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  • 深入理解 Android ANR 触发原理以及信息收集过程

    一、概述

    作为 Android 开发者，相信大家都遇到过 ANR。那么为什么会出现 ANR 呢，ANR 之后系统都做了啥。文章将对这个问题详细解说。

    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。

    埋炸弹可以理解为发送了一个延迟触发的消息（炸弹）；

    拆炸弹可以理解为将这个延迟消息（炸弹）取消了，也就不会触发了；

    引爆炸弹可以理解为延迟时间已达，开始处理延迟消息（炸弹引爆了）。

    二、Service

    先附上一张 service 启动流程图：

     

    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

    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.

    首先咱们先看 service 的启动中一个方法 realStartServiceLocked：

    // ActiveServices.java
private final void realStartServiceLocked(ServiceRecord r, ProcessRecord app, boolean execInFg) throws RemoteException {
    ...
    //发送delay消息(SERVICE_TIMEOUT_MSG)
    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 {
        ...
    }
}

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
    mAm.mHandler.sendMessageAtTime(msg,
        proc.execServicesFg ? (now+SERVICE_TIMEOUT) : (now+ SERVICE_BACKGROUND_TIMEOUT));
} 

    在 AS.realStartServiceLocked 启动 service 方法中，发送了了一个延时的关于超时的消息，这里又对 service 进行了前后台的区分：

        // How long we wait for a service to finish executing. 20s
    static final int SERVICE_TIMEOUT = 20*1000;

    // How long we wait for a service to finish executing. 200s
    static final int SERVICE_BACKGROUND_TIMEOUT = SERVICE_TIMEOUT * 10;

    2.2 拆炸弹

    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.

    // ActivityThread，这里多说一句， ApplicationThread 是其内部类
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();
            
            // 
            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 。

    // ActiveServices
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);
        ...
    }
    ...
}
    // How long we wait for a service to finish executing.
    static final int SERVICE_TIMEOUT = 20*1000;

    该方法会在 service 启动完成后移除服务超时消息 SERVICE_TIMEOUT_MSG，时间是 20s。

    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，当倒计时结束便会向该 Handler 线程发送一条信息SERVICE_TIMEOUT_MSG,

      // ActivityManagerService.java ::MainHandler
 final class MainHandler extends Handler {
        public MainHandler(Looper looper) {
            super(looper, null, true);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
　　　　　　　　......case SERVICE_TIMEOUT_MSG: {
                mServices.serviceTimeout((ProcessRecord)msg.obj);
            } break;
     }
}

     当延时时间到了之后，就会对消息进行处理，下面看下具体处理逻辑：

    oid 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--) {
    　　　　　　　// 从进程里面获取正在运行的 service
            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]”;

    2.4 前台与后台服务的区别

    系统对前台服务启动的超时为20s，而后台服务超时为200s，那么系统是如何区别前台还是后台服务呢？来看看ActiveServices的核心逻辑：

    ComponentName startServiceLocked(...) {
    final boolean callerFg;
    if (caller != null) {
        final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);
        callerFg = callerApp.setSchedGroup != ProcessList.SCHED_GROUP_BACKGROUND;
    } else {
        callerFg = true;
    }
    ...
    ComponentName cmp = startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
    return cmp;
} 

    在startService过程根据发起方进程 callerApp 所属的进程调度组来决定被启动的服务是属于前台还是后台。当发起方进程不等于ProcessList.SCHED_GROUP_BACKGROUND (后台进程组) 则认为是前台服务，否则为后台服务，并标记在ServiceRecord的成员变量createdFromFg。

    什么进程属于SCHED_GROUP_BACKGROUND调度组呢？进程调度组大体可分为TOP、前台、后台，进程优先级（Adj）和进程调度组（SCHED_GROUP）算法较为复杂，其对应关系可粗略理解为Adj等于0的进程属于Top进程组，Adj等于100或者200的进程属于前台进程组，Adj大于200的进程属于后台进程组。关于Adj的含义见下表，简单来说就是Adj>200的进程对用户来说基本是无感知，主要是做一些后台工作，故后台服务拥有更长的超时阈值，同时后台服务属于后台进程调度组，相比前台服务属于前台进程调度组，分配更少的CPU时间片。

    前台服务准确来说，是指由处于前台进程调度组的进程发起的服务。这跟常说的fg-service服务有所不同，fg-service是指挂有前台通知的服务。

    需要注意的问题，如果日志中出现 Reason: executing service com.example.baidu/.AnrService 也不一定是因为服务本身耗时导致，比如启动服务后，执行了耗时的操作，启动服务时onCreate函数或者 onStartCommand函数不能执行，超时后，仍然会造成anr

