(null);
-            }
         });
     }
 
@@ -510,15 +508,14 @@ public class Camera1Engine extends CameraEngine implements
     public void setWhiteBalance(@NonNull WhiteBalance whiteBalance) {
         final WhiteBalance old = mWhiteBalance;
         mWhiteBalance = whiteBalance;
-        mHandler.run(new Runnable() {
+        mWhiteBalanceTask = mOrchestrator.scheduleStateful("white balance",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyWhiteBalance(params, old)) mCamera.setParameters(params);
             }
-                mWhiteBalanceOp.end(null);
-            }
         });
     }
 
@@ -536,15 +533,14 @@ public class Camera1Engine extends CameraEngine implements
     public void setHdr(@NonNull Hdr hdr) {
         final Hdr old = mHdr;
         mHdr = hdr;
-        mHandler.run(new Runnable() {
+        mHdrTask = mOrchestrator.scheduleStateful("hdr",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyHdr(params, old)) mCamera.setParameters(params);
             }
-                mHdrOp.end(null);
-            }
         });
     }
 
@@ -561,10 +557,11 @@ public class Camera1Engine extends CameraEngine implements
     public void setZoom(final float zoom, @Nullable final PointF[] points, final boolean notify) {
         final float old = mZoomValue;
         mZoomValue = zoom;
-        mHandler.run(new Runnable() {
+        mZoomTask = mOrchestrator.scheduleStateful("zoom",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyZoom(params, old)) {
                     mCamera.setParameters(params);
@@ -573,8 +570,6 @@ public class Camera1Engine extends CameraEngine implements
                     }
                 }
             }
-                mZoomOp.end(null);
-            }
         });
     }
 
@@ -594,10 +589,11 @@ public class Camera1Engine extends CameraEngine implements
                                       @Nullable final PointF[] points, final boolean notify) {
         final float old = mExposureCorrectionValue;
         mExposureCorrectionValue = EVvalue;
-        mHandler.run(new Runnable() {
+        mExposureCorrectionTask = mOrchestrator.scheduleStateful("exposure correction",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyExposureCorrection(params, old)) {
                     mCamera.setParameters(params);
@@ -607,8 +603,6 @@ public class Camera1Engine extends CameraEngine implements
                     }
                 }
             }
-                mExposureCorrectionOp.end(null);
-            }
         });
     }
 
@@ -635,14 +629,13 @@ public class Camera1Engine extends CameraEngine implements
     public void setPlaySounds(boolean playSounds) {
         final boolean old = mPlaySounds;
         mPlaySounds = playSounds;
-        mHandler.run(new Runnable() {
+        mPlaySoundsTask = mOrchestrator.scheduleStateful("play sounds",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 applyPlaySounds(old);
             }
-                mPlaySoundsOp.end(null);
-            }
         });
     }
 
@@ -672,15 +665,14 @@ public class Camera1Engine extends CameraEngine implements
     public void setPreviewFrameRate(float previewFrameRate) {
         final float old = previewFrameRate;
         mPreviewFrameRate = previewFrameRate;
-        mHandler.run(new Runnable() {
+        mPreviewFrameRateTask = mOrchestrator.scheduleStateful("preview fps",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 Camera.Parameters params = mCamera.getParameters();
                 if (applyPreviewFrameRate(params, old)) mCamera.setParameters(params);
             }
-                mPreviewFrameRateOp.end(null);
-            }
         });
     }
 
@@ -737,7 +729,8 @@ public class Camera1Engine extends CameraEngine implements
 
     @Override
     public void onBufferAvailable(@NonNull byte[] buffer) {
-        if (getEngineState() == STATE_STARTED) {
+        if (getState().isAtLeast(CameraState.ENGINE)
+                && getTargetState().isAtLeast(CameraState.ENGINE)) {
             mCamera.addCallbackBuffer(buffer);
         }
     }
@@ -770,10 +763,9 @@ public class Camera1Engine extends CameraEngine implements
         }
         final int viewWidthF = viewWidth;
         final int viewHeightF = viewHeight;
-        mHandler.run(new Runnable() {
+        mOrchestrator.scheduleStateful("auto focus", CameraState.ENGINE, new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() < STATE_STARTED) return;
                 if (!mCameraOptions.isAutoFocusSupported()) return;
                 final PointF p = new PointF(point.x, point.y); // copy.
                 int offset = getAngles().offset(Reference.SENSOR, Reference.VIEW, Axis.ABSOLUTE);
@@ -794,14 +786,14 @@ public class Camera1Engine extends CameraEngine implements
 
                 // The auto focus callback is not guaranteed to be called, but we really want it
                 // to be. So we remove the old runnable if still present and post a new one.
-                if (mFocusEndRunnable != null) mHandler.remove(mFocusEndRunnable);
+                mOrchestrator.remove(JOB_FOCUS_END);
-                mFocusEndRunnable = new Runnable() {
+                mOrchestrator.scheduleDelayed(JOB_FOCUS_END, AUTOFOCUS_END_DELAY_MILLIS,
+                        new Runnable() {
                     @Override
                     public void run() {
                         mCallback.dispatchOnFocusEnd(gesture, false, p);
                     }
-                };
+                });
-                mHandler.post(AUTOFOCUS_END_DELAY_MILLIS, mFocusEndRunnable);
 
                 // Wrapping autoFocus in a try catch to handle some device specific exceptions,
                 // see See https://github.com/natario1/CameraView/issues/181.
@@ -809,14 +801,27 @@ public class Camera1Engine extends CameraEngine implements
                     mCamera.autoFocus(new Camera.AutoFocusCallback() {
                         @Override
                         public void onAutoFocus(boolean success, Camera camera) {
-                            if (mFocusEndRunnable != null) {
+                            mOrchestrator.remove(JOB_FOCUS_END);
-                                mHandler.remove(mFocusEndRunnable);
+                            mOrchestrator.remove(JOB_FOCUS_RESET);
-                                mFocusEndRunnable = null;
-                            }
                             mCallback.dispatchOnFocusEnd(gesture, success, p);
-                            mHandler.remove(mFocusResetRunnable);
                             if (shouldResetAutoFocus()) {
-                                mHandler.post(getAutoFocusResetDelay(), mFocusResetRunnable);
+                                mOrchestrator.scheduleStatefulDelayed(
+                                        JOB_FOCUS_RESET,
+                                        CameraState.ENGINE,
+                                        getAutoFocusResetDelay(),
+                                        new Runnable() {
+                                    @Override
+                                    public void run() {
+                                        mCamera.cancelAutoFocus();
+                                        Camera.Parameters params = mCamera.getParameters();
+                                        int maxAF = params.getMaxNumFocusAreas();
+                                        int maxAE = params.getMaxNumMeteringAreas();
+                                        if (maxAF > 0) params.setFocusAreas(null);
+                                        if (maxAE > 0) params.setMeteringAreas(null);
+                                        applyDefaultFocus(params); // Revert to internal focus.
+                                        mCamera.setParameters(params);
+                                    }
+                                });
                             }
                         }
                     });
@@ -825,7 +830,6 @@ public class Camera1Engine extends CameraEngine implements
                     // Let the mFocusEndRunnable do its job. (could remove it and quickly dispatch
                     // onFocusEnd here, but let's make it simpler).
                 }
-
             }
         });
     }
@@ -876,21 +880,6 @@ public class Camera1Engine extends CameraEngine implements
         return new Rect(left, top, right, bottom);
     }
 
-    private final Runnable mFocusResetRunnable = new Runnable() {
-        @Override
-        public void run() {
-            if (getEngineState() < STATE_STARTED) return;
-            mCamera.cancelAutoFocus();
-            Camera.Parameters params = mCamera.getParameters();
-            int maxAF = params.getMaxNumFocusAreas();
-            int maxAE = params.getMaxNumMeteringAreas();
-            if (maxAF > 0) params.setFocusAreas(null);
-            if (maxAE > 0) params.setMeteringAreas(null);
-            applyDefaultFocus(params); // Revert to internal focus.
-            mCamera.setParameters(params);
-        }
-    };
-
     //endregion
 }
 

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Camera2Engine.java

@@ -48,12 +48,14 @@ import com.otaliastudios.cameraview.engine.action.ActionHolder;
 import com.otaliastudios.cameraview.engine.action.Actions;
 import com.otaliastudios.cameraview.engine.action.BaseAction;
 import com.otaliastudios.cameraview.engine.action.CompletionCallback;
+import com.otaliastudios.cameraview.engine.action.LogAction;
 import com.otaliastudios.cameraview.engine.mappers.Camera2Mapper;
 import com.otaliastudios.cameraview.engine.meter.MeterAction;
 import com.otaliastudios.cameraview.engine.meter.MeterResetAction;
 import com.otaliastudios.cameraview.engine.offset.Axis;
 import com.otaliastudios.cameraview.engine.offset.Reference;
 import com.otaliastudios.cameraview.engine.options.Camera2Options;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameManager;
 import com.otaliastudios.cameraview.gesture.Gesture;
@@ -243,7 +245,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     }
 
     private void applyRepeatingRequestBuilder(boolean checkStarted, int errorReason) {
-        if (getPreviewState() == STATE_STARTED || !checkStarted) {
+        if ((getState() == CameraState.PREVIEW && !isChangingState()) || !checkStarted) {
             try {
                 mSession.setRepeatingRequest(mRepeatingRequestBuilder.build(),
                         mRepeatingRequestCallback, null);
@@ -256,9 +258,8 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                 LOG.e("applyRepeatingRequestBuilder: session is invalid!", e,
                         "checkStarted:", checkStarted,
                         "currentThread:", Thread.currentThread().getName(),
-                        "previewState:", getPreviewState(),
+                        "state:", getState(),
-                        "bindState:", getBindState(),
+                        "targetState:", getTargetState());
-                        "engineState:", getEngineState());
                 throw new CameraException(CameraException.REASON_DISCONNECTED);
             }
         }
@@ -588,13 +589,12 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         if (mFullVideoPendingStub != null) {
             // Do not call takeVideo/onTakeVideo. It will reset some stub parameters that
             // the recorder sets. Also we are posting so that doTakeVideo sees a started preview.
-            LOG.i("onStartPreview", "Posting doTakeVideo call.");
             final VideoResult.Stub stub = mFullVideoPendingStub;
             mFullVideoPendingStub = null;
-            mHandler.post(new Runnable() {
+            mOrchestrator.scheduleStateful("do take video", CameraState.PREVIEW,
+                    new Runnable() {
                 @Override
                 public void run() {
-                    LOG.i("onStartPreview", "Executing doTakeVideo call.");
                     doTakeVideo(stub);
                 }
             });
@@ -895,10 +895,10 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         // SnapshotRecorder will invoke this on its own thread, so let's post in our own thread
         // and check camera state before trying to restore the preview. Engine might have been
         // torn down in the engine thread while this was still being called.
-        mHandler.run(new Runnable() {
+        mOrchestrator.scheduleStateful("restore preview template", CameraState.BIND,
+                new Runnable() {
             @Override
             public void run() {
-                if (getBindState() < STATE_STARTED) return;
                 maybeRestorePreviewTemplateAfterVideo();
             }
         });
@@ -1028,12 +1028,13 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setFlash(@NonNull final Flash flash) {
         final Flash old = mFlash;
         mFlash = flash;
-        mHandler.run(new Runnable() {
+        mFlashTask = mOrchestrator.scheduleStateful("flash (" + flash + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 boolean shouldApply = applyFlash(mRepeatingRequestBuilder, old);
-                    boolean needsWorkaround = getPreviewState() == STATE_STARTED;
+                boolean needsWorkaround = getState() == CameraState.PREVIEW;
                 if (needsWorkaround) {
                     // Runtime changes to the flash value are not correctly handled by the
                     // driver. See https://stackoverflow.com/q/53003383/4288782 for example.
@@ -1054,8 +1055,6 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     applyRepeatingRequestBuilder();
                 }
             }
-                mFlashOp.end(null);
-            }
         });
     }
 
