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:比如前台服务在20s内未执行完成；
- BroadcastQueue Timeout：比如前台广播在10s内未执行完成
- ContentProvider Timeout：内容提供者,在publish过超时10s;
- InputDispatching Timeout: 输入事件分发超时5s，包括按键和触摸事件。
触发ANR的过程可分为三个步骤: 埋炸弹, 拆炸弹, 引爆炸弹
二、Service
Service Timeout是位于”ActivityManager”线程中的AMS.MainHandler收到SERVICE_TIMEOUT_MSG消息时触发。
对于Service有两类:
- 对于前台服务，则超时为SERVICE_TIMEOUT = 20s；
- 对于后台服务，则超时为SERVICE_BACKGROUND_TIMEOUT = 200s
由变量ProcessRecord.execServicesFg来决定是否前台启动
2.1 埋炸弹
文章startService流程分析详细介绍Service启动流程. 其中在Service进程attach到system_server进程的过程中会调用realStartServiceLocked()方法来埋下炸弹.
2.1.1 AS.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) {
mAm.appDiedLocked(app);
throw e;
} finally {
...
}
}
2.1.2 AS.bumpServiceExecutingLocked
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2.3.1】
mAm.mHandler.sendMessageAtTime(msg,
proc.execServicesFg ? (now+SERVICE_TIMEOUT) : (now+ SERVICE_BACKGROUND_TIMEOUT));
}
该方法的主要工作发送delay消息(SERVICE_TIMEOUT_MSG). 炸弹已埋下, 我们并不希望炸弹被引爆, 那么就需要在炸弹爆炸之前拆除炸弹.
2.2 拆炸弹
在system_server进程AS.realStartServiceLocked()调用的过程会埋下一颗炸弹, 超时没有启动完成则会爆炸. 那么什么时候会拆除这颗炸弹的引线呢? 经过Binder等层层调用进入目标进程的主线程handleCreateService()的过程.
2.2.1 AT.handleCreateService
[-> ActivityThread.java]
private void handleCreateService(CreateServiceData data) {
...
java.lang.ClassLoader cl = packageInfo.getClassLoader();
Service service = (Service) cl.loadClass(data.info.name).newInstance();
...
try {
//创建ContextImpl对象
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
//创建Application对象
Application app = packageInfo.makeApplication(false, mInstrumentation);
service.attach(context, this, data.info.name, data.token, app,
ActivityManagerNative.getDefault());
//调用服务onCreate()方法
service.onCreate();
//拆除炸弹引线[见小节2.2.2]
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
} catch (Exception e) {
...
}
}
在这个过程会创建目标服务对象,以及回调onCreate()方法, 紧接再次经过多次调用回到system_server来执行serviceDoneExecuting.
2.2.2 AS.serviceDoneExecutingLocked
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service
mAm.mHandler.removeMessages(ActivityManagerService.SERVICE_TIMEOUT_MSG, r.app);
...
}
...
}
该方法的主要工作是当service启动完成，则移除服务超时消息SERVICE_TIMEOUT_MSG。
2.3 引爆炸弹
前面介绍了埋炸弹和拆炸弹的过程, 如果在炸弹倒计时结束之前成功拆卸炸弹,那么就没有爆炸的机会, 但是世事难料. 总有些极端情况下无法即时拆除炸弹,导致炸弹爆炸, 其结果就是App发生ANR. 接下来,带大家来看看炸弹爆炸的现场:
在system_server进程中有一个Handler线程, 名叫”ActivityManager”.当倒计时结束便会向该Handler线程发送 一条信息SERVICE_TIMEOUT_MSG,
2.3.1 MainHandler.handleMessage
[-> ActivityManagerService.java ::MainHandler]
final class MainHandler extends Handler {
public void handleMessage(Message msg) {
switch (msg.what) {
case SERVICE_TIMEOUT_MSG: {
...
//【见小节2.3.2】
mServices.serviceTimeout((ProcessRecord)msg.obj);
} break;
...
}
...