    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

    先看发送广播的逻辑：

    // ActivityManagerService.java]
public final int broadcastIntent(IApplicationThread caller,
            Intent intent, String resolvedType, IIntentReceiver resultTo,
            int resultCode, String resultData, Bundle resultExtras,
            String[] requiredPermissions, int appOp, Bundle bOptions,
            boolean serialized, boolean sticky, int userId) {
        enforceNotIsolatedCaller("broadcastIntent");
        synchronized(this) {
    　　　　　　　// 验证广播的有效性
            intent     = verifyBroadcastLocked(intent);
　　　　　　　// 获取发送广播的进程信息
            final ProcessRecord callerApp = getRecordForAppLocked(caller);
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();
            final long origId = Binder.clearCallingIdentity();
            try {
                return broadcastIntentLocked(callerApp,
                        callerApp != null ? callerApp.info.packageName : null,
                        intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
                        requiredPermissions, appOp, bOptions, serialized, sticky,
                        callingPid, callingUid, callingUid, callingPid, userId);
            } finally {
                Binder.restoreCallingIdentity(origId);
            }
        }
    }

    broadcastIntent()方法有两个布尔参数 serialized 和 sticky 来共同决定是普通广播，有序广播，还是 Sticky 广播，参数如下：

    类型serializedsticky
    sendBroadcast false false
    sendOrderedBroadcast true false
    sendStickyBroadcast false true

    说完发送广播，接下去就要讲讲讲收广播的操作了。

    首先广播发出去之后，肯定会存在一个队列里面来进行处理。

    // ActivityManagerService
  public ActivityManagerService(Context systemContext, ActivityTaskManagerService atm) {
　　　　// ...... 创建了三个队列来保存不同的广播类型
        mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
                "foreground", foreConstants, false);
        mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
                "background", backConstants, true);
        mOffloadBroadcastQueue = new BroadcastQueue(this, mHandler,
                "offload", offloadConstants, true);
        mBroadcastQueues[0] = mFgBroadcastQueue;
        mBroadcastQueues[1] = mBgBroadcastQueue;
        mBroadcastQueues[2] = mOffloadBroadcastQueue;
    
}

    在 ams 的构造函数里面，可以发现这里对广播进行了分类，分别有前台广播，后台广播，Offload 广播，并用一个新的数组将这三个队列放在一起。这里的 handler 是 MainHandler，也就是主线程的。传入是为了获取其 looper 。

        BroadcastQueue(ActivityManagerService service, Handler handler,
            String name, BroadcastConstants constants, boolean allowDelayBehindServices) {
        mService = service;
    　　　　　// 广播的 handler 主要是获取到 ams 中 handler looper 来创建的
        mHandler     = new BroadcastHandler(handler.getLooper());
        mQueueName = name;
        mDelayBehindServices = allowDelayBehindServices;
        mConstants = constants;
        mDispatcher = new BroadcastDispatcher(this, mConstants, mHandler, mService);
    }

    下面就说下处理广播的逻辑：

        private final class BroadcastHandler extends Handler {
        public BroadcastHandler(Looper looper) {
            super(looper, null, true);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BROADCAST_INTENT_MSG: {
                    if (DEBUG_BROADCAST) Slog.v(
                            TAG_BROADCAST, "Received BROADCAST_INTENT_MSG ["
                            + mQueueName + "]");
    　　　　　　　　　　　　// 开始处理广播
                    processNextBroadcast(    true);
                } break;
                case BROADCAST_TIMEOUT_MSG: {
                    synchronized (mService) {
                        broadcastTimeoutLocked(true);
                    }
                } break;
            }
        }
    }

    可以发现这里调用的是  processNextBroadcast 方法来处理广播。

    final void processNextBroadcast(boolean fromMsg) {
    synchronized(mService) {
        //part1: 处理并行广播
        while (mParallelBroadcasts.size() > 0) {
            r = mParallelBroadcasts.remove(0);
            r.dispatchTime = SystemClock.uptimeMillis();
            r.dispatchClockTime = System.currentTimeMillis();
            final int N = r.receivers.size();
            for (int i=0; i<N; i++) {
                Object target = r.receivers.get(i);
                //分发广播给已注册的receiver 
                deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false);
            }
            addBroadcastToHistoryLocked(r);//将广播添加历史统计
        }