@@ -1104,16 +1103,15 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setLocation(@Nullable Location location) {
         final Location old = mLocation;
         mLocation = location;
-        mHandler.run(new Runnable() {
+        mLocationTask = mOrchestrator.scheduleStateful("location",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyLocation(mRepeatingRequestBuilder, old)) {
                     applyRepeatingRequestBuilder();
                 }
             }
-                mLocationOp.end(null);
-            }
         });
     }
 
@@ -1130,16 +1128,16 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setWhiteBalance(@NonNull WhiteBalance whiteBalance) {
         final WhiteBalance old = mWhiteBalance;
         mWhiteBalance = whiteBalance;
-        mHandler.run(new Runnable() {
+        mWhiteBalanceTask = mOrchestrator.scheduleStateful(
+                "white balance (" + whiteBalance + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyWhiteBalance(mRepeatingRequestBuilder, old)) {
                     applyRepeatingRequestBuilder();
                 }
             }
-                mWhiteBalanceOp.end(null);
-            }
         });
     }
 
@@ -1159,16 +1157,15 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setHdr(@NonNull Hdr hdr) {
         final Hdr old = mHdr;
         mHdr = hdr;
-        mHandler.run(new Runnable() {
+        mHdrTask = mOrchestrator.scheduleStateful("hdr (" + hdr + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyHdr(mRepeatingRequestBuilder, old)) {
                     applyRepeatingRequestBuilder();
                 }
             }
-                mHdrOp.end(null);
-            }
         });
     }
 
@@ -1187,10 +1184,12 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setZoom(final float zoom, final @Nullable PointF[] points, final boolean notify) {
         final float old = mZoomValue;
         mZoomValue = zoom;
-        mHandler.run(new Runnable() {
+        mZoomTask = mOrchestrator.scheduleStateful(
+                "zoom (" + zoom + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyZoom(mRepeatingRequestBuilder, old)) {
                     applyRepeatingRequestBuilder();
                     if (notify) {
@@ -1198,8 +1197,6 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     }
                 }
             }
-                mZoomOp.end(null);
-            }
         });
     }
 
@@ -1243,10 +1240,12 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                                       final boolean notify) {
         final float old = mExposureCorrectionValue;
         mExposureCorrectionValue = EVvalue;
-        mHandler.run(new Runnable() {
+        mExposureCorrectionTask = mOrchestrator.scheduleStateful(
+                "exposure correction (" + EVvalue + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyExposureCorrection(mRepeatingRequestBuilder, old)) {
                     applyRepeatingRequestBuilder();
                     if (notify) {
@@ -1254,8 +1253,6 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     }
                 }
             }
-                mExposureCorrectionOp.end(null);
-            }
         });
     }
 
@@ -1278,22 +1275,23 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     @Override
     public void setPlaySounds(boolean playSounds) {
         mPlaySounds = playSounds;
-        mPlaySoundsOp.end(null);
+        mPlaySoundsTask = Tasks.forResult(null);
     }
 
-    @Override public void setPreviewFrameRate(float previewFrameRate) {
+    @Override
+    public void setPreviewFrameRate(float previewFrameRate) {
         final float oldPreviewFrameRate = mPreviewFrameRate;
         mPreviewFrameRate = previewFrameRate;
-        mHandler.run(new Runnable() {
+        mPreviewFrameRateTask = mOrchestrator.scheduleStateful(
+                "preview fps (" + previewFrameRate + ")",
+                CameraState.ENGINE,
+                new Runnable() {
             @Override
             public void run() {
-                if (getEngineState() == STATE_STARTED) {
                 if (applyPreviewFrameRate(mRepeatingRequestBuilder, oldPreviewFrameRate)) {
                     applyRepeatingRequestBuilder();
                 }
             }
-                mPreviewFrameRateOp.end(null);
-            }
         });
     }
 
@@ -1334,20 +1332,13 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     public void setPictureFormat(final @NonNull PictureFormat pictureFormat) {
         if (pictureFormat != mPictureFormat) {
             mPictureFormat = pictureFormat;
-            LOG.i("setPictureFormat", "changing to", pictureFormat, "posting.");
+            mOrchestrator.scheduleStateful("picture format (" + pictureFormat + ")",
-            mHandler.run(new Runnable() {
+                    CameraState.ENGINE,
+                    new Runnable() {
                 @Override
                 public void run() {
-                    LOG.i("setPictureFormat", "changing to", pictureFormat,
-                            "executing. EngineState:", getEngineState(),
-                            "BindState:", getBindState());
-                    if (getEngineState() == STATE_STOPPED) {
-                        LOG.i("setPictureFormat", "not started so won't restart.");
-                    } else {
-                        LOG.i("setPictureFormat", "started or starting. Calling restart()");
                     restart();
                 }
-                }
             });
         }
     }
@@ -1391,7 +1382,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
             return;
         }
         image.close();
-        if (getPreviewState() == STATE_STARTED) {
+        if (getState() == CameraState.PREVIEW && !isChangingState()) {
             // After preview, the frame manager is correctly set up
             Frame frame = getFrameManager().getFrame(data,
                     System.currentTimeMillis(),
@@ -1405,35 +1396,23 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     @Override
     public void setHasFrameProcessors(final boolean hasFrameProcessors) {
-        LOG.i("setHasFrameProcessors", "changing to", hasFrameProcessors, "posting.");
+        // Frame processing is set up partially when binding and partially when starting
-        Camera2Engine.super.setHasFrameProcessors(hasFrameProcessors);
+        // the preview. If the value is changed between the two, the preview step can crash.
-        mHandler.run(new Runnable() {
+        mOrchestrator.schedule("has frame processors (" + hasFrameProcessors + ")",
+                true, new Runnable() {
             @Override
             public void run() {
-                LOG.i("setHasFrameProcessors", "changing to", hasFrameProcessors,
+                if (getState().isAtLeast(CameraState.BIND) && isChangingState()) {
-                        "executing. BindState:", getBindState(),
+                    // Extremely rare case in which this was called in between startBind and
-                        "PreviewState:", getPreviewState());
+                    // startPreview. This can cause issues. Try later.
-
+                    setHasFrameProcessors(hasFrameProcessors);
-                // Frame processing is set up partially when binding and partially when starting
+                } else if (getState().isAtLeast(CameraState.BIND)) {
-                // the preview. We don't want to only check bind state or startPreview can fail.
+                    // Apply and restart.
-                if (getBindState() == STATE_STOPPED) {
+                    Camera2Engine.super.setHasFrameProcessors(hasFrameProcessors);
-                    LOG.i("setHasFrameProcessors", "not bound so won't restart.");
-                } else if (getPreviewState() == STATE_STARTED) {
-                    // This needs a restartBind(). NOTE: if taking video, this stops it.
-                    LOG.i("setHasFrameProcessors", "bound with preview.",
-                            "Calling restartBind().");
                     restartBind();
                 } else {
-                    // Bind+Preview is not completely started yet not completely stopped.
+                    // Just apply.
-                    // This can happen if the user adds a frame processor in onCameraOpened().
+                    Camera2Engine.super.setHasFrameProcessors(hasFrameProcessors);
-                    // Supporting this would add lot of complexity to this class, and
-                    // this should be discouraged anyway since changing the frame processor number
-                    // at this time requires restarting the camera when it was just opened.
-                    // For these reasons, let's throw.
-                    throw new IllegalStateException("Added/removed a FrameProcessor at illegal " +
-                            "time. These operations should be done before opening the camera, or " +
-                            "before closing it - NOT when it just opened, for example during the " +
-                            "onCameraOpened() callback.");
                 }
             }
         });
@@ -1445,16 +1424,14 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     @Override
     public void startAutoFocus(@Nullable final Gesture gesture, @NonNull final PointF point) {
-        LOG.i("startAutoFocus", "dispatching. Gesture:", gesture);
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                LOG.i("startAutoFocus", "executing. Preview state:", getPreviewState());
         // This will only work when we have a preview, since it launches the preview
         // in the end. Even without this it would need the bind state at least,
         // since we need the preview size.
-                if (getPreviewState() < STATE_STARTED) return;
+        mOrchestrator.scheduleStateful("autofocus (" + gesture + ")",
-
+                CameraState.PREVIEW,
+                new Runnable() {
+            @Override
+            public void run() {
                 // The camera options API still has the auto focus API but it really
                 // refers to "3A metering to a specific point". Since we have a point, check.
                 if (!mCameraOptions.isAutoFocusSupported()) return;
@@ -1468,10 +1445,16 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
                     @Override
                     protected void onActionCompleted(@NonNull Action a) {
                         mCallback.dispatchOnFocusEnd(gesture, action.isSuccessful(), point);
-                        mHandler.remove(mUnlockAndResetMeteringRunnable);
+                        mOrchestrator.remove("reset metering");
                         if (shouldResetAutoFocus()) {
-                            mHandler.post(getAutoFocusResetDelay(),
+                            mOrchestrator.scheduleDelayed("reset metering",
-                                    mUnlockAndResetMeteringRunnable);
+                                    getAutoFocusResetDelay(),
+                                    new Runnable() {
+                                @Override
+                                public void run() {
+                                    unlockAndResetMetering();
+                                }
+                            });
                         }
                     }
                 });
@@ -1495,15 +1478,8 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return mMeterAction;
     }
 
