Bug fixes (#651)

* Use CopyOnWriteArrayList for Camera2 action list. Fixes #649

* Listen to suspicious display rotation events. Fixes #623

* Correctly release GL objects on activity pause. Fixes #648

* Add synchronization in SnapshotVideoRecorder. Fixes #642

* Make Holder.getLastResult nullable. Fixes #621

* Fix tests

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

@@ -41,61 +41,68 @@ public class OrientationHelperTest extends BaseTest {
 
     @Test
     public void testEnable() {
-        assertNotNull(helper.mListener);
-        assertEquals(helper.getDisplayOffset(), -1);
-        assertEquals(helper.getDeviceOrientation(), -1);
+        // On some API levels, enable() needs to be run on the UI thread.
+        uiSync(new Runnable() {
+            @Override
+            public void run() {
+                assertEquals(helper.getLastDisplayOffset(), -1);
+                assertEquals(helper.getLastDeviceOrientation(), -1);
 
-        helper.enable(getContext());
-        assertNotNull(helper.mListener);
-        assertNotEquals(helper.getDisplayOffset(), -1); // Don't know about device orientation.
+                helper.enable();
+                assertNotEquals(helper.getLastDisplayOffset(), -1); // Don't know about device orientation.
 
                 // Ensure nothing bad if called twice.
-        helper.enable(getContext());
-        assertNotNull(helper.mListener);
-        assertNotEquals(helper.getDisplayOffset(), -1);
+                helper.enable();
+                assertNotEquals(helper.getLastDisplayOffset(), -1);
 
                 helper.disable();
-        assertNotNull(helper.mListener);
-        assertEquals(helper.getDisplayOffset(), -1);
-        assertEquals(helper.getDeviceOrientation(), -1);
+                assertEquals(helper.getLastDisplayOffset(), -1);
+                assertEquals(helper.getLastDeviceOrientation(), -1);
+            }
+        });
     }
 
     @Test
     public void testRotation() {
-
+        // On some API levels, enable() needs to be run on the UI thread.
+        uiSync(new Runnable() {
+            @Override
+            public void run() {
                 // Sometimes (on some APIs) the helper will trigger an update to 0
                 // right after enabling. But that's fine for us, times(1) will be OK either way.
-        helper.enable(getContext());
-        helper.mListener.onOrientationChanged(OrientationEventListener.ORIENTATION_UNKNOWN);
-        assertEquals(helper.getDeviceOrientation(), 0);
-        helper.mListener.onOrientationChanged(10);
-        assertEquals(helper.getDeviceOrientation(), 0);
-        helper.mListener.onOrientationChanged(-10);
-        assertEquals(helper.getDeviceOrientation(), 0);
-        helper.mListener.onOrientationChanged(44);
-        assertEquals(helper.getDeviceOrientation(), 0);
-        helper.mListener.onOrientationChanged(360);
-        assertEquals(helper.getDeviceOrientation(), 0);
+                helper.enable();
+                helper.mDeviceOrientationListener.onOrientationChanged(OrientationEventListener.ORIENTATION_UNKNOWN);
+                assertEquals(helper.getLastDeviceOrientation(), 0);
+                helper.mDeviceOrientationListener.onOrientationChanged(10);
+                assertEquals(helper.getLastDeviceOrientation(), 0);
+                helper.mDeviceOrientationListener.onOrientationChanged(-10);
+                assertEquals(helper.getLastDeviceOrientation(), 0);
+                helper.mDeviceOrientationListener.onOrientationChanged(44);
+                assertEquals(helper.getLastDeviceOrientation(), 0);
+                helper.mDeviceOrientationListener.onOrientationChanged(360);
+                assertEquals(helper.getLastDeviceOrientation(), 0);
 
                 // Callback called just once.
                 verify(callback, times(1)).onDeviceOrientationChanged(0);
 
