本文主要是介绍Android ANR原理分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
一、概述
ANR(Application Not responding)，是指应用程序未响应，Android系统对于一些事件需要在一定的时间范围内完成，如果超过预定时间能未能得到有效响应或者响应时间过长，都会造成ANR。一般地，这时往往会弹出一个提示框，告知用户当前xxx未响应，用户可选择继续等待或者Force Close。
那么哪些场景会造成ANR呢？
- Service Timeout:服务在20s内未执行完成；
- BroadcastQueue Timeout：比如前台广播在10s内执行完成
- ContentProvider Timeout：内容提供者执行超时
- inputDispatching Timeout: 输入事件分发超时5s，包括按键分发事件的超时。
二、ANR触发时机
2.1 Service Timeout
Service Timeout触发时机，简单说就是AMS中的mHandler收到SERVICE_TIMEOUT_MSG消息时触发。
在前面文章startService流程分析详细介绍Service启动流程，在Service所在进程attach到system_server进程的过程中会调用realStartServiceLocked()方法
2.1.1 realStartServiceLocked
[-> ActiveServices.java]
private final void realStartServiceLocked(ServiceRecord r,ProcessRecord app, boolean execInFg) throws RemoteException {...//发送delay消息(SERVICE_TIMEOUT_MSG)，【见小节2.1.2】bumpServiceExecutingLocked(r, execInFg, "create");try {...//最终执行服务的onCreate()方法app.thread.scheduleCreateService(r, r.serviceInfo,mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),app.repProcState);} catch (DeadObjectException e) {...} finally {if (!created) {//当service启动完毕，则remove SERVICE_TIMEOUT_MSG消息【见小节2.1.3】serviceDoneExecutingLocked(r, inDestroying, inDestroying);...}}
}
2.1.2 bumpServiceExecutingLocked
该方法的主要工作发送delay消息(SERVICE_TIMEOUT_MSG)
private final void bumpServiceExecutingLocked(ServiceRecord r, boolean fg, String why) {...scheduleServiceTimeoutLocked(r.app);
}
void scheduleServiceTimeoutLocked(ProcessRecord proc) {if (proc.executingServices.size() == 0 || proc.thread == null) {return;}long now = SystemClock.uptimeMillis();Message msg = mAm.mHandler.obtainMessage(ActivityManagerService.SERVICE_TIMEOUT_MSG);msg.obj = proc;//当超时后仍没有remove该SERVICE_TIMEOUT_MSG消息，则执行service Timeout流程【见2.1.4】mAm.mHandler.sendMessageAtTime(msg,proc.execServicesFg ? (now+SERVICE_TIMEOUT) : (now+ SERVICE_BACKGROUND_TIMEOUT));
}
- 对于前台服务，则超时为
SERVICE_TIMEOUT，即timeout=20s； - 对于后台服务，则超时为
SERVICE_BACKGROUND_TIMEOUT，即timeout=200s；
2.1.3 serviceDoneExecutingLocked
该方法的主要工作是当service启动完成，则移除service Timeout消息。
private void serviceDoneExecutingLocked(ServiceRecord r, boolean inDestroying,boolean finishing) {...if (r.executeNesting <= 0) {if (r.app != null) {r.app.execServicesFg = false;r.app.executingServices.remove(r);if (r.app.executingServices.size() == 0) {//当前服务所在进程中没有正在执行的servicemAm.mHandler.removeMessages(ActivityManagerService.SERVICE_TIMEOUT_MSG, r.app);...}...