-    private final Runnable mUnlockAndResetMeteringRunnable = new Runnable() {
-        @Override
-        public void run() {
-            unlockAndResetMetering();
-        }
-    };
-
     private void unlockAndResetMetering() {
-        if (getEngineState() == STATE_STARTED) {
+        if (getState() == CameraState.PREVIEW && !isChangingState()) {
             Actions.sequence(
                     new BaseAction() {
                         @Override
@@ -1566,7 +1542,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     @Override
     public void applyBuilder(@NonNull Action source, @NonNull CaptureRequest.Builder builder)
             throws CameraAccessException {
-        if (getPreviewState() == STATE_STARTED) {
+        if (getState() == CameraState.PREVIEW && !isChangingState()) {
             mSession.capture(builder.build(), mRepeatingRequestCallback, null);
         }
     }

cameraview/src/main/java/com/otaliastudios/cameraview/engine/CameraEngine.java

@@ -8,24 +8,24 @@ import android.location.Location;
 import android.os.Handler;
 import android.os.Looper;
 
-import com.google.android.gms.tasks.Continuation;
 import com.google.android.gms.tasks.OnCompleteListener;
-import com.google.android.gms.tasks.OnFailureListener;
+import com.google.android.gms.tasks.OnSuccessListener;
-import com.google.android.gms.tasks.SuccessContinuation;
-import com.google.android.gms.tasks.TaskCompletionSource;
 import com.google.android.gms.tasks.Task;
+import com.google.android.gms.tasks.Tasks;
 import com.otaliastudios.cameraview.CameraException;
 import com.otaliastudios.cameraview.CameraLogger;
 import com.otaliastudios.cameraview.CameraOptions;
 import com.otaliastudios.cameraview.PictureResult;
 import com.otaliastudios.cameraview.controls.PictureFormat;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraOrchestrator;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraState;
+import com.otaliastudios.cameraview.engine.orchestrator.CameraStateOrchestrator;
 import com.otaliastudios.cameraview.overlay.Overlay;
 import com.otaliastudios.cameraview.VideoResult;
 import com.otaliastudios.cameraview.engine.offset.Angles;
 import com.otaliastudios.cameraview.engine.offset.Reference;
 import com.otaliastudios.cameraview.frame.Frame;
 import com.otaliastudios.cameraview.frame.FrameManager;
-import com.otaliastudios.cameraview.internal.utils.Op;
 import com.otaliastudios.cameraview.internal.utils.WorkerHandler;
 import com.otaliastudios.cameraview.picture.PictureRecorder;
 import com.otaliastudios.cameraview.preview.CameraPreview;
@@ -54,7 +54,6 @@ import java.util.Collection;
 import java.util.List;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 
 
@@ -73,13 +72,8 @@ import java.util.concurrent.TimeUnit;
  * So at the end of both step 1 and 2, the engine should check if both have
  * been performed and trigger the steps 3 and 4.
  *
- * We use an abstraction for each step called {@link Step} that manages the state of
- * each step and ensures that start and stop operations, for each step, are never called if the
- * previous one has not ended.
- *
- *
  * STATE
- * We only expose generic {@link #start()} and {@link #stop()} calls to the outside.
+ * We only expose generic {@link #start()} and {@link #stop(boolean)} calls to the outside.
  * The external users of this class are most likely interested in whether we have completed step 2
  * or not, since that tells us if we can act on the camera or not, rather than knowing about
  * steps 3 and 4.
@@ -87,18 +81,11 @@ import java.util.concurrent.TimeUnit;
  * So in the {@link CameraEngine} notation,
  * - {@link #start()}: ASYNC - starts the engine (S2). When possible, at a later time,
  *                     S3 and S4 are also performed.
- * - {@link #stop()}: ASYNC - stops everything: undoes S4, then S3, then S2.
+ * - {@link #stop(boolean)}: ASYNC - stops everything: undoes S4, then S3, then S2.
  * - {@link #restart()}: ASYNC - completes a stop then a start.
- * - {@link #destroy()}: SYNC - performs a {@link #stop()} that will go on no matter the exceptions,
+ * - {@link #destroy()}: SYNC - performs a {@link #stop(boolean)} that will go on no matter what,
  *                       without throwing. Makes the engine unusable and clears resources.
  *
- * For example, we expose the engine (S2) state through {@link #getEngineState()}. It will be:
- * - {@link #STATE_STARTING} if we're into step 2
- * - {@link #STATE_STARTED} if we've completed step 2. No clue about 3 or 4.
- * - {@link #STATE_STOPPING} if we're undoing steps 4, 3 and 2.
- * - {@link #STATE_STOPPED} if we have undone steps 4, 3 and 2 (or they never started at all).
- *
- *
  * THREADING
  * Subclasses should always execute code on the thread given by {@link #mHandler}.
  * For convenience, all the setup and tear down methods are called on this engine thread:
@@ -127,17 +114,16 @@ public abstract class CameraEngine implements
 
     public interface Callback {
         @NonNull Context getContext();
-        void dispatchOnCameraOpened(CameraOptions options);
+        void dispatchOnCameraOpened(@NonNull CameraOptions options);
         void dispatchOnCameraClosed();
         void onCameraPreviewStreamSizeChanged();
         void onShutter(boolean shouldPlaySound);
-        void dispatchOnVideoTaken(VideoResult.Stub stub);
+        void dispatchOnVideoTaken(@NonNull VideoResult.Stub stub);
-        void dispatchOnPictureTaken(PictureResult.Stub stub);
+        void dispatchOnPictureTaken(@NonNull PictureResult.Stub stub);
         void dispatchOnFocusStart(@Nullable Gesture trigger, @NonNull PointF where);
         void dispatchOnFocusEnd(@Nullable Gesture trigger, boolean success, @NonNull PointF where);
         void dispatchOnZoomChanged(final float newValue, @Nullable final PointF[] fingers);
-        void dispatchOnExposureCorrectionChanged(float newValue,
+        void dispatchOnExposureCorrectionChanged(float newValue, @NonNull float[] bounds,
-                                                 @NonNull float[] bounds,
                                                  @Nullable PointF[] fingers);
         void dispatchFrame(@NonNull Frame frame);
         void dispatchError(CameraException exception);
@@ -148,15 +134,7 @@ public abstract class CameraEngine implements
     private static final String TAG = CameraEngine.class.getSimpleName();
     private static final CameraLogger LOG = CameraLogger.create(TAG);
 
-    @SuppressWarnings({"WeakerAccess", "unused"})
-    public static final int STATE_STOPPING = Step.STATE_STOPPING;
-    public static final int STATE_STOPPED = Step.STATE_STOPPED;
-    @SuppressWarnings({"WeakerAccess", "unused"})
-    public static final int STATE_STARTING = Step.STATE_STARTING;
-    public static final int STATE_STARTED = Step.STATE_STARTED;
-
     // Need to be protected
-    @SuppressWarnings("WeakerAccess") protected WorkerHandler mHandler;
     @SuppressWarnings("WeakerAccess") protected final Callback mCallback;
     @SuppressWarnings("WeakerAccess") protected CameraPreview mPreview;
     @SuppressWarnings("WeakerAccess") protected CameraOptions mCameraOptions;
@@ -177,7 +155,7 @@ public abstract class CameraEngine implements
     @SuppressWarnings("WeakerAccess") protected boolean mPictureSnapshotMetering;
     @SuppressWarnings("WeakerAccess") protected float mPreviewFrameRate;
 
-    // Can be private
+    private WorkerHandler mHandler;
     @VisibleForTesting Handler mCrashHandler;
     private final FrameManager mFrameManager;
     private final Angles mAngles;
@@ -193,36 +171,42 @@ public abstract class CameraEngine implements
     private int mAudioBitRate;
     private boolean mHasFrameProcessors;
     private long mAutoFocusResetDelayMillis;
-    // in REF_VIEW, for consistency with SizeSelectors
+    private int mSnapshotMaxWidth = Integer.MAX_VALUE; // in REF_VIEW like SizeSelectors
-    private int mSnapshotMaxWidth = Integer.MAX_VALUE;
+    private int mSnapshotMaxHeight = Integer.MAX_VALUE; // in REF_VIEW like SizeSelectors
-    // in REF_VIEW, for consistency with SizeSelectors
-    private int mSnapshotMaxHeight = Integer.MAX_VALUE;
     private Overlay overlay;
 
-    // Steps
+    @SuppressWarnings("WeakerAccess")
-    private final Step.Callback mStepCallback = new Step.Callback() {
+    protected final CameraStateOrchestrator mOrchestrator
-        @Override @NonNull public Executor getExecutor() { return mHandler.getExecutor(); }
+            = new CameraStateOrchestrator(new CameraOrchestrator.Callback() {
-        @Override public void handleException(@NonNull Exception exception) {
+        @Override
-            CameraEngine.this.handleException(Thread.currentThread(), exception, false);
+        @NonNull
+        public WorkerHandler getJobWorker(@NonNull String job) {
+            return mHandler;
+        }
+
+        @Override
+        public void handleJobException(@NonNull String job, @NonNull Exception exception) {
+            handleException(Thread.currentThread(), exception, false);
         }
-    };
+    });
-    @VisibleForTesting
-    Step mEngineStep = new Step("engine", mStepCallback);
-    private Step mBindStep = new Step("bind", mStepCallback);
-    private Step mPreviewStep = new Step("preview", mStepCallback);
-    private Step mAllStep = new Step("all", mStepCallback);
 
     // Ops used for testing.
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mZoomOp = new Op<>();
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mZoomTask
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mExposureCorrectionOp
+            = Tasks.forResult(null);
-            = new Op<>();
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mExposureCorrectionTask
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mFlashOp = new Op<>();
+            = Tasks.forResult(null);
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mWhiteBalanceOp
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mFlashTask
-            = new Op<>();
+            = Tasks.forResult(null);
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mHdrOp = new Op<>();
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mWhiteBalanceTask
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mLocationOp = new Op<>();
+            = Tasks.forResult(null);
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mPlaySoundsOp = new Op<>();
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mHdrTask
-    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Op<Void> mPreviewFrameRateOp = new Op<>();
+            = Tasks.forResult(null);
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mLocationTask
+            = Tasks.forResult(null);
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mPlaySoundsTask
+            = Tasks.forResult(null);
+    @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED) Task<Void> mPreviewFrameRateTask
+            = Tasks.forResult(null);
 
     protected CameraEngine(@NonNull Callback callback) {
         mCallback = callback;
@@ -252,7 +236,7 @@ public abstract class CameraEngine implements
      */
     private class CrashExceptionHandler implements Thread.UncaughtExceptionHandler {
         @Override
-        public void uncaughtException(final Thread thread, final Throwable throwable) {
+        public void uncaughtException(@NonNull Thread thread, @NonNull Throwable throwable) {
             handleException(thread, throwable, true);
         }
     }
@@ -263,7 +247,7 @@ public abstract class CameraEngine implements
      */
     private static class NoOpExceptionHandler implements Thread.UncaughtExceptionHandler {
         @Override
-        public void uncaughtException(Thread t, Throwable e) {
+        public void uncaughtException(@NonNull Thread thread, @NonNull Throwable throwable) {
             // No-op.
         }
     }
@@ -305,7 +289,7 @@ public abstract class CameraEngine implements
 
         final CameraException cameraException = (CameraException) throwable;
         LOG.e("uncaughtException:", "Got CameraException:", cameraException,
-                "on engine state:", getEngineState());
+                "on state:", getState());
         if (fromExceptionHandler) {
             // Got to restart the handler.
             thread.interrupt();
@@ -322,49 +306,95 @@ public abstract class CameraEngine implements
 