        //part2: 处理当前有序广播
        do {
            if (mOrderedBroadcasts.size() == 0) {
                mService.scheduleAppGcsLocked(); //没有更多的广播等待处理
                if (looped) {
                    mService.updateOomAdjLocked();
                }
                return;
            }
            r = mOrderedBroadcasts.get(0); //获取串行广播的第一个广播
            boolean forceReceive = false;
            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))) {
                    broadcastTimeoutLocked(false); //当广播处理时间超时，则强制结束这条广播
                }
            }
            ...
            if (r.receivers == null || r.nextReceiver >= numReceivers
                    || r.resultAbort || forceReceive) {
                if (r.resultTo != null) {
                    //处理广播消息消息，调用到onReceive()
                    performReceiveLocked(r.callerApp, r.resultTo,
                        new Intent(r.intent), r.resultCode,
                        r.resultData, r.resultExtras, false, false, r.userId);
                }

                cancelBroadcastTimeoutLocked(); //取消BROADCAST_TIMEOUT_MSG消息
                addBroadcastToHistoryLocked(r);
                mOrderedBroadcasts.remove(0);
                continue;
            }
        } while (r == null);

        //part3: 获取下一个receiver
        r.receiverTime = SystemClock.uptimeMillis();
        if (recIdx == 0) {
            r.dispatchTime = r.receiverTime;
            r.dispatchClockTime = System.currentTimeMillis();
        }
        if (!mPendingBroadcastTimeoutMessage) {
            long timeoutTime = r.receiverTime + mTimeoutPeriod;
            setBroadcastTimeoutLocked(timeoutTime); //设置广播超时延时消息
        }

        //part4: 处理下条有序广播
        ProcessRecord app = mService.getProcessRecordLocked(targetProcess,
                info.activityInfo.applicationInfo.uid, false);
        if (app != null && app.thread != null) {
            app.addPackage(info.activityInfo.packageName,
                    info.activityInfo.applicationInfo.versionCode, mService.mProcessStats);
            processCurBroadcastLocked(r, app); //[处理串行广播]
            return;
            ...
        }

        //该receiver所对应的进程尚未启动，则创建该进程
        if ((r.curApp=mService.startProcessLocked(targetProcess,
                info.activityInfo.applicationInfo, true,
                r.intent.getFlags() | Intent.FLAG_FROM_BACKGROUND,
                "broadcast", r.curComponent,
                (r.intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) != 0, false, false))
                        == null) {
            ...
            return;
        }
    }
}

    对于广播超时处理时机：

    1. 首先在part3的过程中setBroadcastTimeoutLocked(timeoutTime) 设置超时广播消息；

    2. 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)；也就是引爆炸弹

      • 当执行完广播,则调用 cancelBroadcastTimeoutLocked; 也就是拆除炸弹

    // BroadcastQueue
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。

        // BroadcastConstants.java 
    
　　 private static final long DEFAULT_TIMEOUT = 10_000;
    // Timeout period for this broadcast queue
    public long TIMEOUT = DEFAULT_TIMEOUT;
    // Unspecified fields retain their current value rather than revert to default 超时时间还是可以设置的
    TIMEOUT = mParser.getLong(KEY_TIMEOUT, TIMEOUT);

     来看下具体时间的设置，超时设置的是 10 s。 

    3.2 拆炸弹

    broadcast跟service超时机制大抵相同：

    // 取消超时    
final void cancelBroadcastTimeoutLocked() {
        if (mPendingBroadcastTimeoutMessage) {
            // 移除消息
            mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);
            mPendingBroadcastTimeoutMessage = false;
        }
    }

    移除广播超时消息 BROADCAST_TIMEOUT_MSG，这样就把诈弹拆除了。

     3.3 引爆炸弹

    下面看下引爆炸弹的逻辑，前面我们已经介绍了 BroadcastQueue 中的 handler 的实现了，下面直接看下超时的处理逻辑：

    //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) {
        // 发送 anr 消息，带上了 anr 进程信息和 anr 消息
        mHandler.post(new AppNotResponding(app, anrMessage));
    }
}

    1. mOrderedBroadcasts已处理完成，则不会anr;

    2. 正在执行dexopt，则不会anr;

    3. 系统还没有进入ready状态(mProcessesReady=false)，则不会anr;

    4. 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;