}
2.1.4 SERVICE_TIMEOUT_MSG
到此不难理解，当SERVICE_TIMEOUT_MSG消息成功发送时，则AMS中的mHandler收到该消息则触发调用serviceTimeout。
final class MainHandler extends Handler {public void handleMessage(Message msg) {switch (msg.what) {case SERVICE_TIMEOUT_MSG: {...//【见小节2.1.5】mServices.serviceTimeout((ProcessRecord)msg.obj);} break;...}...}
}
2.1.5 serviceTimeout
[-> ActiveServices.java]
void serviceTimeout(ProcessRecord proc) {String anrMessage = null;synchronized(mAm) {if (proc.executingServices.size() == 0 || proc.thread == null) {return;}final long now = SystemClock.uptimeMillis();final long maxTime = now -(proc.execServicesFg ? SERVICE_TIMEOUT : SERVICE_BACKGROUND_TIMEOUT);ServiceRecord timeout = null;long nextTime = 0;for (int i=proc.executingServices.size()-1; i>=0; i--) {ServiceRecord sr = proc.executingServices.valueAt(i);if (sr.executingStart < maxTime) {timeout = sr;break;}if (sr.executingStart > nextTime) {nextTime = sr.executingStart;}}if (timeout != null && mAm.mLruProcesses.contains(proc)) {Slog.w(TAG, "Timeout executing service: " + timeout);StringWriter sw = new StringWriter();PrintWriter pw = new FastPrintWriter(sw, false, 1024);pw.println(timeout);timeout.dump(pw, " ");pw.close();mLastAnrDump = sw.toString();mAm.mHandler.removeCallbacks(mLastAnrDumpClearer);mAm.mHandler.postDelayed(mLastAnrDumpClearer, LAST_ANR_LIFETIME_DURATION_MSECS);anrMessage = "executing service " + timeout.shortName;}}if (anrMessage != null) {//当存在timeout的service，则执行appNotResponding【见小节3.1】mAm.appNotResponding(proc, null, null, false, anrMessage);}
}
其中anrMessage的内容为”executing service [发送超时serviceRecord信息]”;
2.2 BroadcastQueue Timeout
BroadcastQueue Timeout触发时机，简单说就是BroadcastQueue中的mHandler收到BROADCAST_TIMEOUT_MSG消息时触发。
在前面文章Android Broadcast广播机制分析详细介绍广播启动流程，在发送广播过程中会执行scheduleBroadcastsLocked方法来处理相关的广播，然后会调用到processNextBroadcast方法来处理下一条广播。
processNextBroadcast执行过程分4步骤：
- step1. 处理并行广播
- step2. 处理当前有序广播
- step3. 获取下条有序广播
- step4. 处理下条有序广播
2.2.1 processNextBroadcast
[-> BroadcastQueue.java]
final void processNextBroadcast(boolean fromMsg) {synchronized(mService) {...//step 2: 处理当前有序广播do {r = mOrderedBroadcasts.get(0);//获取所有该广播所有的接收者int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;if (mService.mProcessesReady && r.dispatchTime > 0) {long now = SystemClock.uptimeMillis();if ((numReceivers > 0) &&(now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {//当广播处理时间超时，则强制结束这条广播【见小节2.2.5】broadcastTimeoutLocked(false);...}}if (r.receivers == null || r.nextReceiver >= numReceivers|| r.resultAbort || forceReceive) {if (r.resultTo != null) {//处理广播消息消息performReceiveLocked(r.callerApp, r.resultTo,new Intent(r.intent), r.resultCode,r.resultData, r.resultExtras, false, false, r.userId);r.resultTo = null;}//取消BROADCAST_TIMEOUT_MSG消息【见小节2.2.3】cancelBroadcastTimeoutLocked();}} while (r == null);...//step 3: 获取下条有序广播r.receiverTime = SystemClock.uptimeMillis();if (!mPendingBroadcastTimeoutMessage) {long timeoutTime = r.receiverTime + mTimeoutPeriod;//设置广播超时时间，发送BROADCAST_TIMEOUT_MSG【见小节2.2.2】setBroadcastTimeoutLocked(timeoutTime);}...}
}
对于广播超时处理时机：
- 首先在step3的过程中setBroadcastTimeoutLocked(timeoutTime) 设置超时广播消息；
- 然后在step2根据广播处理情况来处理：
- 当广播接收者等待时间过长，则调用broadcastTimeoutLocked(false);
- 当，cancelBroadcastTimeoutLocked
2.2.2 setBroadcastTimeoutLocked