     //endregion
 
-    //region states and steps
+    //region State management
 
-    public final int getEngineState() {
+    @NonNull
-        return mEngineStep.getState();
+    public final CameraState getState() {
+        return mOrchestrator.getCurrentState();
     }
 
-    @SuppressWarnings("WeakerAccess")
+    @NonNull
-    public final int getBindState() {
+    public final CameraState getTargetState() {
-        return mBindStep.getState();
+        return mOrchestrator.getTargetState();
     }
 
-    @SuppressWarnings({"unused", "WeakerAccess"})
+    public boolean isChangingState() {
-    public final int getPreviewState() {
+        return mOrchestrator.hasPendingStateChange();
-        return mPreviewStep.getState();
     }
 
-    private boolean canStartEngine() {
+    /**
-        return mEngineStep.isStoppingOrStopped();
+     * Calls {@link #stop(boolean)} and waits for it.
+     * Not final due to mockito requirements.
+     *
+     * NOTE: Should not be called on the orchestrator thread! This would cause deadlocks due to us
+     * awaiting for {@link #stop(boolean)} to return.
+     */
+    public void destroy() {
+        LOG.i("DESTROY:", "state:", getState(), "thread:", Thread.currentThread());
+        // Prevent CameraEngine leaks. Don't set to null, or exceptions
+        // inside the standard stop() method might crash the main thread.
+        mHandler.getThread().setUncaughtExceptionHandler(new NoOpExceptionHandler());
+        // Stop if needed, synchronously and silently.
+        // Cannot use Tasks.await() because we might be on the UI thread.
+        final CountDownLatch latch = new CountDownLatch(1);
+        stop(true).addOnCompleteListener(
+                WorkerHandler.get().getExecutor(),
+                new OnCompleteListener<Void>() {
+            @Override
+            public void onComplete(@NonNull Task<Void> task) {
+                latch.countDown();
+            }
+        });
+        try {
+            boolean success = latch.await(3, TimeUnit.SECONDS);
+            if (!success) {
+                LOG.e("Probably some deadlock in destroy.",
+                        "Current thread:", Thread.currentThread(),
+                        "Handler thread: ", mHandler.getThread());
+            }
+        } catch (InterruptedException ignore) {}
     }
 
-    private boolean needsStopEngine() {
+    @SuppressWarnings("WeakerAccess")
-        return mEngineStep.isStartedOrStarting();
+    public void restart() {
+        LOG.i("RESTART:", "scheduled. State:", getState());
+        stop(false);
+        start();
     }
 
-    private boolean canStartBind() {
+    @NonNull
-        return mEngineStep.isStarted()
+    public Task<Void> start() {
-                && mPreview != null
+        LOG.i("START:", "scheduled. State:", getState());
-                && mPreview.hasSurface()
+        Task<Void> engine = startEngine();
-                && mBindStep.isStoppingOrStopped();
+        startBind();
+        startPreview();
+        return engine;
     }
 
-    private boolean needsStopBind() {
+    @NonNull
-        return mBindStep.isStartedOrStarting();
+    public Task<Void> stop(final boolean swallowExceptions) {
+        LOG.i("STOP:", "scheduled. State:", getState());
+        stopPreview(swallowExceptions);
+        stopBind(swallowExceptions);
+        return stopEngine(swallowExceptions);
     }
 
-    private boolean canStartPreview() {
+    @SuppressWarnings("WeakerAccess")
-        return mEngineStep.isStarted()
+    @NonNull
-                && mBindStep.isStarted()
+    protected Task<Void> restartBind() {
-                && mPreviewStep.isStoppingOrStopped();
+        LOG.i("RESTART BIND:", "scheduled. State:", getState());
+        stopPreview(false);
+        stopBind(false);
+        startBind();
+        return startPreview();
     }
 
-    private boolean needsStopPreview() {
+    @SuppressWarnings("WeakerAccess")
-        return mPreviewStep.isStartedOrStarting();
+    @NonNull
+    protected Task<Void> restartPreview() {
+        LOG.i("RESTART PREVIEW:", "scheduled. State:", getState());
+        stopPreview(false);
+        return startPreview();
     }
 
     //endregion
@@ -374,8 +404,9 @@ public abstract class CameraEngine implements
     @NonNull
     @EngineThread
     private Task<Void> startEngine() {
-        if (canStartEngine()) {
+        return mOrchestrator.scheduleStateChange(CameraState.OFF, CameraState.ENGINE,
-            mEngineStep.doStart(false, new Callable<Task<Void>>() {
+                true,
+                new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
                 if (!collectCameraInfo(mFacing)) {
@@ -384,34 +415,31 @@ public abstract class CameraEngine implements
                 }
                 return onStartEngine();
             }
-            }, new Runnable() {
+        }).addOnSuccessListener(new OnSuccessListener<Void>() {
             @Override
-                public void run() {
+            public void onSuccess(Void aVoid) {
                 mCallback.dispatchOnCameraOpened(mCameraOptions);
             }
         });
     }
-        return mEngineStep.getTask();
-    }
 
     @NonNull
     @EngineThread
     private Task<Void> stopEngine(boolean swallowExceptions) {
-        if (needsStopEngine()) {
+        return mOrchestrator.scheduleStateChange(CameraState.ENGINE, CameraState.OFF,
-            mEngineStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
+                !swallowExceptions,
+                new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
                 return onStopEngine();
             }
-            }, new Runnable() {
+        }).addOnSuccessListener(new OnSuccessListener<Void>() {
             @Override
-                public void run() {
+            public void onSuccess(Void aVoid) {
                 mCallback.dispatchOnCameraClosed();
             }
         });
     }
-        return mEngineStep.getTask();
-    }
 
     /**
      * Starts the engine.
@@ -438,30 +466,33 @@ public abstract class CameraEngine implements
     @NonNull
     @EngineThread
     private Task<Void> startBind() {
-        if (canStartBind()) {
+        return mOrchestrator.scheduleStateChange(CameraState.ENGINE, CameraState.BIND,
-            mBindStep.doStart(false, new Callable<Task<Void>>() {
+                true,
+                new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
+                if (mPreview != null && mPreview.hasSurface()) {
                     return onStartBind();
+                } else {
+                    return Tasks.forCanceled();
                 }
-            });
             }
-        return mBindStep.getTask();
+        });
     }
 
+    @SuppressWarnings("UnusedReturnValue")
     @NonNull
     @EngineThread
     private Task<Void> stopBind(boolean swallowExceptions) {
-        if (needsStopBind()) {
+        return mOrchestrator.scheduleStateChange(CameraState.BIND, CameraState.ENGINE,
-            mBindStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
+                !swallowExceptions,
+                new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
                 return onStopBind();
             }
         });
     }
-        return mBindStep.getTask();
-    }
 
     /**
      * Starts the binding process.
@@ -481,39 +512,6 @@ public abstract class CameraEngine implements
     @EngineThread
     protected abstract Task<Void> onStopBind();
 
-    @SuppressWarnings("WeakerAccess")
-    protected void restartBind() {
-        LOG.i("restartBind", "posting.");
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                LOG.w("restartBind", "executing stopPreview.");
-                stopPreview(false).continueWithTask(mHandler.getExecutor(),
-                        new Continuation<Void, Task<Void>>() {
-                    @Override
-                    public Task<Void> then(@NonNull Task<Void> task) {
-                        LOG.w("restartBind", "executing stopBind.");
-                        return stopBind(false);
-                    }
-                }).onSuccessTask(mHandler.getExecutor(), new SuccessContinuation<Void, Void>() {
-                    @NonNull
-                    @Override
-                    public Task<Void> then(@Nullable Void aVoid) {
-                        LOG.w("restartBind", "executing startBind.");
-                        return startBind();
-                    }
-                }).onSuccessTask(mHandler.getExecutor(), new SuccessContinuation<Void, Void>() {
-                    @NonNull
-                    @Override
-                    public Task<Void> then(@Nullable Void aVoid) {
-                        LOG.w("restartBind", "executing startPreview.");
-                        return startPreview();
-                    }
-                });
-            }
-        });
-    }
-
     //endregion
 
     //region Start & Stop preview
@@ -521,47 +519,29 @@ public abstract class CameraEngine implements
     @NonNull
     @EngineThread
     private Task<Void> startPreview() {
-        LOG.i("startPreview", "canStartPreview:", canStartPreview());
+        return mOrchestrator.scheduleStateChange(CameraState.BIND, CameraState.PREVIEW,
-        if (canStartPreview()) {
+                true,
-            mPreviewStep.doStart(false, new Callable<Task<Void>>() {
+                new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
                 return onStartPreview();
             }
         });
     }
-        return mPreviewStep.getTask();
-    }
 
+    @SuppressWarnings("UnusedReturnValue")
     @NonNull
     @EngineThread
     private Task<Void> stopPreview(boolean swallowExceptions) {
-        LOG.i("stopPreview",
+        return mOrchestrator.scheduleStateChange(CameraState.PREVIEW, CameraState.BIND,
-                "needsStopPreview:", needsStopPreview(),
+                !swallowExceptions,
-                "swallowExceptions:", swallowExceptions);
+                new Callable<Task<Void>>() {
-        if (needsStopPreview()) {
-            mPreviewStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
             @Override
             public Task<Void> call() {
                 return onStopPreview();
             }
         });
     }
-        return mPreviewStep.getTask();
-    }
-
-    @SuppressWarnings("WeakerAccess")
-    protected void restartPreview() {
-        LOG.i("restartPreview", "posting.");
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                LOG.i("restartPreview", "executing.");
-                stopPreview(false);
-                startPreview();
-            }
-        });
-    }
 