}
}
2.3.2 AS.serviceTimeout
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
mAm.appNotResponding(proc, null, null, false, anrMessage);
}
}
其中anrMessage的内容为”executing service [发送超时serviceRecord信息]”;
三 BroadcastReceiver
BroadcastReceiver Timeout是位于”ActivityManager”线程中的BroadcastQueue.BroadcastHandler收到BROADCAST_TIMEOUT_MSG消息时触发。
对于广播队列有两个: foreground队列和background队列:
- 对于前台广播，则超时为BROADCAST_FG_TIMEOUT = 10s；
- 对于后台广播，则超时为BROADCAST_BG_TIMEOUT = 60s
3.1 埋炸弹
文章Android Broadcast广播机制分析详细介绍广播启动流程，通过调用 processNextBroadcast来处理广播.其流程为先处理并行广播,再处理当前有序广播,最后获取并处理下条有序广播.
3.1.1 processNextBroadcast
[-> BroadcastQueue.java]
final void processNextBroadcast(boolean fromMsg) {
synchronized(mService) {
...
//part 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3.3.2】
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;
}
//拆炸弹【见小节3.2.2】
cancelBroadcastTimeoutLocked();
}
} while (r == null);
...
//part 3: 获取下条有序广播
r.receiverTime = SystemClock.uptimeMillis();
if (!mPendingBroadcastTimeoutMessage) {
long timeoutTime = r.receiverTime + mTimeoutPeriod;
//埋炸弹【见小节3.1.2】
setBroadcastTimeoutLocked(timeoutTime);
}
...
}
}
对于广播超时处理时机：
- 首先在part3的过程中setBroadcastTimeoutLocked(timeoutTime) 设置超时广播消息；
- 然后在part2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);
- 当执行完广播,则调用cancelBroadcastTimeoutLocked;
3.1.2 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。
3.2 拆炸弹
broadcast跟service超时机制大抵相同，但有一个非常隐蔽的技能点，那就是通过静态注册的广播超时会受SharedPreferences(简称SP)的影响。
3.2.1 sendFinished
关于广播是否考虑SP的情况取决于如下代码：
public final void finish() {
if (mType == TYPE_COMPONENT) {
final IActivityManager mgr = ActivityManager.getService();
if (QueuedWork.hasPendingWork()) {
//当SP有未同步到磁盘的工作，则需等待其完成，才告知系统已完成该广播
QueuedWork.queue(new Runnable() {
public void run() {
sendFinished(mgr);
}
}, false);
} else {
sendFinished(mgr);
}
} else if (mOrderedHint && mType != TYPE_UNREGISTERED) {
final IActivityManager mgr = ActivityManager.getService();
sendFinished(mgr);
}
}
可见，只有XML静态注册的广播超时检测过程会考虑是否有SP尚未完成，动态广播并不受其影响。
3.2.2 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
3.3 引爆炸弹
3.3.1 BroadcastHandler.handleMessage
[-> BroadcastQueue.java ::BroadcastHandler]
private final class BroadcastHandler extends Handler {
public void handleMessage(Message msg) {
switch (msg.what) {
case BROADCAST_TIMEOUT_MSG: {
synchronized (mService) {
//【见小节3.3.2】
broadcastTimeoutLocked(true);
}
} break;
...
}
...
}
}
3.3.2 broadcastTimeoutLocked
[-> BroadcastRecord.java]
//fromMsg = true
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) {
mService.mDidDexOpt = false;
long timeoutTime = SystemClock.uptimeMillis() + mTimeoutPeriod;
setBroadcastTimeoutLocked(timeoutTime);
return;
}
if (!mService.mProcessesReady) {
return; //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
}
long timeoutTime = r.receiverTime + mTimeoutPeriod;
if (timeoutTime > now) {
//如果当前正在执行的receiver没有超时，则重新设置广播超时
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;
}
...
Object curReceiver = r.receivers.get(r.nextReceiver-1);
//查询App进程
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3.3.3]
mHandler.post(new AppNotResponding(app, anrMessage));
}
}
- mOrderedBroadcasts已处理完成，则不会anr;
- 正在执行dexopt，则不会anr;
- 系统还没有进入ready状态(mProcessesReady=false)，则不会anr;
- 如果当前正在执行的receiver没有超时，则重新设置广播超时，不会anr;
3.3.3 AppNotResponding
[-> BroadcastQueue.java]
private final class AppNotResponding implements Runnable {
...
public void run() {
// 进入ANR处理流程
mService.appNotResponding(mApp, null, null, false, mAnnotation);
}
}
四 ContentProvider
ContentProvider Timeout是位于”ActivityManager”线程中的AMS.MainHandler收到CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG消息时触发。
ContentProvider 超时为CONTENT_PROVIDER_PUBLISH_TIMEOUT = 10s. 这个跟前面的Service和BroadcastQueue完全不同, 由Provider进程启动过程相关.