-        helper.mListener.onOrientationChanged(90);
-        helper.mListener.onOrientationChanged(91);
-        assertEquals(helper.getDeviceOrientation(), 90);
+                helper.mDeviceOrientationListener.onOrientationChanged(90);
+                helper.mDeviceOrientationListener.onOrientationChanged(91);
+                assertEquals(helper.getLastDeviceOrientation(), 90);
                 verify(callback, times(1)).onDeviceOrientationChanged(90);
 
-        helper.mListener.onOrientationChanged(180);
-        assertEquals(helper.getDeviceOrientation(), 180);
+                helper.mDeviceOrientationListener.onOrientationChanged(180);
+                assertEquals(helper.getLastDeviceOrientation(), 180);
                 verify(callback, times(1)).onDeviceOrientationChanged(180);
 
-        helper.mListener.onOrientationChanged(270);
-        assertEquals(helper.getDeviceOrientation(), 270);
+                helper.mDeviceOrientationListener.onOrientationChanged(270);
+                assertEquals(helper.getLastDeviceOrientation(), 270);
                 verify(callback, times(1)).onDeviceOrientationChanged(270);
 
                 // It is still 270 after ORIENTATION_UNKNOWN
-        helper.mListener.onOrientationChanged(OrientationEventListener.ORIENTATION_UNKNOWN);
-        assertEquals(helper.getDeviceOrientation(), 270);
+                helper.mDeviceOrientationListener.onOrientationChanged(OrientationEventListener.ORIENTATION_UNKNOWN);
+                assertEquals(helper.getLastDeviceOrientation(), 270);
                 verify(callback, times(1)).onDeviceOrientationChanged(270);
             }
+        });
+    }
 }

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

@@ -356,7 +356,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
             // attached. That's why we instantiate the preview here.
             doInstantiatePreview();
         }
-        mOrientationHelper.enable(getContext());
+        mOrientationHelper.enable();
     }
 
     @Override
@@ -722,8 +722,8 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         if (mCameraPreview != null) mCameraPreview.onResume();
         if (checkPermissions(getAudio())) {
             // Update display orientation for current CameraEngine
-            mOrientationHelper.enable(getContext());
-            mCameraEngine.getAngles().setDisplayOffset(mOrientationHelper.getDisplayOffset());
+            mOrientationHelper.enable();
+            mCameraEngine.getAngles().setDisplayOffset(mOrientationHelper.getLastDisplayOffset());
             mCameraEngine.start();
         }
     }
@@ -2073,7 +2073,7 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         @Override
         public void onDeviceOrientationChanged(int deviceOrientation) {
             mLogger.i("onDeviceOrientationChanged", deviceOrientation);
-            int displayOffset = mOrientationHelper.getDisplayOffset();
+            int displayOffset = mOrientationHelper.getLastDisplayOffset();
             if (!mUseDeviceOrientation) {
                 // To fool the engine to return outputs in the VIEW reference system,
                 // The device orientation should be set to -displayOffset.
@@ -2093,6 +2093,19 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
             });
         }
 
+        @Override
+        public void onDisplayOffsetChanged(int displayOffset, boolean willRecreate) {
+            mLogger.i("onDisplayOffsetChanged", displayOffset, "recreate:", willRecreate);
+            if (isOpened() && !willRecreate) {
+                // Display offset changes when the device rotation lock is off and the activity
+                // is free to rotate. However, some changes will NOT recreate the activity, namely
+                // 180 degrees flips. In this case, we must restart the camera manually.
+                mLogger.w("onDisplayOffsetChanged", "restarting the camera.");
+                close();
+                open();
+            }
+        }
+
         @Override
         public void dispatchOnZoomChanged(final float newValue, @Nullable final PointF[] fingers) {
             mLogger.i("dispatchOnZoomChanged", newValue);

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

@@ -70,6 +70,7 @@ import com.otaliastudios.cameraview.video.SnapshotVideoRecorder;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.ExecutionException;
 
 @RequiresApi(Build.VERSION_CODES.LOLLIPOP)
@@ -111,7 +112,8 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
     private final boolean mPictureCaptureStopsPreview = false; // can be configurable at some point
 