     /**
      * Starts the preview streaming.
@@ -592,33 +572,24 @@ public abstract class CameraEngine implements
     @Override
     public final void onSurfaceAvailable() {
         LOG.i("onSurfaceAvailable:", "Size is", getPreviewSurfaceSize(Reference.VIEW));
-        mHandler.run(new Runnable() {
+        startBind();
-            @Override
+        startPreview();
-            public void run() {
-                startBind().onSuccessTask(mHandler.getExecutor(), new SuccessContinuation<Void, Void>() {
-                    @NonNull
-                    @Override
-                    public Task<Void> then(@Nullable Void aVoid) {
-                        return startPreview();
-                    }
-                });
     }
-        });
+
+    @Override
+    public final void onSurfaceDestroyed() {
+        LOG.i("onSurfaceDestroyed");
+        stopPreview(false);
+        stopBind(false);
     }
 
     @Override
     public final void onSurfaceChanged() {
-        LOG.i("onSurfaceChanged:", "Size is", getPreviewSurfaceSize(Reference.VIEW),
+        LOG.i("onSurfaceChanged:", "Size is", getPreviewSurfaceSize(Reference.VIEW));
-                "Posting.");
+        mOrchestrator.scheduleStateful("surface changed", CameraState.BIND,
-        mHandler.run(new Runnable() {
+                new Runnable() {
             @Override
             public void run() {
-                LOG.i("onSurfaceChanged:",
-                        "Engine started?", mEngineStep.isStarted(),
-                        "Bind started?", mBindStep.isStarted());
-                if (!mEngineStep.isStarted()) return; // Too early
-                if (!mBindStep.isStarted()) return; // Too early
-
                 // Compute a new camera preview size and apply.
                 Size newSize = computePreviewStreamSize();
                 if (newSize.equals(mPreviewStreamSize)) {
@@ -643,176 +614,6 @@ public abstract class CameraEngine implements
     @EngineThread
     protected abstract void onPreviewStreamSizeChanged();
 
-    @Override
-    public final void onSurfaceDestroyed() {
-        LOG.i("onSurfaceDestroyed");
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                stopPreview(false).onSuccessTask(mHandler.getExecutor(),
-                        new SuccessContinuation<Void, Void>() {
-                    @NonNull
-                    @Override
-                    public Task<Void> then(@Nullable Void aVoid) {
-                        return stopBind(false);
-                    }
-                });
-            }
-        });
-    }
-
-    //endregion
-
-    //region Start & Stop all
-
-    /**
-     * Not final due to mockito requirements, but this is basically
-     * it, nothing more to do.
-     *
-     * NOTE: Should not be called on the {@link #mHandler} thread! I think
-     * that would cause deadlocks due to us awaiting for {@link #stop()} to return.
-     */
-    public void destroy() {
-        LOG.i("destroy:", "state:", getEngineState(), "thread:", Thread.currentThread());
-        // Prevent CameraEngine leaks. Don't set to null, or exceptions
-        // inside the standard stop() method might crash the main thread.
-        mHandler.getThread().setUncaughtExceptionHandler(new NoOpExceptionHandler());
-        // Stop if needed, synchronously and silently.
-        // Cannot use Tasks.await() because we might be on the UI thread.
-        final CountDownLatch latch = new CountDownLatch(1);
-        stop(true).addOnCompleteListener(mHandler.getExecutor(),
-                new OnCompleteListener<Void>() {
-            @Override
-            public void onComplete(@NonNull Task<Void> task) {
-                latch.countDown();
-            }
-        });
-        try {
-            boolean success = latch.await(3, TimeUnit.SECONDS);
-            if (!success) {
-                // TODO seems like this is always the case?
-                LOG.e("Probably some deadlock in destroy.",
-                        "Current thread:", Thread.currentThread(),
-                        "Handler thread: ", mHandler.getThread());
-            }
-        } catch (InterruptedException ignore) {}
-    }
-
-    @SuppressWarnings("WeakerAccess")
-    protected final void restart() {
-        LOG.i("Restart:", "calling stop and start");
-        stop();
-        start();
-    }
-
-    @NonNull
-    public Task<Void> start() {
-        LOG.i("Start:", "posting runnable. State:", getEngineState());
-        final TaskCompletionSource<Void> outTask = new TaskCompletionSource<>();
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                LOG.w("Start:", "executing runnable. AllState is", mAllStep.getState());
-                // It's better to schedule anyway. allStep might be STARTING and we might be
-                // tempted to early return here, but the truth is that there might be a stop
-                // already scheduled when the STARTING op ends.
-                // if (mAllStep.isStoppingOrStopped()) {
-                //     LOG.i("Start:", "executing runnable. AllState is STOPPING or STOPPED,
-                //     so we schedule a start.");
-                    mAllStep.doStart(false, new Callable<Task<Void>>() {
-                        @Override
-                        public Task<Void> call() {
-                            return startEngine().addOnFailureListener(mHandler.getExecutor(),
-                                    new OnFailureListener() {
-                                @Override
-                                public void onFailure(@NonNull Exception e) {
-                                    outTask.trySetException(e);
-                                }
-                            }).onSuccessTask(mHandler.getExecutor(), new SuccessContinuation<Void, Void>() {
-                                @NonNull
-                                @Override
-                                public Task<Void> then(@Nullable Void aVoid) {
-                                    outTask.trySetResult(null);
-                                    return startBind();
-                                }
-                            }).onSuccessTask(mHandler.getExecutor(), new SuccessContinuation<Void, Void>() {
-                                @NonNull
-                                @Override
-                                public Task<Void> then(@Nullable Void aVoid) {
-                                    return startPreview();
-                                }
-                            });
-                        }
-                    });
-                // } else {
-                //     // NOTE: this returns early if we were STARTING.
-                //     LOG.i("Start:",
-                //     "executing runnable. AllState is STARTING or STARTED, so we return early.");
-                //     outTask.trySetResult(null);
-                // }
-            }
-        });
-        return outTask.getTask();
-    }
-
-    @NonNull
-    public Task<Void> stop() {
-        return stop(false);
-    }
-
-    @NonNull
-    private Task<Void> stop(final boolean swallowExceptions) {
-        LOG.i("Stop:", "posting runnable. State:", getEngineState());
-        final TaskCompletionSource<Void> outTask = new TaskCompletionSource<>();
-        mHandler.run(new Runnable() {
-            @Override
-            public void run() {
-                LOG.w("Stop:", "executing runnable. AllState is", mAllStep.getState());
-                // It's better to schedule anyway. allStep might be STOPPING and we might be
-                // tempted to early return here, but the truth is that there might be a start
-                // already scheduled when the STOPPING op ends.
-                // if (mAllStep.isStartedOrStarting()) {
-                //     LOG.i("Stop:", "executing runnable. AllState is STARTING or STARTED,
-                //     so we schedule a stop.");
-                    mAllStep.doStop(swallowExceptions, new Callable<Task<Void>>() {
-                        @Override
-                        public Task<Void> call() {
-                            return stopPreview(swallowExceptions).continueWithTask(
-                                    mHandler.getExecutor(), new Continuation<Void, Task<Void>>() {
-                                @Override
-                                public Task<Void> then(@NonNull Task<Void> task) {
-                                    return stopBind(swallowExceptions);
-                                }
-                            }).continueWithTask(mHandler.getExecutor(), new Continuation<Void, Task<Void>>() {
-                                @Override
-                                public Task<Void> then(@NonNull Task<Void> task) {
-                                    return stopEngine(swallowExceptions);
-                                }
-                            }).continueWithTask(mHandler.getExecutor(), new Continuation<Void, Task<Void>>() {
-                                @Override
-                                public Task<Void> then(@NonNull Task<Void> task) {
-                                    if (task.isSuccessful()) {
-                                        outTask.trySetResult(null);
-                                    } else {
-                                        //noinspection ConstantConditions
-                                        outTask.trySetException(task.getException());
-                                    }
-                                    return task;
-                                }
-                            });
-                        }
-                    });
-                // } else {
-                //     // NOTE: this returns early if we were STOPPING.
-                //     LOG.i("Stop:", "executing runnable.
-                //     AllState is STOPPING or STOPPED, so we return early.");
-                //     outTask.trySetResult(null);
-                // }
-            }
-        });
-        return outTask.getTask();
-    }
-
     //endregion
 
     //region Final setters and getters
@@ -922,7 +723,7 @@ public abstract class CameraEngine implements
     }
 
     /**
-     * Sets a new facing value. This will restart the session (if there's any)
+     * Sets a new facing value. This will restart the engine session (if there's any)
      * so that we can open the new facing camera.
      * @param facing facing
      */
@@ -930,10 +731,10 @@ public abstract class CameraEngine implements
         final Facing old = mFacing;
         if (facing != old) {
             mFacing = facing;
-            mHandler.run(new Runnable() {
+            mOrchestrator.scheduleStateful("facing", CameraState.ENGINE,
+                    new Runnable() {
                 @Override
                 public void run() {
-                    if (getEngineState() < STATE_STARTED) return;
                     if (collectCameraInfo(facing)) {
                         restart();
                     } else {
@@ -975,13 +776,12 @@ public abstract class CameraEngine implements
     public final void setMode(@NonNull Mode mode) {
         if (mode != mMode) {
             mMode = mode;
-            mHandler.run(new Runnable() {
+            mOrchestrator.scheduleStateful("mode", CameraState.ENGINE,
+                    new Runnable() {
                 @Override
                 public void run() {
-                    if (getEngineState() == STATE_STARTED) {
                     restart();
                 }
-                }
             });
         }
     }
@@ -1134,22 +934,22 @@ public abstract class CameraEngine implements
 