final void setBroadcastTimeoutLocked(long timeoutTime) {if (! mPendingBroadcastTimeoutMessage) {Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);mHandler.sendMessageAtTime(msg, timeoutTime);mPendingBroadcastTimeoutMessage = true;}
}
设置定时广播BROADCAST_TIMEOUT_MSG，即当前往后推mTimeoutPeriod时间广播还没处理完毕，则进入广播超时流程。
- 对于前台广播，则超时为
BROADCAST_FG_TIMEOUT，即timeout=10s； - 对于后台广播，则超时为
BROADCAST_BG_TIMEOUT，即timeout=60s。
2.2.3 cancelBroadcastTimeoutLocked
final void cancelBroadcastTimeoutLocked() {if (mPendingBroadcastTimeoutMessage) {mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);mPendingBroadcastTimeoutMessage = false;}
}
移除广播超时消息BROADCAST_TIMEOUT_MSG
2.2.4 BROADCAST_TIMEOUT_MSG
到此不难理解，当BROADCAST_TIMEOUT_MSG消息成功发送时，则AMS中的mHandler收到该消息则触发调用serviceTimeout。
private final class BroadcastHandler extends Handler {public void handleMessage(Message msg) {switch (msg.what) {case BROADCAST_TIMEOUT_MSG: {synchronized (mService) {//【见小节2.2.5】broadcastTimeoutLocked(true);}} break;...}...}
}
2.2.5 broadcastTimeoutLocked
[-> BroadcastRecord.java]
final void broadcastTimeoutLocked(boolean fromMsg) {if (fromMsg) {mPendingBroadcastTimeoutMessage = false;}if (mOrderedBroadcasts.size() == 0) {return;}long now = SystemClock.uptimeMillis();BroadcastRecord r = mOrderedBroadcasts.get(0);if (fromMsg) {if (mService.mDidDexOpt) {//延迟timeouts直到dexopt结束mService.mDidDexOpt = false;long timeoutTime = SystemClock.uptimeMillis() + mTimeoutPeriod;setBroadcastTimeoutLocked(timeoutTime);return;}if (!mService.mProcessesReady) {//当系统还没有准备就绪时，广播处理流程中不存在广播超时return;}long timeoutTime = r.receiverTime + mTimeoutPeriod;if (timeoutTime > now) {//过早的timeout，重新设置广播超时setBroadcastTimeoutLocked(timeoutTime);return;}}BroadcastRecord br = mOrderedBroadcasts.get(0);if (br.state == BroadcastRecord.WAITING_SERVICES) {//广播已经处理完成，但需要等待已启动service执行完成。当等待足够时间，则处理下一条广播。br.curComponent = null;br.state = BroadcastRecord.IDLE;processNextBroadcast(false);return;}r.receiverTime = now;//当前BroadcastRecord的anr次数执行加1操作r.anrCount++;if (r.nextReceiver <= 0) {return;}ProcessRecord app = null;String anrMessage = null;Object curReceiver = r.receivers.get(r.nextReceiver-1);//根据情况记录广播接收者丢弃的EventLoglogBroadcastReceiverDiscardLocked(r);if (curReceiver instanceof BroadcastFilter) {BroadcastFilter bf = (BroadcastFilter)curReceiver;if (bf.receiverList.pid != 0&& bf.receiverList.pid != ActivityManagerService.MY_PID) {synchronized (mService.mPidsSelfLocked) {app = mService.mPidsSelfLocked.get(bf.receiverList.pid);}}} else {app = r.curApp;}if (app != null) {anrMessage = "Broadcast of " + r.intent.toString();}if (mPendingBroadcast == r) {mPendingBroadcast = null;}//继续移动到下一个广播接收者finishReceiverLocked(r, r.resultCode, r.resultData,r.resultExtras, r.resultAbort, false);scheduleBroadcastsLocked();if (anrMessage != null) {//【见小节2.2.6】mHandler.post(new AppNotResponding(app, anrMessage));}
}
2.2.6 AppNotResponding
[-> BroadcastQueue.java]
private final class AppNotResponding implements Runnable {...public void run() {//【见小节3.1】mService.appNotResponding(mApp, null, null, false, mAnnotation);}
}
2.3 ContentProvider Timeout
2.3.1 AMS.appNotRespondingViaProvider