    来看下  AppNotResponding 实现：

        private final class AppNotResponding implements Runnable {
        private final ProcessRecord mApp;
        private final String mAnnotation;

        public AppNotResponding(ProcessRecord app, String annotation) {
            mApp = app;
            mAnnotation = annotation;
        }

        @Override
        public void run() {
            mApp.appNotResponding(null, null, null, null, false, mAnnotation);
        }
    }

    最终会让 ProcessRecord 来处理 anr，并且其内部持有 ActivityManagerService 实例。

    3.4 前台与后台广播超时

    前台广播超时为10s，后台广播超时为60s，那么如何区分前台和后台广播呢？来看看AMS的核心逻辑：

    BroadcastQueue broadcastQueueForIntent(Intent intent) {
    final boolean isFg = (intent.getFlags() & Intent.FLAG_RECEIVER_FOREGROUND) != 0;
    return (isFg) ? mFgBroadcastQueue : mBgBroadcastQueue;
}

mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
        "foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
        "background", BROADCAST_BG_TIMEOUT, true);

    根据发送广播sendBroadcast(Intent intent)中的intent的flags是否包含 FLAG_RECEIVER_FOREGROUND 来决定把该广播是放入前台广播队列或者后台广播队列，前台广播队列的超时为10s，后台广播队列的超时为60s，默认情况下广播是放入后台广播队列，除非指明加上 FLAG_RECEIVER_FOREGROUND 标识。

    后台广播比前台广播拥有更长的超时阈值，同时在广播分发过程遇到后台service的启动(mDelayBehindServices)会延迟分发广播，等待service的完成，因为等待service而导致的广播ANR会被忽略掉；后台广播属于后台进程调度组，而前台广播属于前台进程调度组。简而言之，后台广播更不容易发生ANR，同时执行的速度也会更慢。

    另外，只有串行处理的广播才有超时机制，因为接收者是串行处理的，前一个receiver处理慢，会影响后一个receiver；并行广播通过一个循环一次性向所有的receiver分发广播事件，所以不存在彼此影响的问题，则没有广播超时。

    前台广播准确来说，是指位于前台广播队列的广播。

    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

    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。

    // ActivityManagerService
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
    static     final int CONTENT_PROVIDER_PUBLISH_TIMEOUT = 10*1000;

    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.

    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. MainHandler 是 AMS 的内部类。 

    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;
            ...
        }
        ...
    }
}

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");
}


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.

    五、input超时机制

    input的超时检测机制跟service、broadcast、provider截然不同，为了更好的理解input过程先来介绍两个重要线程的相关工作：

    • InputReader线程负责通过EventHub(监听目录/dev/input)读取输入事件，一旦监听到输入事件则放入到InputDispatcher的mInBoundQueue队列，并通知其处理该事件；

    • InputDispatcher线程负责将接收到的输入事件分发给目标应用窗口，分发过程使用到3个事件队列：

      • mInBoundQueue用于记录InputReader发送过来的输入事件；

      • outBoundQueue用于记录即将分发给目标应用窗口的输入事件；

      • waitQueue用于记录已分发给目标应用，且应用尚未处理完成的输入事件；

    input的超时机制并非时间到了一定就会爆炸，而是处理后续上报事件的过程才会去检测是否该爆炸，所以更像是扫雷的过程，具体如下图所示。

    1. InputReader线程通过EventHub监听底层上报的输入事件，一旦收到输入事件则将其放至mInBoundQueue队列，并唤醒InputDispatcher线程

    2. InputDispatcher开始分发输入事件，设置埋雷的起点时间。先检测是否有正在处理的事件(mPendingEvent)，如果没有则取出mInBoundQueue队头的事件，并将其赋值给mPendingEvent，且重置ANR的timeout；否则不会从mInBoundQueue中取出事件，也不会重置timeout。然后检查窗口是否就绪(checkWindowReadyForMoreInputLocked)，满足以下任一情况，则会进入扫雷状态(检测前一个正在处理的事件是否超时)，终止本轮事件分发，否则继续执行步骤3。当应用窗口准备就绪，则将mPendingEvent转移到outBoundQueue队列

