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81 lines
2.4 KiB
81 lines
2.4 KiB
5 years ago
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---
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主线程为什么没有 ANR？
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---
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1. 了解 ANR 的触发的原理
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2. 了解应用大致启动流程
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3. 了解线程的消息循环机制
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4. 了解应用和系统服务通信过程
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#### ANR 是什么？
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```java
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final void appNotResponding(ProcessRecord app, ...){
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Message msg = Message.obtain();
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msg.what = SHOW_NOT_RESPONDING_MSG;
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mUiHandler.sendMessage(msg);
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}
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// SystemService 进程
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Dialog d = new AppNotRespondingDialog(...);
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d.show();
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```
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ANR 场景有哪些？
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1. Service Timeout
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2. BroadcastQueue Timeout
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3. ContentProvider Timeout
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4. InputDispatching Timeout
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以 Service 为例，看一下 ANR 是怎么触发的？
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```java
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void realStartServiceLocked(ServiceRecord r, ProcessRecord app, boolean execInfg){
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bumpServiceExecutingLocked(r, execInFg, "create");
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app.thread.scheduleCreateService(r, r.serviceInfo, ...);
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}
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void bumpServiceExecutingLocked(ServiceRecord r, boolean fg, String why){
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scheduleServiceTimeoutLocked(r.app);
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}
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void scheduleServiceTimeoutLocked(ProcessRecord proc){
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long now = SystemClock.uptimeMillis();
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Message msg = mAm.mHandler.obtainMessage(SERVICE_TIMEOUT_MSG);
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mAm.mHandler.sendMessageAtTime(msg, now+SERVICE_TIMEOUT);
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}
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void serviceTimeout(ProcessRecord proc){
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mAm.appNotResponding(proc, ...);
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}
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// 应用端处理 Service 请求
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private void handleCreateService(CreateServiceData data) {
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service = (Service)cl.loadClass(data.info.name).newInstance();
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ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
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Application app = packageInfo.makeApplication(false, mInstrumentation);
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service.attach(context, this, data.info.name, data.token, ...);
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service.onCreate();
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ActivityManagerNative.getDefault().serviceDoneExecuting(...);
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}
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private void serviceDoneExecutingLocked(ServiceRecord r, ...){
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mAm.mHandler.removeMessage(SERVICE_TIMEOUT_MSG, r.app);
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}
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```
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往主线程发消息：
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```java
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@Override
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void scheduleLaunchActivity(Intent intent, IBinder token, ...){
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sendMessage(H.LAUNCH_ACTIVITY, r);
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}
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void scheduleCreateService(IBinder token, ...){
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sendMessage(H.CREATE_SERVICE, s);
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}
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void scheduleReceiver(Intent intent, ActivityInfo info, ...){
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sendMessage(H.RECEIVER, r);
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}
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```
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#### 总结
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1. ANR 是应用没有在规定的时间内完成 AMS 指定的任务导致的
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2. AMS 请求调用应用端 binder 线程，再丢消息去唤醒主线程来处理
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3. ANR 不是因为主线程 loop 循环，而是因为主线程有耗时任务
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