     // Actions
-    private final List<Action> mActions = new ArrayList<>();
+    // Use COW to properly synchronize the list. We'll iterate much more than mutate
+    private final List<Action> mActions = new CopyOnWriteArrayList<>();
     private MeterAction mMeterAction;
 
     public Camera2Engine(Callback callback) {
@@ -1428,29 +1430,15 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
 
     @Override
     public void addAction(final @NonNull Action action) {
-        // This is likely to be called during a Capture callback while we iterate
-        // on the actions list, or worse, from other threads. We must use mHandler.post.
-        mHandler.post(new Runnable() {
-            @Override
-            public void run() {
         if (!mActions.contains(action)) {
             mActions.add(action);
         }
     }
-        });
-    }
 
     @Override
     public void removeAction(final @NonNull Action action) {
-        // This is likely to be called during a Capture callback while we iterate
-        // on the actions list, or worse, from other threads. We must use mHandler.post.
-        mHandler.post(new Runnable() {
-            @Override
-            public void run() {
         mActions.remove(action);
     }
-        });
-    }
 
     @NonNull
     @Override
@@ -1458,7 +1446,7 @@ public class Camera2Engine extends CameraEngine implements ImageReader.OnImageAv
         return mCameraCharacteristics;
     }
 
-    @NonNull
+    @Nullable
     @Override
     public TotalCaptureResult getLastResult(@NonNull Action action) {
         return mLastRepeatingResult;

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

@@ -36,7 +36,7 @@ class LogAction extends BaseAction {
                 " afState: " + afState + " afTriggerState: " + afTriggerState;
         if (!log.equals(lastLog)) {
             lastLog = log;
-            LOG.i(log);
+            LOG.v(log);
         }
     }
 

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

@@ -8,6 +8,7 @@ import android.hardware.camera2.TotalCaptureResult;
 import android.os.Build;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
 
 /**
@@ -51,7 +52,7 @@ public interface ActionHolder {
      * @param action action
      * @return last result
      */
-    @NonNull
+    @Nullable
     TotalCaptureResult getLastResult(@NonNull Action action);
 
     /**

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/ExposureLock.java

@@ -40,10 +40,16 @@ public class ExposureLock extends BaseLock {
 
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
-        Integer aeState = holder.getLastResult(this).get(CaptureResult.CONTROL_AE_STATE);
+        CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
+            Integer aeState = lastResult.get(CaptureResult.CONTROL_AE_STATE);
             boolean result = aeState != null && aeState == CaptureResult.CONTROL_AE_STATE_LOCKED;
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/FocusLock.java

@@ -35,6 +35,7 @@ public class FocusLock extends BaseLock {
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
         CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
             Integer afState = lastResult.get(CaptureResult.CONTROL_AF_STATE);
             boolean afStateOk = afState != null &&
                     (afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED
@@ -47,6 +48,10 @@ public class FocusLock extends BaseLock {
             boolean result = afStateOk && afModeOk;
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/lock/WhiteBalanceLock.java

@@ -33,10 +33,17 @@ public class WhiteBalanceLock extends BaseLock {
 
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
-        Integer awbState = holder.getLastResult(this).get(CaptureResult.CONTROL_AWB_STATE);
-        boolean result = awbState != null && awbState == CaptureRequest.CONTROL_AWB_STATE_LOCKED;
+        CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
+            Integer awbState = lastResult.get(CaptureResult.CONTROL_AWB_STATE);
+            boolean result = awbState != null
+                    && awbState == CaptureRequest.CONTROL_AWB_STATE_LOCKED;
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/ExposureMeter.java

@@ -50,10 +50,16 @@ public class ExposureMeter extends BaseMeter {
 
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
-        Integer aeState = holder.getLastResult(this).get(CaptureResult.CONTROL_AE_STATE);
+        CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
+            Integer aeState = lastResult.get(CaptureResult.CONTROL_AE_STATE);
             boolean result = aeState != null && aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED;
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/ExposureReset.java