      • 对于按键类型的输入事件，则outboundQueue或者waitQueue不为空，

      • 对于非按键的输入事件，则waitQueue不为空，且等待队头时间超时500ms

    3. 当outBoundQueue不为空，且应用管道对端连接状态正常，则将数据从outboundQueue中取出事件，放入waitQueue队列

    4. InputDispatcher通过socket告知目标应用所在进程可以准备开始干活

    5. App在初始化时默认已创建跟中控系统双向通信的socketpair，此时App的包工头(main线程)收到输入事件后，会层层转发到目标窗口来处理

    6. 包工头完成工作后，会通过socket向中控系统汇报工作完成，则中控系统会将该事件从waitQueue队列中移除。

    input超时机制为什么是扫雷，而非定时爆炸呢？是由于对于input来说即便某次事件执行时间超过timeout时长，只要用户后续在没有再生成输入事件，则不会触发ANR。 这里的扫雷是指当前输入系统中正在处理着某个耗时事件的前提下，后续的每一次input事件都会检测前一个正在处理的事件是否超时（进入扫雷状态），检测当前的时间距离上次输入事件分发时间点是否超过timeout时长。如果前一个输入事件，则会重置ANR的timeout，从而不会爆炸。

    到这里，关于 service ，广播，provider 的 anr 原因都讲清楚了。下面就看看是如何对 anr 信息进行收集的。

    六、appNotResponding处理流程

    不管是啥 anr ，最终都会调用到 ProcessRecord 的 appNotResponding 方法，下面来看看这个方法里面具体都做了啥：

    // ProcessRecord.java    
void appNotResponding(String activityShortComponentName, ApplicationInfo aInfo,
            String parentShortComponentName, WindowProcessController parentProcess,
            boolean aboveSystem, String annotation) {
        ArrayList<Integer> firstPids = new ArrayList<>(5);
        SparseArray<Boolean> lastPids = new SparseArray<>(20);

        mWindowProcessController.appEarlyNotResponding(annotation, () -> kill("anr", true));
　　　　　// anr 时间，实际上发生 anr 的时候，此时收集的运行堆栈有可能并不是引起 anr 的堆栈
        long anrTime = SystemClock.uptimeMillis();
        if (isMonitorCpuUsage()) {
            mService.updateCpuStatsNow();
        }

        synchronized (mService) {
            // PowerManager.reboot() can block for a long time, so ignore ANRs while shutting down.  关机时发生 anr 会被忽略，因为可能会引起长时间阻塞
            if (mService.mAtmInternal.isShuttingDown()) {
                Slog.i(TAG, "During shutdown skipping ANR: " + this + " " + annotation);
                return;
            } else if (isNotResponding()) {
                Slog.i(TAG, "Skipping duplicate ANR: " + this + " " + annotation);
                return;
            } else if (isCrashing()) {
                Slog.i(TAG, "Crashing app skipping ANR: " + this + " " + annotation);
                return;
            } else if (killedByAm) {
                Slog.i(TAG, "App already killed by AM skipping ANR: " + this + " " + annotation);
                return;
            } else if (killed) {
                Slog.i(TAG, "Skipping died app ANR: " + this + " " + annotation);
                return;
            }

            // In case we come through here for the same app before completing
            // this one, mark as anring now so we will bail out.  这样可以避免重复进入
            setNotResponding(true);
 
            // Log the ANR to the event log.  记录 anr 到 eventlog
            EventLog.writeEvent(EventLogTags.AM_ANR, userId, pid, processName, info.flags,
                    annotation);

            // Dump thread traces as quickly as we can, starting with "interesting" processes.  将当前进程添加到 firstPids 中
            firstPids.add(pid);

            // Don't dump other PIDs if it's a background ANR
            if (!isSilentAnr()) {
                int parentPid = pid;
                if (parentProcess != null && parentProcess.getPid() > 0) {
                    parentPid = parentProcess.getPid();
                }
                if (parentPid != pid) firstPids.add(parentPid);
　　　　　　　　　　// 将system_server进程添加到firstPids
                if (MY_PID != pid && MY_PID != parentPid) firstPids.add(MY_PID);

                for (int i = getLruProcessList().size() - 1; i >= 0; i--) {
                    ProcessRecord r = getLruProcessList().get(i);
                    if (r != null && r.thread != null) {
                        int myPid = r.pid;
                        if (myPid > 0 && myPid != pid && myPid != parentPid && myPid != MY_PID) {
                            if (r.isPersistent()) { 
                                firstPids.add(myPid); // 将persistent进程添加到firstPids
                                if (DEBUG_ANR) Slog.i(TAG, "Adding persistent proc: " + r);
                            } else if (r.treatLikeActivity) {
                                firstPids.add(myPid);  // 使用了 BIND_TREAT_LIKE_ACTIVITY
                                if (DEBUG_ANR) Slog.i(TAG, "Adding likely IME: " + r);
                            } else {
                                lastPids.put(myPid, Boolean.TRUE);  // 其他进程添加到lastPids
                                if (DEBUG_ANR) Slog.i(TAG, "Adding ANR proc: " + r);
                            }
                        }
                    }
                }
            }
        }