public void appNotRespondingViaProvider(IBinder connection) {enforceCallingPermission(android.Manifest.permission.REMOVE_TASKS, "appNotRespondingViaProvider()");final ContentProviderConnection conn = (ContentProviderConnection) connection;if (conn == null) {return;}final ProcessRecord host = conn.provider.proc;//无法找到provider所处的进程if (host == null) {return;}final long token = Binder.clearCallingIdentity();try {//【见小节3.1】appNotResponding(host, null, null, false, "ContentProvider not responding");} finally {Binder.restoreCallingIdentity(token);}
}
Timeout时间20s
调用链：
ContentProviderClient.NotRespondingRunnable.runContextImpl.ApplicationContentResolver.appNotRespondingViaProviderActivityThread.appNotRespondingViaProviderAMP.appNotRespondingViaProviderAMS.appNotRespondingViaProvider
2.4 inputDispatching Timeout
在native层InputDispatcher.cpp中经过层层调用，此处先省略过程，后续再展开，从native层com_android_server_input_InputManagerService调用到java层InputManagerService。
2.4.1 IMS.notifyANR
[-> InputManagerService.java]
private long notifyANR(InputApplicationHandle inputApplicationHandle,InputWindowHandle inputWindowHandle, String reason) {//【见小节2.4.2】return mWindowManagerCallbacks.notifyANR(inputApplicationHandle, inputWindowHandle, reason);
}
mWindowManagerCallbacks为InputMonitor对象
2.4.2 notifyANR
[-> InputMonitor.java]
public long notifyANR(InputApplicationHandle inputApplicationHandle,InputWindowHandle inputWindowHandle, String reason) {AppWindowToken appWindowToken = null;WindowState windowState = null;boolean aboveSystem = false;synchronized (mService.mWindowMap) {if (inputWindowHandle != null) {windowState = (WindowState) inputWindowHandle.windowState;if (windowState != null) {appWindowToken = windowState.mAppToken;}}if (appWindowToken == null && inputApplicationHandle != null) {appWindowToken = (AppWindowToken)inputApplicationHandle.appWindowToken;}//输出input事件分发超时logif (windowState != null) {Slog.i(WindowManagerService.TAG, "Input event dispatching timed out "+ "sending to " + windowState.mAttrs.getTitle()+ ". Reason: " + reason);int systemAlertLayer = mService.mPolicy.windowTypeToLayerLw(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);aboveSystem = windowState.mBaseLayer > systemAlertLayer;} else if (appWindowToken != null) {Slog.i(WindowManagerService.TAG, "Input event dispatching timed out "+ "sending to application " + appWindowToken.stringName+ ". Reason: " + reason);} else {Slog.i(WindowManagerService.TAG, "Input event dispatching timed out "+ ". Reason: " + reason);}mService.saveANRStateLocked(appWindowToken, windowState, reason);}if (appWindowToken != null && appWindowToken.appToken != null) {//【见小节2.5.1】boolean abort = appWindowToken.appToken.keyDispatchingTimedOut(reason);if (! abort) {return appWindowToken.inputDispatchingTimeoutNanos;}} else if (windowState != null) {//AMP经过binder，最终调用到AMS【见小节2.4.3】long timeout = ActivityManagerNative.getDefault().inputDispatchingTimedOut(windowState.mSession.mPid, aboveSystem, reason);if (timeout >= 0) {return timeout * 1000000L; //转化为纳秒}}return 0;
}
2.4.3 AMS.inputDispatchingTimedOut
public long inputDispatchingTimedOut(int pid, final boolean aboveSystem, String reason) {...ProcessRecord proc;long timeout;synchronized (this) {synchronized (mPidsSelfLocked) {proc = mPidsSelfLocked.get(pid); //根据pid查看进程record}timeout = getInputDispatchingTimeoutLocked(proc);}//【见小节2.4.4】if (!inputDispatchingTimedOut(proc, null, null, aboveSystem, reason)) {return -1;}return timeout;