@@ -37,8 +37,9 @@ public class ExposureReset extends BaseReset {
         }
 
         // NOTE: precapture might not be supported, in which case I think it will be ignored.
-        Integer trigger = holder.getLastResult(this)
-                .get(CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER);
+        CaptureResult lastResult = holder.getLastResult(this);
+        Integer trigger = lastResult == null ? null
+                : lastResult.get(CaptureResult.CONTROL_AE_PRECAPTURE_TRIGGER);
         LOG.i("onStarted:", "last precapture trigger is", trigger);
         if (trigger != null && trigger == CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START) {
             LOG.i("onStarted:", "canceling precapture.");

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/FocusMeter.java

@@ -40,12 +40,18 @@ public class FocusMeter extends BaseMeter {
 
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
-        Integer afState = holder.getLastResult(this).get(CaptureResult.CONTROL_AF_STATE);
+        CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
+            Integer afState = lastResult.get(CaptureResult.CONTROL_AF_STATE);
             boolean result = afState != null &&
                     (afState == CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED ||
                             afState == CaptureResult.CONTROL_AF_STATE_PASSIVE_FOCUSED);
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/FocusReset.java

@@ -36,7 +36,9 @@ public class FocusReset extends BaseReset {
         }
 
         // NOTE: trigger might not be supported, in which case I think it will be ignored.
-        Integer trigger = holder.getLastResult(this).get(CaptureResult.CONTROL_AF_TRIGGER);
+        CaptureResult lastResult = holder.getLastResult(this);
+        Integer trigger = lastResult == null ? null
+                : lastResult.get(CaptureResult.CONTROL_AF_TRIGGER);
         LOG.w("onStarted:", "last focus trigger is", trigger);
         if (trigger != null && trigger == CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START) {
             holder.getBuilder(this).set(CaptureRequest.CONTROL_AF_TRIGGER,

cameraview/src/main/java/com/otaliastudios/cameraview/engine/meter/WhiteBalanceMeter.java

@@ -40,10 +40,17 @@ public class WhiteBalanceMeter extends BaseMeter {
 
     @Override
     protected boolean checkShouldSkip(@NonNull ActionHolder holder) {
-        Integer awbState = holder.getLastResult(this).get(CaptureResult.CONTROL_AWB_STATE);
-        boolean result = awbState != null && awbState == CaptureRequest.CONTROL_AWB_STATE_CONVERGED;
+        CaptureResult lastResult = holder.getLastResult(this);
+        if (lastResult != null) {
+            Integer awbState = lastResult.get(CaptureResult.CONTROL_AWB_STATE);
+            boolean result = awbState != null
+                    && awbState == CaptureRequest.CONTROL_AWB_STATE_CONVERGED;
             LOG.i("checkShouldSkip:", result);
             return result;
+        } else {
+            LOG.i("checkShouldSkip: false - lastResult is null.");
+            return false;
+        }
     }
 
     @Override

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

@@ -5,6 +5,8 @@ import android.hardware.SensorManager;
 import androidx.annotation.NonNull;
 import androidx.annotation.VisibleForTesting;
 
+import android.hardware.display.DisplayManager;
+import android.os.Build;
 import android.view.Display;
 import android.view.OrientationEventListener;
 import android.view.Surface;
@@ -12,21 +14,28 @@ import android.view.WindowManager;
 
 /**
  * Helps with keeping track of both device orientation (which changes when device is rotated)
- * and the display offset (which depends on the activity orientation
- * wrt the device default orientation).
+ * and the display offset (which depends on the activity orientation wrt the device default
+ * orientation).
  */
 public class OrientationHelper {
 
     /**
-     * Receives callback about the device orientation changes.
+     * Receives callback about the orientation changes.
      */
     public interface Callback {
         void onDeviceOrientationChanged(int deviceOrientation);
+        void onDisplayOffsetChanged(int displayOffset, boolean willRecreate);
     }
 
-    @VisibleForTesting final OrientationEventListener mListener;
+    private final Context mContext;
     private final Callback mCallback;
+
+    @VisibleForTesting
+    final OrientationEventListener mDeviceOrientationListener;
     private int mDeviceOrientation = -1;
+
+    @VisibleForTesting
+    final DisplayManager.DisplayListener mDisplayOffsetListener;
     private int mDisplayOffset = -1;
 