4.1 埋炸弹
文章理解ContentProvider原理详细介绍了Provider启动流程. 埋炸弹的过程 其实是在进程创建的过程,进程创建后会调用attachApplicationLocked()进入system_server进程.
4.1.1 AMS.attachApplicationLocked
private final boolean attachApplicationLocked(IApplicationThread thread, int pid) {
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid); // 根据pid获取ProcessRecord
}
}
...
//系统处于ready状态或者该app为FLAG_PERSISTENT进程则为true
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
List<ProviderInfo> providers = normalMode ? generateApplicationProvidersLocked(app) : null;
//app进程存在正在启动中的provider,则超时10s后发送CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG消息
if (providers != null && checkAppInLaunchingProvidersLocked(app)) {
Message msg = mHandler.obtainMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG);
msg.obj = app;
mHandler.sendMessageDelayed(msg, CONTENT_PROVIDER_PUBLISH_TIMEOUT);
}
thread.bindApplication(...);
...
}
10s之后引爆该炸弹
4.2 拆炸弹
当provider成功publish之后,便会拆除该炸弹.
4.2.1 AMS.publishContentProviders
public final void publishContentProviders(IApplicationThread caller, List<ContentProviderHolder> providers) {
...
synchronized (this) {
final ProcessRecord r = getRecordForAppLocked(caller);
final int N = providers.size();
for (int i = 0; i < N; i++) {
ContentProviderHolder src = providers.get(i);
...
ContentProviderRecord dst = r.pubProviders.get(src.info.name);
if (dst != null) {
ComponentName comp = new ComponentName(dst.info.packageName, dst.info.name);
mProviderMap.putProviderByClass(comp, dst); //将该provider添加到mProviderMap
String names[] = dst.info.authority.split(";");
for (int j = 0; j < names.length; j++) {
mProviderMap.putProviderByName(names[j], dst);
}
int launchingCount = mLaunchingProviders.size();
int j;
boolean wasInLaunchingProviders = false;
for (j = 0; j < launchingCount; j++) {
if (mLaunchingProviders.get(j) == dst) {
//将该provider移除mLaunchingProviders队列
mLaunchingProviders.remove(j);
wasInLaunchingProviders = true;
j--;
launchingCount--;
}
}
//成功pubish则移除该消息
if (wasInLaunchingProviders) {
mHandler.removeMessages(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG, r);
}
synchronized (dst) {
dst.provider = src.provider;
dst.proc = r;
//唤醒客户端的wait等待方法
dst.notifyAll();
}
...
}
}
}
}
4.3 引爆炸弹
在system_server进程中有一个Handler线程, 名叫”ActivityManager”.当倒计时结束便会向该Handler线程发送 一条信息CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG,
4.3.1 MainHandler.handleMessage
[-> ActivityManagerService.java ::MainHandler]
final class MainHandler extends Handler {
public void handleMessage(Message msg) {
switch (msg.what) {
case CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG: {
...
ProcessRecord app = (ProcessRecord)msg.obj;
synchronized (ActivityManagerService.this) {
//【见小节4.3.2】
processContentProviderPublishTimedOutLocked(app);
}
} break;
...
}
...