     /* not final for tests */
     public void takePicture(final @NonNull PictureResult.Stub stub) {
-        LOG.i("takePicture", "scheduling");
+        // Save boolean before scheduling! See how Camera2Engine calls this with a temp value.
-        mHandler.run(new Runnable() {
+        final boolean metering = mPictureMetering;
+        mOrchestrator.scheduleStateful("take picture", CameraState.BIND,
+                new Runnable() {
             @Override
             public void run() {
-                LOG.i("takePicture", "performing. BindState:", getBindState(),
+                LOG.i("takePicture:", "running. isTakingPicture:", isTakingPicture());
-                        "isTakingPicture:", isTakingPicture());
+                if (isTakingPicture()) return;
                 if (mMode == Mode.VIDEO) {
                     throw new IllegalStateException("Can't take hq pictures while in VIDEO mode");
                 }
-                if (getBindState() < STATE_STARTED) return;
-                if (isTakingPicture()) return;
                 stub.isSnapshot = false;
                 stub.location = mLocation;
                 stub.facing = mFacing;
                 stub.format = mPictureFormat;
-                onTakePicture(stub, mPictureMetering);
+                onTakePicture(stub, metering);
             }
         });
     }
@@ -1160,13 +960,13 @@ public abstract class CameraEngine implements
      * @param stub a picture stub
      */
     public final void takePictureSnapshot(final @NonNull PictureResult.Stub stub) {
-        LOG.i("takePictureSnapshot", "scheduling");
+        // Save boolean before scheduling! See how Camera2Engine calls this with a temp value.
-        mHandler.run(new Runnable() {
+        final boolean metering = mPictureSnapshotMetering;
+        mOrchestrator.scheduleStateful("take picture snapshot", CameraState.BIND,
+                new Runnable() {
             @Override
             public void run() {
-                LOG.i("takePictureSnapshot", "performing. BindState:",
+                LOG.i("takePictureSnapshot:", "running. isTakingPicture:", isTakingPicture());
-                        getBindState(), "isTakingPicture:", isTakingPicture());
-                if (getBindState() < STATE_STARTED) return;
                 if (isTakingPicture()) return;
                 stub.location = mLocation;
                 stub.isSnapshot = true;
@@ -1175,7 +975,7 @@ public abstract class CameraEngine implements
                 // Leave the other parameters to subclasses.
                 //noinspection ConstantConditions
                 AspectRatio ratio = AspectRatio.of(getPreviewSurfaceSize(Reference.OUTPUT));
-                onTakePictureSnapshot(stub, ratio, mPictureSnapshotMetering);
+                onTakePictureSnapshot(stub, ratio, metering);
             }
         });
     }
@@ -1202,13 +1002,10 @@ public abstract class CameraEngine implements
     }
 
     public final void takeVideo(final @NonNull VideoResult.Stub stub, final @NonNull File file) {
-        LOG.i("takeVideo", "scheduling");
+        mOrchestrator.scheduleStateful("take video", CameraState.BIND, new Runnable() {
-        mHandler.run(new Runnable() {
             @Override
             public void run() {
-                LOG.i("takeVideo", "performing. BindState:", getBindState(),
+                LOG.i("takeVideo:", "running. isTakingVideo:", isTakingVideo());
-                        "isTakingVideo:", isTakingVideo());
-                if (getBindState() < STATE_STARTED) return;
                 if (isTakingVideo()) return;
                 if (mMode == Mode.PICTURE) {
                     throw new IllegalStateException("Can't record video while in PICTURE mode");
@@ -1234,14 +1031,11 @@ public abstract class CameraEngine implements
      */
     public final void takeVideoSnapshot(@NonNull final VideoResult.Stub stub,
                                         @NonNull final File file) {
-        LOG.i("takeVideoSnapshot", "scheduling");
+        mOrchestrator.scheduleStateful("take video snapshot", CameraState.BIND,
-        mHandler.run(new Runnable() {
+                new Runnable() {
             @Override
             public void run() {
-                LOG.i("takeVideoSnapshot", "performing. BindState:", getBindState(),
+                LOG.i("takeVideoSnapshot:", "running. isTakingVideo:", isTakingVideo());
-                        "isTakingVideo:", isTakingVideo());
-                if (getBindState() < STATE_STARTED) return;
-                if (isTakingVideo()) return;
                 stub.file = file;
                 stub.isSnapshot = true;
                 stub.videoCodec = mVideoCodec;
@@ -1260,11 +1054,10 @@ public abstract class CameraEngine implements
     }
 
     public final void stopVideo() {
-        LOG.i("stopVideo", "posting");
+        mOrchestrator.schedule("stop video", true, new Runnable() {
-        mHandler.run(new Runnable() {
             @Override
             public void run() {
-                LOG.i("stopVideo", "executing.", "isTakingVideo?", isTakingVideo());
+                LOG.i("stopVideo", "running. isTakingVideo?", isTakingVideo());
                 onStopVideo();
             }
         });

cameraview/src/main/java/com/otaliastudios/cameraview/engine/Step.java

@@ -1,178 +0,0 @@
-package com.otaliastudios.cameraview.engine;
-
-import com.google.android.gms.tasks.Continuation;
-import com.google.android.gms.tasks.OnFailureListener;
-import com.google.android.gms.tasks.SuccessContinuation;
-import com.google.android.gms.tasks.Task;
-import com.google.android.gms.tasks.Tasks;
-import com.otaliastudios.cameraview.CameraLogger;
-
-import java.util.concurrent.Callable;
-import java.util.concurrent.Executor;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-import androidx.annotation.VisibleForTesting;
-
-/**
- * Represents one of the steps in the {@link CameraEngine} setup: for example, the engine step,
- * the bind-to-surface step, and the preview step.
- *
- * A step is something that can be setup (started) or torn down (stopped), and
- * steps can of course depend onto each other.
- *
- * The purpose of this class is to manage the step state (stopping, stopped, starting or started)
- * and, more importantly, to perform START and STOP operations in such a way that they do not
- * overlap. For example, if we're stopping, we're wait for stop to finish before starting again.
- *
- * This is an important condition for simplifying the engine code.
- * Since Camera1, the only requirement was basically to use a single thread.
- * Since Camera2, which has an asynchronous API, further care must be used.
- *
- * For this reason, we use Google's {@link Task} abstraction and only start new operations
- * once the previous one has ended.
- *
- * <strong>This class is NOT thread safe!</string>
- */
-class Step {
-
-    private static final String TAG = Step.class.getSimpleName();
-    private static final CameraLogger LOG = CameraLogger.create(TAG);
-
-    interface Callback {
-        @NonNull
-        Executor getExecutor();
-        void handleException(@NonNull Exception exception);
-    }
-
-    static final int STATE_STOPPING = -1;
-    static final int STATE_STOPPED = 0;
-    static final int STATE_STARTING = 1;
-    static final int STATE_STARTED = 2;
-
-    private int state = STATE_STOPPED;
-
-    // To avoid dirty scenarios (e.g. calling stopXXX while XXX is starting),
-    // and since every operation can be asynchronous, we use some tasks for each step.
-    private Task<Void> task = Tasks.forResult(null);
-
-    private final String name;
-    private final Callback callback;
-
-    Step(@NonNull String name, @NonNull Callback callback) {
-        this.name = name.toUpperCase();
-        this.callback = callback;
-    }
-
-    int getState() {
-        return state;
-    }
-
-    @VisibleForTesting void setState(int newState) {
-        state = newState;
-    }
-
-    @NonNull
-    String getStateName() {
-        switch (state) {
-            case STATE_STOPPING: return name + "_STATE_STOPPING";
-            case STATE_STOPPED: return name + "_STATE_STOPPED";
-            case STATE_STARTING: return name + "_STATE_STARTING";
-            case STATE_STARTED: return name + "_STATE_STARTED";
-        }
-        return "null";
-    }
-
-    boolean isStoppingOrStopped() {
-        return state == STATE_STOPPING || state == STATE_STOPPED;
-    }
-
-    boolean isStartedOrStarting() {
-        return state == STATE_STARTING || state == STATE_STARTED;
-    }
-
-    boolean isStarted() {
-        return state == STATE_STARTED;
-    }
-
-    @NonNull
-    Task<Void> getTask() {
-        return task;
-    }
-
-    @SuppressWarnings({"SameParameterValue", "UnusedReturnValue"})
-    Task<Void> doStart(final boolean swallowExceptions, final @NonNull Callable<Task<Void>> op) {
-        return doStart(swallowExceptions, op, null);
-    }
-
-    Task<Void> doStart(final boolean swallowExceptions,
-                       final @NonNull Callable<Task<Void>> op,
-                       final @Nullable Runnable onStarted) {
-        LOG.i(name, "doStart", "Called. Enqueuing.");
-        task = task.continueWithTask(callback.getExecutor(), new Continuation<Void, Task<Void>>() {
-            @Override
-            public Task<Void> then(@NonNull Task<Void> task) throws Exception {
-                LOG.i(name, "doStart", "About to start. Setting state to STARTING");
-                setState(STATE_STARTING);
-                return op.call().addOnFailureListener(callback.getExecutor(),
-                        new OnFailureListener() {
-                    @Override
-                    public void onFailure(@NonNull Exception e) {
-                        LOG.w(name, "doStart", "Failed with error", e,
-                                "Setting state to STOPPED");
-                        setState(STATE_STOPPED);
-                        if (!swallowExceptions) callback.handleException(e);
-                    }
-                });
-            }
-        }).onSuccessTask(callback.getExecutor(), new SuccessContinuation<Void, Void>() {
-            @NonNull
-            @Override
-            public Task<Void> then(@Nullable Void aVoid) {
-                LOG.i(name, "doStart", "Succeeded! Setting state to STARTED");
-                setState(STATE_STARTED);
-                if (onStarted != null) onStarted.run();
-                return Tasks.forResult(null);
-            }
-        });
-        return task;
-    }
-
-    @SuppressWarnings("UnusedReturnValue")
-    Task<Void> doStop(final boolean swallowExceptions, final @NonNull Callable<Task<Void>> op) {
-        return doStop(swallowExceptions, op, null);
-    }
-
-    Task<Void> doStop(final boolean swallowExceptions,
-                      final @NonNull Callable<Task<Void>> op,
-                      final @Nullable Runnable onStopped) {
-        LOG.i(name, "doStop", "Called. Enqueuing.");
-        task = task.continueWithTask(callback.getExecutor(), new Continuation<Void, Task<Void>>() {
-            @Override
-            public Task<Void> then(@NonNull Task<Void> task) throws Exception {
-                LOG.i(name, "doStop", "About to stop. Setting state to STOPPING");
-                state = STATE_STOPPING;
-                return op.call().addOnFailureListener(callback.getExecutor(),
-                        new OnFailureListener() {
-                    @Override
-                    public void onFailure(@NonNull Exception e) {
-                        LOG.w(name, "doStop", "Failed with error", e,
-                                "Setting state to STOPPED");
-                        state = STATE_STOPPED;
-                        if (!swallowExceptions) callback.handleException(e);
-                    }
-                });
-            }
-        }).onSuccessTask(callback.getExecutor(), new SuccessContinuation<Void, Void>() {
-            @NonNull
-            @Override
-            public Task<Void> then(@Nullable Void aVoid) {
-                LOG.i(name, "doStop", "Succeeded! Setting state to STOPPED");
-                state = STATE_STOPPED;
-                if (onStopped != null) onStopped.run();
-                return Tasks.forResult(null);
-            }
-        });
-        return task;
-    }
-}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/BaseAction.java