     /**
@@ -35,57 +44,78 @@ public class OrientationHelper {
      * @param callback a {@link Callback}
      */
     public OrientationHelper(@NonNull Context context, @NonNull Callback callback) {
+        mContext = context;
         mCallback = callback;
-        mListener = new OrientationEventListener(context.getApplicationContext(),
+        mDeviceOrientationListener = new OrientationEventListener(context.getApplicationContext(),
                 SensorManager.SENSOR_DELAY_NORMAL) {
 
             @SuppressWarnings("ConstantConditions")
             @Override
             public void onOrientationChanged(int orientation) {
-                int or = 0;
+                int deviceOrientation = 0;
                 if (orientation == OrientationEventListener.ORIENTATION_UNKNOWN) {
-                    or = mDeviceOrientation != -1 ? mDeviceOrientation : 0;
+                    deviceOrientation = mDeviceOrientation != -1 ? mDeviceOrientation : 0;
                 } else if (orientation >= 315 || orientation < 45) {
-                    or = 0;
+                    deviceOrientation = 0;
                 } else if (orientation >= 45 && orientation < 135) {
-                    or = 90;
+                    deviceOrientation = 90;
                 } else if (orientation >= 135 && orientation < 225) {
-                    or = 180;
+                    deviceOrientation = 180;
                 } else if (orientation >= 225 && orientation < 315) {
-                    or = 270;
+                    deviceOrientation = 270;
                 }
 
-                if (or != mDeviceOrientation) {
-                    mDeviceOrientation = or;
+                if (deviceOrientation != mDeviceOrientation) {
+                    mDeviceOrientation = deviceOrientation;
                     mCallback.onDeviceOrientationChanged(mDeviceOrientation);
                 }
             }
         };
+        if (Build.VERSION.SDK_INT >= 17) {
+            mDisplayOffsetListener = new DisplayManager.DisplayListener() {
+                public void onDisplayAdded(int displayId) { }
+                public void onDisplayRemoved(int displayId) { }
+
+                @Override
+                public void onDisplayChanged(int displayId) {
+                    int oldDisplayOffset = mDisplayOffset;
+                    int newDisplayOffset = findDisplayOffset();
+                    if (newDisplayOffset != oldDisplayOffset) {
+                        mDisplayOffset = newDisplayOffset;
+                        // With 180 degrees flips, the activity is not recreated.
+                        boolean willRecreate = Math.abs(newDisplayOffset - oldDisplayOffset) != 180;
+                        mCallback.onDisplayOffsetChanged(newDisplayOffset, willRecreate);
+                    }
+                }
+            };
+        } else {
+            mDisplayOffsetListener = null;
+        }
     }
 
     /**
      * Enables this listener.
-     * @param context a context
      */
-    public void enable(@NonNull Context context) {
-        Display display = ((WindowManager) context
-                .getSystemService(Context.WINDOW_SERVICE))
-                .getDefaultDisplay();
-        switch (display.getRotation()) {
-            case Surface.ROTATION_0: mDisplayOffset = 0; break;
-            case Surface.ROTATION_90: mDisplayOffset = 90; break;
-            case Surface.ROTATION_180: mDisplayOffset = 180; break;
-            case Surface.ROTATION_270: mDisplayOffset = 270; break;
-            default: mDisplayOffset = 0; break;
+    public void enable() {
+        mDisplayOffset = findDisplayOffset();
+        if (Build.VERSION.SDK_INT >= 17) {
+            DisplayManager manager = (DisplayManager)
+                    mContext.getSystemService(Context.DISPLAY_SERVICE);
+            manager.registerDisplayListener(mDisplayOffsetListener, null);
         }
-        mListener.enable();
+        mDeviceOrientationListener.enable();
     }
 