}
inputDispatching的超时为KEY_DISPATCHING_TIMEOUT，即timeout = 5s
2.4.4 AMS.inputDispatchingTimedOut
public boolean inputDispatchingTimedOut(final ProcessRecord proc,final ActivityRecord activity, final ActivityRecord parent,final boolean aboveSystem, String reason) {...final String annotation;if (reason == null) {annotation = "Input dispatching timed out";} else {annotation = "Input dispatching timed out (" + reason + ")";}if (proc != null) {...mHandler.post(new Runnable() {public void run() {//【见小节3.1】appNotResponding(proc, activity, parent, aboveSystem, annotation);}});}return true;
}
调用链：
InputManagerService.notifyANRInputMonitor.notifyANRAMP.inputDispatchingTimedOutAMS.inputDispatchingTimedOut
2.5 keyDispatching Timeout
keyDispatching timout与inputDispatching Timeout流畅基本一致。
调用链：
InputManagerService.notifyANRInputMonitor.notifyANRActivityRecord.Token.keyDispatchingTimedOutAMS.inputDispatchingTimedOut
Token.keyDispatchingTimedOut
[-> ActivityRecord.java]
final class ActivityRecord {static class Token extends IApplicationToken.Stub {public boolean keyDispatchingTimedOut(String reason) {ActivityRecord r;ActivityRecord anrActivity;ProcessRecord anrApp;synchronized (mService) {r = tokenToActivityRecordLocked(this);if (r == null) {return false;}anrActivity = r.getWaitingHistoryRecordLocked();anrApp = r != null ? r.app : null;}return mService.inputDispatchingTimedOut(anrApp, anrActivity, r, false, reason);}...}
}
对于keyDispatching Timeout的ANR，当触发该类型ANR时，如果不再有输入事件，则不会弹出ANR对话框；只有在下一次input事件产生后5s才弹出ANR提示框。
三、ANR工作
3.1 appNotResponding
[-> ActivityManagerService.java]
final void appNotResponding(ProcessRecord app, ActivityRecord activity,ActivityRecord parent, boolean aboveSystem, final String annotation) {ArrayList<Integer> firstPids = new ArrayList<Integer>(5);SparseArray<Boolean> lastPids = new SparseArray<Boolean>(20);if (mController != null) {try {// 0 == continue, -1 = kill process immediatelyint res = mController.appEarlyNotResponding(app.processName, app.pid, annotation);if (res < 0 && app.pid != MY_PID) {app.kill("anr", true);}} catch (RemoteException e) {mController = null;Watchdog.getInstance().setActivityController(null);}}long anrTime = SystemClock.uptimeMillis();if (MONITOR_CPU_USAGE) {updateCpuStatsNow();}synchronized (this) {// PowerManager.reboot() 会阻塞很长时间，因此忽略关机时的ANRif (mShuttingDown) {Slog.i(TAG, "During shutdown skipping ANR: " + app + " " + annotation);return;} else if (app.notResponding) {Slog.i(TAG, "Skipping duplicate ANR: " + app + " " + annotation);return;} else if (app.crashing) {Slog.i(TAG, "Crashing app skipping ANR: " + app + " " + annotation);return;}app.notResponding = true;//记录ANREventLog.writeEvent(EventLogTags.AM_ANR, app.userId, app.pid,app.processName, app.info.flags, annotation);// Dump thread traces as quickly as we can, starting with "interesting" processes.firstPids.add(app.pid);int parentPid = app.pid;if (parent != null && parent.app != null && parent.app.pid > 0) parentPid = parent.app.pid;if (parentPid != app.pid) firstPids.add(parentPid);if (MY_PID != app.pid && MY_PID != parentPid) firstPids.add(MY_PID);for (int i = mLruProcesses.size() - 1; i >= 0; i--) {ProcessRecord r = mLruProcesses.get(i);if (r != null && r.thread != null) {int pid = r.pid;if (pid > 0 && pid != app.pid && pid != parentPid && pid != MY_PID) {if (r.persistent) {firstPids.add(pid);} else {lastPids.put(pid, Boolean.TRUE);}}}}}//输出ANR到main log.StringBuilder info = new StringBuilder();info.setLength(0);info.append("ANR in ").append(app.processName);if (activity != null && activity.shortComponentName != null) {info.append(" (").append(activity.shortComponentName).append(")");}info.append("\n");info.append("PID: ").append(app.pid).append("\n");if (annotation != null) {info.append("Reason: ").append(annotation).append("\n");}if (parent != null && parent != activity) {info.append("Parent: ").append(parent.shortComponentName).append("\n");}final ProcessCpuTracker processCpuTracker = new ProcessCpuTracker(true);//dump栈信息File tracesFile = dumpStackTraces(true, firstPids, processCpuTracker, lastPids,NATIVE_STACKS_OF_INTEREST);String cpuInfo = null;if (MONITOR_CPU_USAGE) {updateCpuStatsNow();synchronized (mProcessCpuTracker) {//输出各个进程的CPU使用情况cpuInfo = mProcessCpuTracker.printCurrentState(anrTime);}//输出CPU负载info.append(processCpuTracker.printCurrentLoad());info.append(cpuInfo);}info.append(processCpuTracker.printCurrentState(anrTime));Slog.e(TAG, info.toString());if (tracesFile == null) {//发送signal 3来dump栈信息Process.sendSignal(app.pid, Process.SIGNAL_QUIT);}//将anr信息添加到dropboxaddErrorToDropBox("anr", app, app.processName, activity, parent, annotation,cpuInfo, tracesFile, null);if (mController != null) {try {// 0 == show dialog, 1 = keep waiting, -1 = kill process immediatelyint res = mController.appNotResponding(app.processName, app.pid, info.toString());if (res != 0) {if (res < 0 && app.pid != MY_PID) {app.kill("anr", true);} else {synchronized (this) {mServices.scheduleServiceTimeoutLocked(app);}}return;}} catch (RemoteException e) {mController = null;Watchdog.getInstance().setActivityController(null);}}boolean showBackground = Settings.Secure.getInt(mContext.getContentResolver(),Settings.Secure.ANR_SHOW_BACKGROUND, 0) != 0;synchronized (this) {mBatteryStatsService.noteProcessAnr(app.processName, app.uid);if (!showBackground && !app.isInterestingToUserLocked() && app.pid != MY_PID) {app.kill("bg anr", true);return;}// Set the app's notResponding state, and look up the errorReportReceivermakeAppNotRespondingLocked(app,activity != null ? activity.shortComponentName : null,annotation != null ? "ANR " + annotation : "ANR",info.toString());//弹出ANR对话框Message msg = Message.obtain();HashMap<String, Object> map = new HashMap<String, Object>();msg.what = SHOW_NOT_RESPONDING_MSG;msg.obj = map;msg.arg1 = aboveSystem ? 1 : 0;map.put("app", app);if (activity != null) {map.put("activity", activity);}mUiHandler.sendMessage(msg);}
}
主要发送ANR， 则会输出
- 各个进程的CPU使用情况；
- CPU负载；
- IOWait；
- traces文件
四、其他
导致ANR常见情形：
- I/O阻塞
- 网络阻塞；
- onReceiver执行时间超过10s;
- 多线程死锁
避免ANR:
- UI线程尽量只做跟UI相关的工作
- 耗时的工作()比如数据库操作，I/O，网络操作)，采用单独的工作线程处理
- 用Handler来处理UIthread和工作thread的交互
UI线程，例如：
- Activity:onCreate(), onResume(), onDestroy(), onKeyDown(), onClick(),etc
- AsyncTask: onPreExecute(), onProgressUpdate(), onPostExecute(), onCancel,etc
- Mainthread handler: handleMessage(), post*(runnable r), etc
- …
ANR分析：需要关注CPU/IO，trace死锁等数据。
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