@@ -39,6 +39,7 @@ public abstract class BaseAction implements Action {
 
     @Override
     public final void start(@NonNull ActionHolder holder) {
+        this.holder = holder;
         holder.addAction(this);
         if (holder.getLastResult(this) != null) {
             onStart(holder);
@@ -64,6 +65,8 @@ public abstract class BaseAction implements Action {
      */
     @CallSuper
     protected void onStart(@NonNull ActionHolder holder) {
+        // Repeating holder assignment here (already in start()) because we NEED it in start()
+        // but some special actions will not call start() at all for their children.
         this.holder = holder;
         // Overrideable
     }

cameraview/src/main/java/com/otaliastudios/cameraview/engine/action/LogAction.java

@@ -1,4 +1,4 @@
-package com.otaliastudios.cameraview.engine;
+package com.otaliastudios.cameraview.engine.action;
 
 import android.hardware.camera2.CaptureRequest;
 import android.hardware.camera2.CaptureResult;
@@ -9,11 +9,12 @@ import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 
 import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.engine.Camera2Engine;
 import com.otaliastudios.cameraview.engine.action.ActionHolder;
 import com.otaliastudios.cameraview.engine.action.BaseAction;
 
 @RequiresApi(Build.VERSION_CODES.LOLLIPOP)
-class LogAction extends BaseAction {
+public class LogAction extends BaseAction {
 
     private final static CameraLogger LOG
             = CameraLogger.create(Camera2Engine.class.getSimpleName());

cameraview/src/main/java/com/otaliastudios/cameraview/engine/orchestrator/CameraOrchestrator.java

@@ -0,0 +1,183 @@
+package com.otaliastudios.cameraview.engine.orchestrator;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.google.android.gms.tasks.OnCompleteListener;
+import com.google.android.gms.tasks.Task;
+import com.google.android.gms.tasks.TaskCompletionSource;
+import com.google.android.gms.tasks.Tasks;
+import com.otaliastudios.cameraview.CameraLogger;
+import com.otaliastudios.cameraview.internal.utils.WorkerHandler;
+
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CancellationException;
+
+/**
+ * Schedules {@link com.otaliastudios.cameraview.engine.CameraEngine} actions,
+ * so that they always run on the same thread.
+ *
+ * We need to be extra careful (not as easy as posting on a Handler) because the engine
+ * has different states, and some actions will modify the engine state - turn it on or
+ * tear it down. Other actions might need a specific state to be executed.
+ * And most importantly, some actions will finish asynchronously, so subsequent actions
+ * should wait for the previous to finish, but without blocking the thread.
+ */
+@SuppressWarnings("WeakerAccess")
+public class CameraOrchestrator {
+
+    protected static final String TAG = CameraOrchestrator.class.getSimpleName();
+    protected static final CameraLogger LOG = CameraLogger.create(TAG);
+
+    public interface Callback {
+        @NonNull
+        WorkerHandler getJobWorker(@NonNull String job);
+        void handleJobException(@NonNull String job, @NonNull Exception exception);
+    }
+
+    protected static class Token {
+        public final String name;
+        public final Task<Void> task;
+
+        private Token(@NonNull String name, @NonNull Task<Void> task) {
+            this.name = name;
+            this.task = task;
+        }
+
+        @Override
+        public boolean equals(@Nullable Object obj) {
+            return obj instanceof Token && ((Token) obj).name.equals(name);
+        }
+    }
+
+    protected final Callback mCallback;
+    protected final ArrayDeque<Token> mJobs = new ArrayDeque<>();
+    protected final Object mLock = new Object();
+    private final Map<String, Runnable> mDelayedJobs = new HashMap<>();
+
+    public CameraOrchestrator(@NonNull Callback callback) {
+        mCallback = callback;
+        ensureToken();
+    }
+
+    @NonNull
+    public Task<Void> schedule(@NonNull String name,
+                               boolean dispatchExceptions,
+                               @NonNull final Runnable job) {
+        return schedule(name, dispatchExceptions, new Callable<Task<Void>>() {
+            @Override
+            public Task<Void> call() {
+                job.run();
+                return Tasks.forResult(null);
+            }
+        });
+    }
+
+    @NonNull
+    public Task<Void> schedule(@NonNull final String name,
+                               final boolean dispatchExceptions,
+                               @NonNull final Callable<Task<Void>> job) {
+        LOG.i(name.toUpperCase(), "- Scheduling.");
+        final TaskCompletionSource<Void> source = new TaskCompletionSource<>();
+        final WorkerHandler handler = mCallback.getJobWorker(name);
+        synchronized (mLock) {
+            applyCompletionListener(mJobs.getLast().task, handler,
+                    new OnCompleteListener<Void>() {
+                @Override
+                public void onComplete(@NonNull Task<Void> task) {
+                    synchronized (mLock) {
+                        mJobs.removeFirst();
+                        ensureToken();
+                    }
+                    try {
+                        LOG.i(name.toUpperCase(), "- Executing.");
+                        Task<Void> inner = job.call();
+                        applyCompletionListener(inner, handler, new OnCompleteListener<Void>() {
+                            @Override
+                            public void onComplete(@NonNull Task<Void> task) {
+                                Exception e = task.getException();
+                                LOG.i(name.toUpperCase(), "- Finished.", e);
+                                if (e != null) {
+                                    if (dispatchExceptions) {
+                                        mCallback.handleJobException(name, e);
+                                    }
+                                    source.trySetException(e);
+                                } else if (task.isCanceled()) {
+                                    source.trySetException(new CancellationException());
+                                } else {
+                                    source.trySetResult(null);
+                                }
+                            }
+                        });
+                    } catch (Exception e) {
+                        LOG.i(name.toUpperCase(), "- Finished.", e);
+                        if (dispatchExceptions) mCallback.handleJobException(name, e);
+                        source.trySetException(e);
+                    }
+                }
+            });
+            mJobs.addLast(new Token(name, source.getTask()));
+        }
+        return source.getTask();
+    }
+
+    public void scheduleDelayed(@NonNull final String name,
+                                long minDelay,
+                                @NonNull final Runnable runnable) {
+        Runnable wrapper = new Runnable() {
+            @Override
+            public void run() {
+                schedule(name, true, runnable);
+                synchronized (mLock) {
+                    if (mDelayedJobs.containsValue(this)) {
+                        mDelayedJobs.remove(name);
+                    }
+                }
+            }
+        };
+        synchronized (mLock) {
+            mDelayedJobs.put(name, wrapper);
+            mCallback.getJobWorker(name).post(minDelay, wrapper);
+        }
+    }
+
+    public void remove(@NonNull String name) {
+        synchronized (mLock) {
+            if (mDelayedJobs.get(name) != null) {
+                //noinspection ConstantConditions
+                mCallback.getJobWorker(name).remove(mDelayedJobs.get(name));
+                mDelayedJobs.remove(name);
+            }
+            Token token = new Token(name, Tasks.<Void>forResult(null));
+            //noinspection StatementWithEmptyBody
+            while (mJobs.remove(token)) { /* do nothing */ }
+            ensureToken();
+        }
+    }
+
+    private void ensureToken() {
+        synchronized (mLock) {
+            if (mJobs.isEmpty()) {
+                mJobs.add(new Token("BASE", Tasks.<Void>forResult(null)));
+            }
+        }
+    }
+
+    private static void applyCompletionListener(@NonNull final Task<Void> task,
+                                                @NonNull WorkerHandler handler,
+                                                @NonNull final OnCompleteListener<Void> listener) {
+        if (task.isComplete()) {
+            handler.run(new Runnable() {
+                @Override
+                public void run() {
+                    listener.onComplete(task);
+                }
+            });
+        } else {
+            task.addOnCompleteListener(handler.getExecutor(), listener);
+        }
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/orchestrator/CameraState.java

@@ -0,0 +1,17 @@
+package com.otaliastudios.cameraview.engine.orchestrator;
+
+import androidx.annotation.NonNull;
+
+public enum CameraState {
+    OFF(0), ENGINE(1), BIND(2), PREVIEW(3);
+
+    private int mState;
+
+    CameraState(int state) {
+        mState = state;
+    }
+
+    public boolean isAtLeast(@NonNull CameraState reference) {
+        return mState >= reference.mState;
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/engine/orchestrator/CameraStateOrchestrator.java

@@ -0,0 +1,117 @@
+package com.otaliastudios.cameraview.engine.orchestrator;
+
+import androidx.annotation.NonNull;
+
+import com.google.android.gms.tasks.Continuation;
+import com.google.android.gms.tasks.OnCompleteListener;
+import com.google.android.gms.tasks.Task;
+import com.google.android.gms.tasks.Tasks;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executor;
+
+/**
+ * A special {@link CameraOrchestrator} with special methods that deal with the
+ * {@link CameraState}.
+ */
+public class CameraStateOrchestrator extends CameraOrchestrator {
+
+    private CameraState mCurrentState = CameraState.OFF;
+    private CameraState mTargetState = CameraState.OFF;
+    private int mStateChangeCount = 0;
+
+    public CameraStateOrchestrator(@NonNull Callback callback) {
+        super(callback);
+    }
+
+    @NonNull
+    public CameraState getCurrentState() {
+        return mCurrentState;
+    }
+
+    @NonNull
+    public CameraState getTargetState() {
+        return mTargetState;
+    }
+
+    public boolean hasPendingStateChange() {
+        synchronized (mLock) {
+            for (Token token : mJobs) {
+                if (token.name.contains(" > ") && !token.task.isComplete()) {
+                    return true;
+                }
+            }
+            return false;
+        }
+    }
+
+    @NonNull
+    public Task<Void> scheduleStateChange(@NonNull final CameraState fromState,
+                                          @NonNull final CameraState toState,
+                                          boolean dispatchExceptions,
+                                          @NonNull final Callable<Task<Void>> stateChange) {
+        final int changeCount = ++mStateChangeCount;
+        mTargetState = toState;
+
+        final boolean isTearDown = !toState.isAtLeast(fromState);
+        final String changeName = fromState.name() + " > " + toState.name();
+        return schedule(changeName, dispatchExceptions, new Callable<Task<Void>>() {
+            @Override
+            public Task<Void> call() throws Exception {
+                if (getCurrentState() != fromState) {
+                    LOG.w(changeName.toUpperCase(), "- State mismatch, aborting. current:",
+                            getCurrentState(), "from:", fromState, "to:", toState);
+                    return Tasks.forCanceled();
+                } else {
+                    Executor executor = mCallback.getJobWorker(changeName).getExecutor();
+                    return stateChange.call().continueWithTask(executor,
+                            new Continuation<Void, Task<Void>>() {
+                        @Override
+                        public Task<Void> then(@NonNull Task<Void> task) {
+                            if (task.isSuccessful() || isTearDown) {
+                                mCurrentState = toState;
+                            }
+                            return task;
+                        }
+                    });
+                }
+            }
+        }).addOnCompleteListener(new OnCompleteListener<Void>() {
+            @Override
+            public void onComplete(@NonNull Task<Void> task) {
+                if (changeCount == mStateChangeCount) {
+                    mTargetState = mCurrentState;
+                }
+            }
+        });
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    @NonNull
+    public Task<Void> scheduleStateful(@NonNull String name,
+                                       @NonNull final CameraState atLeast,
+                                       @NonNull final Runnable job) {
+        return schedule(name, true, new Runnable() {
+            @Override
+            public void run() {
+                if (getCurrentState().isAtLeast(atLeast)) {
+                    job.run();
+                }
+            }
+        });
+    }
+
+    public void scheduleStatefulDelayed(@NonNull String name,
+                                        @NonNull final CameraState atLeast,
+                                        long delay,
+                                        @NonNull final Runnable job) {
+        scheduleDelayed(name, delay, new Runnable() {
+            @Override
+            public void run() {
+                if (getCurrentState().isAtLeast(atLeast)) {
+                    job.run();
+                }
+            }
+        });
+    }
+}

cameraview/src/main/java/com/otaliastudios/cameraview/internal/GridLinesLayout.java