     /**
      * Disables this listener.
      */
     public void disable() {
-        mListener.disable();
+        mDeviceOrientationListener.disable();
+        if (Build.VERSION.SDK_INT >= 17) {
+            DisplayManager manager = (DisplayManager)
+                    mContext.getSystemService(Context.DISPLAY_SERVICE);
+            manager.unregisterDisplayListener(mDisplayOffsetListener);
+        }
         mDisplayOffset = -1;
         mDeviceOrientation = -1;
     }
@@ -94,7 +124,8 @@ public class OrientationHelper {
      * Returns the current device orientation.
      * @return device orientation
      */
-    public int getDeviceOrientation() {
+    @SuppressWarnings("WeakerAccess")
+    public int getLastDeviceOrientation() {
         return mDeviceOrientation;
     }
 
@@ -102,7 +133,20 @@ public class OrientationHelper {
      * Returns the current display offset.
      * @return display offset
      */
-    public int getDisplayOffset() {
+    public int getLastDisplayOffset() {
         return mDisplayOffset;
     }
+
+    private int findDisplayOffset() {
+        Display display = ((WindowManager) mContext
+                .getSystemService(Context.WINDOW_SERVICE))
+                .getDefaultDisplay();
+        switch (display.getRotation()) {
+            case Surface.ROTATION_0: return 0;
+            case Surface.ROTATION_90: return 90;
+            case Surface.ROTATION_180: return 180;
+            case Surface.ROTATION_270: return 270;
+            default: return 0;
+        }
+    }
 }

cameraview/src/main/java/com/otaliastudios/cameraview/picture/Snapshot2PictureRecorder.java

@@ -106,7 +106,13 @@ public class Snapshot2PictureRecorder extends SnapshotGlPictureRecorder {
             }
         });
 
-        Integer aeState = mHolder.getLastResult(mAction).get(CaptureResult.CONTROL_AE_STATE);
+        CaptureResult lastResult = mHolder.getLastResult(mAction);
+        if (lastResult == null) {
+            LOG.w("Picture snapshot requested very early, before the first preview frame.",
+                    "Metering might not work as intended.");
+        }
+        Integer aeState = lastResult == null ? null
+                : lastResult.get(CaptureResult.CONTROL_AE_STATE);
         mActionNeeded = engine.getPictureSnapshotMetering()
                 && aeState != null
                 && aeState == CaptureResult.CONTROL_AE_STATE_FLASH_REQUIRED;

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

@@ -2,7 +2,6 @@ package com.otaliastudios.cameraview.preview;
 
 import android.content.Context;
 import android.graphics.SurfaceTexture;
-import android.hardware.camera2.CaptureResult;
 import android.opengl.GLSurfaceView;
 import android.opengl.Matrix;
 import androidx.annotation.NonNull;
@@ -20,8 +19,6 @@ import com.otaliastudios.cameraview.filter.Filter;
 import com.otaliastudios.cameraview.filter.NoFilter;
 import com.otaliastudios.cameraview.size.AspectRatio;
 
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.Set;
 import java.util.concurrent.CopyOnWriteArraySet;
 
@@ -87,9 +84,10 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
     protected GLSurfaceView onCreateView(@NonNull Context context, @NonNull ViewGroup parent) {
         ViewGroup root = (ViewGroup) LayoutInflater.from(context)
                 .inflate(R.layout.cameraview_gl_view, parent, false);
-        GLSurfaceView glView = root.findViewById(R.id.gl_surface_view);
+        final GLSurfaceView glView = root.findViewById(R.id.gl_surface_view);
+        final Renderer renderer = instantiateRenderer();
         glView.setEGLContextClientVersion(2);
-        glView.setRenderer(instantiateRenderer());
+        glView.setRenderer(renderer);
         glView.setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
         glView.getHolder().addCallback(new SurfaceHolder.Callback() {
             public void surfaceCreated(SurfaceHolder holder) {}
@@ -97,6 +95,12 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
 