        // Log the ANR to the main log.  记录 anr 到 mainlog 
        StringBuilder info = new StringBuilder();
        info.setLength(0);
        info.append("ANR in ").append(processName);
        if (activityShortComponentName != null) {
            info.append(" (").append(activityShortComponentName).append(")");
        }
        info.append("
");
        info.append("PID: ").append(pid).append("
");
        if (annotation != null) {
            info.append("Reason: ").append(annotation).append("
");
        }
        if (parentShortComponentName != null
                && parentShortComponentName.equals(activityShortComponentName)) {
            info.append("Parent: ").append(parentShortComponentName).append("
");
        }
　　　　　// 创建 cpu tracker 对象
        ProcessCpuTracker processCpuTracker = new ProcessCpuTracker(true);

        // don't dump native PIDs for background ANRs unless it is the process of interest
        String[] nativeProcs = null;
        if (isSilentAnr()) {
            for (int i = 0; i < NATIVE_STACKS_OF_INTEREST.length; i++) {
                if (NATIVE_STACKS_OF_INTEREST[i].equals(processName)) {
                    nativeProcs = new String[] { processName };
                    break;
                }
            }
        } else {
            nativeProcs = NATIVE_STACKS_OF_INTEREST;
        }
　　　　　// 获取 native 进程
        int[] pids = nativeProcs == null ? null : Process.getPidsForCommands(nativeProcs);
        ArrayList<Integer> nativePids = null;

        if (pids != null) {
            nativePids = new ArrayList<>(pids.length);
            for (int i : pids) {
                nativePids.add(i);
            }
        }

        // For background ANRs, don't pass the ProcessCpuTracker to
        // avoid spending 1/2 second collecting stats to rank lastPids.  收集堆栈信息
        File tracesFile = ActivityManagerService.dumpStackTraces(firstPids,
                (isSilentAnr()) ? null : processCpuTracker, (isSilentAnr()) ? null : lastPids,
                nativePids);

        String cpuInfo = null;
    　　　　　// 添加 cpu 信息
            if (isMonitorCpuUsage()) {
            mService.updateCpuStatsNow();
            synchronized (mService.mProcessCpuTracker) {
                cpuInfo = mService.mProcessCpuTracker.printCurrentState(anrTime);
            }
            info.append(processCpuTracker.printCurrentLoad());
            info.append(cpuInfo);
        }

        info.append(processCpuTracker.printCurrentState(anrTime));

        Slog.e(TAG, info.toString());
        if (tracesFile == null) {
            // There is no trace file, so dump (only) the alleged culprit's threads to the log
            Process.sendSignal(pid, Process.SIGNAL_QUIT);
        }

        StatsLog.write(StatsLog.ANR_OCCURRED, uid, processName,
                activityShortComponentName == null ? "unknown": activityShortComponentName,
                annotation,
                (this.info != null) ? (this.info.isInstantApp()
                        ? StatsLog.ANROCCURRED__IS_INSTANT_APP__TRUE
                        : StatsLog.ANROCCURRED__IS_INSTANT_APP__FALSE)
                        : StatsLog.ANROCCURRED__IS_INSTANT_APP__UNAVAILABLE,
                isInterestingToUserLocked()
                        ? StatsLog.ANROCCURRED__FOREGROUND_STATE__FOREGROUND
                        : StatsLog.ANROCCURRED__FOREGROUND_STATE__BACKGROUND,
                getProcessClassEnum(),
                (this.info != null) ? this.info.packageName : "");
        final ProcessRecord parentPr = parentProcess != null
                ? (ProcessRecord) parentProcess.mOwner : null;
    　　　　// 将traces文件 和 CPU使用率信息保存到dropbox，即data/system/dropbox目录
        mService.addErrorToDropBox(    "anr", this, processName, activityShortComponentName,
                parentShortComponentName, parentPr, annotation, cpuInfo, tracesFile, null);

        if (mWindowProcessController.appNotResponding(info.toString(), () -> kill("anr", true),
                () -> {
                    synchronized (mService) {
                        mService.mServices.scheduleServiceTimeoutLocked(this);
                    }
                })) {
            return;
        }

        synchronized (mService) {
            // mBatteryStatsService can be null if the AMS is constructed with injector only. This
            // will only happen in tests.
            if (mService.mBatteryStatsService != null) {
                mService.mBatteryStatsService.noteProcessAnr(processName, uid);
            }
　　　　　　　// 杀死后台 anr 的进程
            if (isSilentAnr() && !isDebugging()) {
    
                kill(    "bg anr", true);
                return;
            }

            // Set the app's notResponding state, and look up the errorReportReceiver
            makeAppNotRespondingLocked(activityShortComponentName,
                    annotation != null ? "ANR " + annotation : "ANR", info.toString());