@@ -15,7 +15,6 @@ import android.util.TypedValue;
 import android.view.View;
 
 import com.otaliastudios.cameraview.controls.Grid;
-import com.otaliastudios.cameraview.internal.utils.Op;
 
 /**
  * A layout overlay that draws grid lines based on the {@link Grid} parameter.
@@ -32,8 +31,11 @@ public class GridLinesLayout extends View {
     private ColorDrawable vert;
     private final float width;
 
-    @VisibleForTesting
+    interface DrawCallback {
-    Op<Integer> drawOp = new Op<>();
+        void onDraw(int lines);
+    }
+
+    @VisibleForTesting DrawCallback callback;
 
     public GridLinesLayout(@NonNull Context context) {
         this(context, null);
@@ -117,7 +119,6 @@ public class GridLinesLayout extends View {
     @Override
     protected void onDraw(@NonNull Canvas canvas) {
         super.onDraw(canvas);
-        drawOp.start();
         int count = getLineCount();
         for (int n = 0; n < count; n++) {
             float pos = getLinePosition(n);
@@ -132,6 +133,8 @@ public class GridLinesLayout extends View {
             vert.draw(canvas);
             canvas.translate(- pos * getWidth(), 0);
         }
-        drawOp.end(count);
+        if (callback != null) {
+            callback.onDraw(count);
+        }
     }
 }

cameraview/src/main/java/com/otaliastudios/cameraview/internal/utils/Op.java

@@ -1,111 +0,0 @@
-package com.otaliastudios.cameraview.internal.utils;
-
-import androidx.annotation.NonNull;
-
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.TimeUnit;
-
-/**
- * A naive implementation of {@link java.util.concurrent.CountDownLatch}
- * to help in testing.
- */
-public class Op<T> {
-
-    private CountDownLatch mLatch;
-    private T mResult;
-    private int mCount;
-
-    /**
-     * Creates an empty task.
-     *
-     * Listeners should:
-     * - call {@link #listen()} to notify they are interested in the next action
-     * - call {@link #await()} to know when the action is performed.
-     *
-     * Op owners should:
-     * - call {@link #start()} when task started
-     * - call {@link #end(Object)} when task ends
-     */
-    public Op() { }
-
-    /**
-     * Creates an empty task and starts listening.
-     * @param startListening whether to call listen
-     */
-    public Op(boolean startListening) {
-        if (startListening) listen();
-    }
-
-    private boolean isListening() {
-        return mLatch != null;
-    }
-
-    /**
-     * Op owner method: notifies the action started.
-     */
-    public void start() {
-        if (!isListening()) mCount++;
-    }
-
-    /**
-     * Op owner method: notifies the action ended.
-     * @param result the action result
-     */
-    public void end(T result) {
-        if (mCount > 0) {
-            mCount--;
-            return;
-        }
-
-        if (isListening()) { // Should be always true.
-            mResult = result;
-            mLatch.countDown();
-        }
-    }
-
-    /**
-     * Listener method: notifies we are interested in the next action.
-     */
-    public void listen() {
-        if (isListening()) throw new RuntimeException("Should not happen.");
-        mResult = null;
-        mLatch = new CountDownLatch(1);
-    }
-
-    /**
-     * Listener method: waits for next task action to end.
-     * @param millis milliseconds
-     * @return the action result
-     */
-    public T await(long millis) {
-        return await(millis, TimeUnit.MILLISECONDS);
-    }
-
-    /**
-     * Listener method: waits 1 minute for next task action to end.
-     * @return the action result
-     */
-    public T await() {
-        return await(1, TimeUnit.MINUTES);
-    }
-
-    /**
-     * Listener method: waits for next task action to end.
-     * @param time time
-     * @param unit the time unit
-     * @return the action result
-     */
-    private T await(long time, @NonNull TimeUnit unit) {
-        try {
-            mLatch.await(time, unit);
-        } catch (Exception e) {
-            e.printStackTrace();
-        }
-        T result = mResult;
-        mResult = null;
-        mLatch = null;
-        return result;
-    }
-
-
-}

cameraview/src/main/java/com/otaliastudios/cameraview/preview/CameraPreview.java

@@ -18,7 +18,6 @@ import com.google.android.gms.tasks.TaskCompletionSource;
 import com.google.android.gms.tasks.Tasks;
 import com.otaliastudios.cameraview.CameraLogger;
 import com.otaliastudios.cameraview.engine.CameraEngine;
-import com.otaliastudios.cameraview.internal.utils.Op;
 import com.otaliastudios.cameraview.size.Size;
 
 /**
@@ -56,8 +55,11 @@ public abstract class CameraPreview<T extends View, Output> {
         void onSurfaceDestroyed();
     }
 
-    @VisibleForTesting
+    protected interface CropCallback {
-    Op<Void> mCropOp = new Op<>();
+        void onCrop();
+    }
+
+    @VisibleForTesting CropCallback mCropCallback;
     private SurfaceCallback mSurfaceCallback;
     private T mView;
     boolean mCropping;
@@ -152,7 +154,7 @@ public abstract class CameraPreview<T extends View, Output> {
         mInputStreamWidth = width;
         mInputStreamHeight = height;
         if (mInputStreamWidth > 0 && mInputStreamHeight > 0) {
-            crop(mCropOp);
+            crop(mCropCallback);
         }
     }
 
@@ -194,7 +196,7 @@ public abstract class CameraPreview<T extends View, Output> {
         mOutputSurfaceWidth = width;
         mOutputSurfaceHeight = height;
         if (mOutputSurfaceWidth > 0 && mOutputSurfaceHeight > 0) {
-            crop(mCropOp);
+            crop(mCropCallback);
         }
         if (mSurfaceCallback != null) {
             mSurfaceCallback.onSurfaceAvailable();
@@ -213,7 +215,7 @@ public abstract class CameraPreview<T extends View, Output> {
             mOutputSurfaceWidth = width;
             mOutputSurfaceHeight = height;
             if (width > 0 && height > 0) {
-                crop(mCropOp);
+                crop(mCropCallback);
             }
             if (mSurfaceCallback != null) {
                 mSurfaceCallback.onSurfaceChanged();
@@ -291,12 +293,11 @@ public abstract class CameraPreview<T extends View, Output> {
      * There might still be some absolute difference (e.g. same ratio but bigger / smaller).
      * However that should be already managed by the framework.
      *
-     * @param op the op
+     * @param callback the callback
      */
-    protected void crop(@NonNull Op<Void> op) {
+    protected void crop(@Nullable CropCallback callback) {
         // The base implementation does not support cropping.
-        op.start();
+        if (callback != null) callback.onCrop();
-        op.end(null);
     }
 
     /**

cameraview/src/main/java/com/otaliastudios/cameraview/preview/GlCameraPreview.java

@@ -5,6 +5,7 @@ import android.graphics.SurfaceTexture;
 import android.opengl.GLSurfaceView;
 import android.opengl.Matrix;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 
 import android.view.LayoutInflater;
@@ -14,7 +15,6 @@ import android.view.ViewGroup;
 
 import com.otaliastudios.cameraview.R;
 import com.otaliastudios.cameraview.internal.egl.EglViewport;
-import com.otaliastudios.cameraview.internal.utils.Op;
 import com.otaliastudios.cameraview.filter.Filter;
 import com.otaliastudios.cameraview.filter.NoFilter;
 import com.otaliastudios.cameraview.size.AspectRatio;
@@ -270,8 +270,7 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
      * See {@link Renderer#onDrawFrame(GL10)}.
      */
     @Override
-    protected void crop(@NonNull Op<Void> op) {
+    protected void crop(@Nullable final CropCallback callback) {
-        op.start();
         if (mInputStreamWidth > 0 && mInputStreamHeight > 0 && mOutputSurfaceWidth > 0
                 && mOutputSurfaceHeight > 0) {
             float scaleX = 1f, scaleY = 1f;
@@ -289,7 +288,7 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
             mCropScaleY = 1F / scaleY;
             getView().requestRender();
         }
-        op.end(null);
+        if (callback != null) callback.onCrop();
     }
 
     /**

cameraview/src/main/java/com/otaliastudios/cameraview/preview/TextureCameraPreview.java

@@ -17,7 +17,6 @@ import android.view.ViewGroup;
 import com.google.android.gms.tasks.TaskCompletionSource;
 import com.google.android.gms.tasks.Tasks;
 import com.otaliastudios.cameraview.R;
-import com.otaliastudios.cameraview.internal.utils.Op;
 import com.otaliastudios.cameraview.size.AspectRatio;
 
 import java.util.concurrent.ExecutionException;
@@ -91,14 +90,13 @@ public class TextureCameraPreview extends CameraPreview<TextureView, SurfaceText
     }
 
     @Override
-    protected void crop(final @NonNull Op<Void> op) {
+    protected void crop(@Nullable final CropCallback callback) {
-        op.start();
         getView().post(new Runnable() {
             @Override
             public void run() {
                 if (mInputStreamHeight == 0 || mInputStreamWidth == 0 ||
                         mOutputSurfaceHeight == 0 || mOutputSurfaceWidth == 0) {
-                    op.end(null);
+                    if (callback != null) callback.onCrop();
                     return;
                 }
                 float scaleX = 1f, scaleY = 1f;
@@ -118,7 +116,7 @@ public class TextureCameraPreview extends CameraPreview<TextureView, SurfaceText
                 mCropping = scaleX > 1.02f || scaleY > 1.02f;
                 LOG.i("crop:", "applied scaleX=", scaleX);
                 LOG.i("crop:", "applied scaleY=", scaleY);
-                op.end(null);
+                if (callback != null) callback.onCrop();
             }
         });
     }