             @Override
             public void surfaceDestroyed(SurfaceHolder holder) {
+                glView.queueEvent(new Runnable() {
+                    @Override
+                    public void run() {
+                        renderer.onSurfaceDestroyed();
+                    }
+                });
                 dispatchOnSurfaceDestroyed();
                 mDispatched = false;
             }
@@ -129,16 +133,6 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
         super.onDestroy();
         // View is gone, so EGL context is gone: callbacks make no sense anymore.
         mRendererFrameCallbacks.clear();
-        if (mInputSurfaceTexture != null) {
-            mInputSurfaceTexture.setOnFrameAvailableListener(null);
-            mInputSurfaceTexture.release();
-            mInputSurfaceTexture = null;
-        }
-        mOutputTextureId = 0;
-        if (mOutputViewport != null) {
-            mOutputViewport.release();
-            mOutputViewport = null;
-        }
     }
 
     /**
@@ -174,6 +168,21 @@ public class GlCameraPreview extends FilterCameraPreview<GLSurfaceView, SurfaceT
             });
         }
 
+        @SuppressWarnings("WeakerAccess")
+        @RendererThread
+        public void onSurfaceDestroyed() {
+            if (mInputSurfaceTexture != null) {
+                mInputSurfaceTexture.setOnFrameAvailableListener(null);
+                mInputSurfaceTexture.release();
+                mInputSurfaceTexture = null;
+            }
+            mOutputTextureId = 0;
+            if (mOutputViewport != null) {
+                mOutputViewport.release();
+                mOutputViewport = null;
+            }
+        }
+
         @RendererThread
         @Override
         public void onSurfaceChanged(GL10 gl, final int width, final int height) {

cameraview/src/main/java/com/otaliastudios/cameraview/video/SnapshotVideoRecorder.java

@@ -51,6 +51,7 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
     private static final int STATE_NOT_RECORDING = 1;
 
     private MediaEncoderEngine mEncoderEngine;
+    private final Object mEncoderEngineLock = new Object();
     private GlCameraPreview mPreview;
 
     private int mCurrentState = STATE_NOT_RECORDING;
@@ -82,14 +83,21 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
         dispatchVideoRecordingStart();
     }
 
+    // Can be called different threads
     @Override
     protected void onStop(boolean isCameraShutdown) {
         if (isCameraShutdown) {
-            // The renderer callback might never be called. From my tests, it's not.
+            // The renderer callback might never be called. From my tests, it's not,
+            // so we can't wait for that callback to stop the encoder engine.
             LOG.i("Stopping the encoder engine from isCameraShutdown.");
             mDesiredState = STATE_NOT_RECORDING;
             mCurrentState = STATE_NOT_RECORDING;
+            synchronized (mEncoderEngineLock) {
+                if (mEncoderEngine != null) {
                     mEncoderEngine.stop();
+                    mEncoderEngine = null;
+                }
+            }
         } else {
             mDesiredState = STATE_NOT_RECORDING;
         }
@@ -104,14 +112,17 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
         }
     }
 
+    @RendererThread
     @Override
     public void onRendererFilterChanged(@NonNull Filter filter) {
         mCurrentFilter = filter.copy();
-        if (mEncoderEngine != null) {
         mCurrentFilter.setSize(mResult.size.getWidth(), mResult.size.getHeight());
+        synchronized (mEncoderEngineLock) {
+            if (mEncoderEngine != null) {
                 mEncoderEngine.notify(TextureMediaEncoder.FILTER_EVENT, mCurrentFilter);
             }
         }
+    }
 
     @RendererThread
     @Override
@@ -206,6 +217,7 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
             }
 
             // Engine
+            synchronized (mEncoderEngineLock) {
                 mEncoderEngine = new MediaEncoderEngine(mResult.file,
                         videoEncoder,
                         audioEncoder,
@@ -214,6 +226,7 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
                         SnapshotVideoRecorder.this);
                 mEncoderEngine.notify(TextureMediaEncoder.FILTER_EVENT, mCurrentFilter);
                 mEncoderEngine.start();
+            }
             mCurrentState = STATE_RECORDING;
         }
 