            // mUiHandler can be null if the AMS is constructed with injector only. This will only
            // happen in tests.
            if (mService.mUiHandler != null) {
                // Bring up the infamous App Not Responding dialog
                Message msg = Message.obtain();
                msg.what = ActivityManagerService.SHOW_NOT_RESPONDING_UI_MSG;
                msg.obj = new AppNotRespondingDialog.Data(this, aInfo, aboveSystem);
　　　　　　　　　// 发送 anr 弹窗信息
                mService.mUiHandler.sendMessage(msg);
            }
        }
    }

    /**
     * Unless configured otherwise, swallow ANRs in background processes & kill the process.
     * Non-private access is for tests only.  如果是后台 ANR 会被吞噬，不会提示 anr，
     */
    @VisibleForTesting
    boolean isSilentAnr() {
        return !getShowBackground() && !isInterestingForBackgroundTraces();
    }

    当发生ANR时, 会按顺序依次执行:

    1. 输出ANR Reason信息到EventLog. 也就是说ANR触发的时间点最接近的就是EventLog中输出的am_anr信息;

    2. 收集并输出重要进程列表中的各个线程的traces信息，该方法较耗时; 【见小节2】

    3. 输出当前各个进程的CPU使用情况以及CPU负载情况;

    4. 将traces文件和 CPU使用情况信息保存到dropbox，即data/system/dropbox目录

    5. 根据进程类型,来决定直接后台杀掉,还是弹框告知用户.

    ANR输出重要进程的traces信息，这些进程包含:

    • firstPids队列：第一个是ANR进程，第二个是system_server，剩余是所有persistent进程；

    • Native队列：是指/system/bin/目录的mediaserver,sdcard 以及surfaceflinger进程；

    • lastPids队列: 是指mLruProcesses中的不属于firstPids的所有进程。

    下面看下收集各进程堆栈信息逻辑：

    // AMS
   /**
     * If a stack trace dump file is configured, dump process stack traces.
     * @param firstPids of dalvik VM processes to dump stack traces for first
     * @param lastPids of dalvik VM processes to dump stack traces for last
     * @param nativePids optional list of native pids to dump stack crawls
     */
    public static File dumpStackTraces(ArrayList<Integer> firstPids,
            ProcessCpuTracker processCpuTracker, SparseArray<Boolean> lastPids,
            ArrayList<Integer> nativePids) {
        ArrayList<Integer> extraPids = null;

        Slog.i(TAG, "dumpStackTraces pids=" + lastPids + " nativepids=" + nativePids);

        // Measure CPU usage as soon as we're called in order to get a realistic sampling
        // of the top users at the time of the request.
        if (processCpuTracker != null) {
            processCpuTracker.init();
            try {
                Thread.sleep(200); // 等待 200ms 
            } catch (InterruptedException ignored) {
            }
　　　　　　　// 测量CPU使用情况
            processCpuTracker.update();

            // We'll take the stack crawls of just the top apps using CPU. 收集 5 个最高使用 cpu 的 进程 
            final int N = processCpuTracker.countWorkingStats();
            extraPids = new ArrayList<>();
            for (int i = 0; i < N && extraPids.size() < 5; i++) {
                ProcessCpuTracker.Stats stats = processCpuTracker.getWorkingStats(i);
                if (lastPids.indexOfKey(stats.pid) >= 0) {
                    if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for extra pid " + stats.pid);
                    extraPids.add(stats.pid);
                } else {
                    Slog.i(TAG, "Skipping next CPU consuming process, not a java proc: "
                            + stats.pid);
                }
            }
        }

        final File tracesDir = new File(ANR_TRACE_DIR);
        // Each set of ANR traces is written to a separate file and dumpstate will process
        // all such files and add them to a captured bug report if they're recent enough.  每一个 anr 都保存在单独的文件中的
        maybePruneOldTraces(tracesDir);