}
}
4.3.2 AMS.processContentProviderPublishTimedOutLocked
private final void processContentProviderPublishTimedOutLocked(ProcessRecord app) {
//[见4.3.3]
cleanupAppInLaunchingProvidersLocked(app, true);
//[见小节4.3.4]
removeProcessLocked(app, false, true, "timeout publishing content providers");
}
4.3.3 AMS.cleanupAppInLaunchingProvidersLocked
boolean cleanupAppInLaunchingProvidersLocked(ProcessRecord app, boolean alwaysBad) {
boolean restart = false;
for (int i = mLaunchingProviders.size() - 1; i >= 0; i--) {
ContentProviderRecord cpr = mLaunchingProviders.get(i);
if (cpr.launchingApp == app) {
if (!alwaysBad && !app.bad && cpr.hasConnectionOrHandle()) {
restart = true;
} else {
//移除死亡的provider
removeDyingProviderLocked(app, cpr, true);
}
}
}
return restart;
}
removeDyingProviderLocked()的功能跟进程的存活息息相关：详见ContentProvider引用计数 []小节4.5]
- 对于stable类型的provider(即conn.stableCount > 0),则会杀掉所有跟该provider建立stable连接的非persistent进程.
- 对于unstable类的provider(即conn.unstableCount > 0),并不会导致client进程被级联所杀.
4.3.4 AMS.removeProcessLocked
private final boolean removeProcessLocked(ProcessRecord app, boolean callerWillRestart, boolean allowRestart, String reason) {
final String name = app.processName;
final int uid = app.uid;
//移除mProcessNames中的相应对象
removeProcessNameLocked(name, uid);
if (mHeavyWeightProcess == app) {
mHandler.sendMessage(mHandler.obtainMessage(CANCEL_HEAVY_NOTIFICATION_MSG,
mHeavyWeightProcess.userId, 0));
mHeavyWeightProcess = null;
}
boolean needRestart = false;
if (app.pid > 0 && app.pid != MY_PID) {
int pid = app.pid;
synchronized (mPidsSelfLocked) {
mPidsSelfLocked.remove(pid);
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
}
...
boolean willRestart = false;
if (app.persistent && !app.isolated) {
if (!callerWillRestart) {
willRestart = true;
} else {
needRestart = true;
}
}
app.kill(reason, true); //杀进程
handleAppDiedLocked(app, willRestart, allowRestart);
if (willRestart) {
removeLruProcessLocked(app);
addAppLocked(app.info, false, null /* ABI override */);
}
} else {
mRemovedProcesses.add(app);
}
return needRestart;
}
五、总结
当出现ANR时，都是调用到AMS.appNotResponding()方法，详细过程见文章理解Android ANR的信息收集过程. 当然这里介绍的provider例外.
Timeout时长
- 对于前台服务，则超时为SERVICE_TIMEOUT = 20s；
- 对于后台服务，则超时为SERVICE_BACKGROUND_TIMEOUT = 200s
- 对于前台广播，则超时为BROADCAST_FG_TIMEOUT = 10s；
- 对于后台广播，则超时为BROADCAST_BG_TIMEOUT = 60s;
- ContentProvider超时为CONTENT_PROVIDER_PUBLISH_TIMEOUT = 10s;
超时检测
Service超时检测机制：
- 超过一定时间没有执行完相应操作来触发移除延时消息，则会触发anr;
BroadcastReceiver超时检测机制：
- 有序广播的总执行时间超过 2* receiver个数 * timeout时长，则会触发anr;
- 有序广播的某一个receiver执行过程超过 timeout时长，则会触发anr;
另外:
- 对于Service, Broadcast, Input发生ANR之后,最终都会调用AMS.appNotResponding;
- 对于provider,在其进程启动时publish过程可能会出现ANR, 则会直接杀进程以及清理相应信息,而不会弹出ANR的对话框. appNotRespondingViaProvider()过程会走appNotResponding(), 这个就不介绍了，很少使用，由用户自定义超时时间.
最后
如果你看到了这里，觉得文章写得不错就点个赞呗？如果你觉得那里值得改进的，请给我留言。一定会认真查询，修正不足。谢谢。
最后针对Android开发的同行，小编这边给大家整理了一些资料，其中分享内容包括但不限于【高级UI、性能优化、移动架构师、NDK、混合式开发（ReactNative+Weex）微信小程序、Flutter等全方面的Android进阶实践技术】希望能帮助大家学习提升进阶，也节省大家在网上搜索资料的时间来学习，也是可以分享给身边好友一起学习的！
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最近刚留意到简书点赞可以有好几种赞，长按点赞按钮就会有选项，大家点赞的时候，麻烦点个超赞，让我感受下这个功能……
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