@@ -226,15 +239,22 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
             // NOTE: this is an approximation but it seems to work:
             frame.timestampMillis = System.currentTimeMillis();
             surfaceTexture.getTransformMatrix(frame.transform);
-            if (mEncoderEngine != null) { // Can happen on teardown. At least it used to.
+            synchronized (mEncoderEngineLock) {
+                if (mEncoderEngine != null) { // Can be null on teardown.
                     mEncoderEngine.notify(TextureMediaEncoder.FRAME_EVENT, frame);
                 }
             }
+        }
 
         if (mCurrentState == STATE_RECORDING && mDesiredState == STATE_NOT_RECORDING) {
             LOG.i("Stopping the encoder engine.");
             mCurrentState = STATE_NOT_RECORDING;
+            synchronized (mEncoderEngineLock) {
+                if (mEncoderEngine != null) {
                     mEncoderEngine.stop();
+                    mEncoderEngine = null;
+                }
+            }
         }
 
     }
@@ -280,7 +300,9 @@ public class SnapshotVideoRecorder extends VideoRecorder implements RendererFram
             mOverlayDrawer.release();
             mOverlayDrawer = null;
         }
+        synchronized (mEncoderEngineLock) {
             mEncoderEngine = null;
+        }
         dispatchResult();
     }
 }

cameraview/src/main/java/com/otaliastudios/cameraview/video/VideoRecorder.java

@@ -50,6 +50,7 @@ public abstract class VideoRecorder {
     @SuppressWarnings("WeakerAccess")
     protected Exception mError;
     private int mState;
+    private final Object mStateLock = new Object();
 
     /**
      * Creates a new video recorder.
@@ -66,12 +67,14 @@ public abstract class VideoRecorder {
      * @param stub the video stub
      */
     public final void start(@NonNull VideoResult.Stub stub) {
+        synchronized (mStateLock) {
             if (mState != STATE_IDLE) {
                 LOG.e("start:", "called twice, or while stopping! " +
                         "Ignoring. state:", mState);
                 return;
             }
             mState = STATE_RECORDING;
+        }
         mResult = stub;
         onStart();
     }
@@ -81,12 +84,15 @@ public abstract class VideoRecorder {
      * @param isCameraShutdown whether this is a full shutdown, camera is being closed
      */
     public final void stop(boolean isCameraShutdown) {
+        synchronized (mStateLock) {
             if (mState == STATE_IDLE) {
+                // Do not check for STOPPING! See onStop().
                 LOG.e("stop:", "called twice, or called before start! " +
                         "Ignoring. isCameraShutdown:", isCameraShutdown);
                 return;
             }
             mState = STATE_STOPPING;
+        }
         onStop(isCameraShutdown);
     }
 
@@ -96,11 +102,19 @@ public abstract class VideoRecorder {
      */
     public boolean isRecording() {
         // true if not idle.
+        synchronized (mStateLock) {
             return mState != STATE_IDLE;
         }
+    }
 
     protected abstract void onStart();
 
+    /**
+     * Should stop recording as fast as possible. This can be called twice because the
+     * shutdown boolean might be different.
+     *
+     * @param isCameraShutdown whether camera is shutting down
+     */
     protected abstract void onStop(boolean isCameraShutdown);
 
     /**
@@ -108,8 +122,10 @@ public abstract class VideoRecorder {
      * either with some error (null result) or with the actual stub, filled.
      */
     protected final void dispatchResult() {
+        synchronized (mStateLock) {
             if (!isRecording()) return;
             mState = STATE_IDLE;
+        }
         onDispatchResult();
         if (mListener != null) {
             mListener.onVideoResult(mResult, mError);

demo/src/main/java/com/otaliastudios/cameraview/demo/CameraActivity.java

@@ -351,9 +351,11 @@ public class CameraActivity extends AppCompatActivity implements View.OnClickLis
             mCurrentFilter = 0;
         }
         Filters filter = mAllFilters[mCurrentFilter];
-        camera.setFilter(filter.newInstance());
         message(filter.toString(), false);
 
+        // Normal behavior:
+        camera.setFilter(filter.newInstance());
+
         // To test MultiFilter:
         // DuotoneFilter duotone = new DuotoneFilter();
         // duotone.setFirstColor(Color.RED);