        // NOTE: We should consider creating the file in native code atomically once we've
        // gotten rid of the old scheme of dumping and lot of the code that deals with paths
        // can be removed.  创建 anr 文件
        File tracesFile = createAnrDumpFile(tracesDir);
        if (tracesFile == null) {
            return null;
        }
　　　　　// 收集 anr 堆栈
        dumpStackTraces(tracesFile.getAbsolutePath(), firstPids, nativePids, extraPids);
        return tracesFile;
    }

　　 // 创建 anr 文件
    private static synchronized File createAnrDumpFile(File tracesDir) {
        if (sAnrFileDateFormat == null) {
            sAnrFileDateFormat = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss-SSS");
        }

        final String formattedDate = sAnrFileDateFormat.format(new Date());
    　　　　　// anr 文件名是 anr_加上时间
            final File anrFile = new File(tracesDir, "anr_" + formattedDate);
　　　　　...return anrFile;
    }
    
　　　// 收集堆栈逻辑
        public static void dumpStackTraces(String tracesFile, ArrayList<Integer> firstPids,
            ArrayList<Integer> nativePids, ArrayList<Integer> extraPids) {

        Slog.i(TAG, "Dumping to " + tracesFile);

        // We don't need any sort of inotify based monitoring when we're dumping traces via
        // tombstoned. Data is piped to an "intercept" FD installed in tombstoned so we're in full
        // control of all writes to the file in question.
　　　　　
        // We must complete all stack dumps within 20 seconds. 在 20s 里面完成堆栈收集工作，未完成也会直接退出
        long remainingTime = 20 * 1000;

        // First collect all of the stacks of the most important pids.  收集最重要的几个进程的信息
        if (firstPids != null) {
            int num = firstPids.size();
            for (int i = 0; i < num; i++) {
                Slog.i(TAG, "Collecting stacks for pid " + firstPids.get(i));
                final long timeTaken = dumpJavaTracesTombstoned(firstPids.get(i), tracesFile, remainingTime);
                remainingTime -= timeTaken;
                if (remainingTime <= 0) {
                    Slog.e(TAG, "Aborting stack trace dump (current firstPid=" + firstPids.get(i) +
                           "); deadline exceeded.");
                    return;
                }
            }
        }

        // Next collect the stacks of the native pids  收集 native 堆栈
        if (nativePids != null) {
            for (int pid : nativePids) {
                Slog.i(TAG, "Collecting stacks for native pid " + pid);
                final long nativeDumpTimeoutMs = Math.min(NATIVE_DUMP_TIMEOUT_MS, remainingTime);

                final long start = SystemClock.elapsedRealtime();
                Debug.dumpNativeBacktraceToFileTimeout(
                        pid, tracesFile, (int) (nativeDumpTimeoutMs / 1000));
                final long timeTaken = SystemClock.elapsedRealtime() - start;
                remainingTime -= timeTaken;
    　　　　　　　　　　... 超时则停止收集
    
            }
        }

        // Lastly, dump stacks for all extra PIDs from the CPU tracker. 最后是前面最高的 5 个 
        if (extraPids != null) {
            for (int pid : extraPids) {
                Slog.i(TAG, "Collecting stacks for extra pid " + pid);
                final long timeTaken = dumpJavaTracesTombstoned(pid, tracesFile, remainingTime);
                remainingTime -= timeTaken;
        　　　　 ...
            }
        }
        Slog.i(TAG, "Done dumping");
    }
    该方法的主要功能，依次输出：
    1. 收集firstPids进程的stacks；

      • 第一个是发生ANR进程；

      • 第二个是system_server；

      • mLruProcesses中所有的persistent进程；

    2. 收集Native进程的stacks；(dumpNativeBacktraceToFile)

      • 依次是mediaserver,sdcard,surfaceflinger进程；

    3. 收集lastPids进程的stacks;；

      • 依次输出CPU使用率top 5的进程； 

    七、总结

    当出现ANR时，都是调用到AMS.appNotResponding()方法，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，真诚感谢 gityuan 的博客。

    参考文章 

    http://gityuan.com/2016/12/02/app-not-response/

    http://gityuan.com/2016/07/02/android-anr/

    http://gityuan.com/2017/01/01/input-anr/

    http://gityuan.com/2019/04/06/android-anr/

    树林美丽、幽暗而深邃，但我有诺言尚待实现，还要奔行百里方可沉睡。 -- 罗伯特·弗罗斯特
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  • 原文地址：https://www.cnblogs.com/huansky/p/14954020.html
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