// 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;
    
}

    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);
    }

    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;
            }
        }
    }

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;
        }
    }
}

// BroadcastQueue
final void setBroadcastTimeoutLocked(long timeoutTime) {
    if (! mPendingBroadcastTimeoutMessage) {
        Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
        mHandler.sendMessageAtTime(msg, timeoutTime);
        mPendingBroadcastTimeoutMessage = true;
    }
}

    // 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);

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

//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));
    }
}

    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);
        }
    }

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);

// 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;

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();
               }
               ...
           }
       }
   }    
}

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;
}

// 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("\n");
        info.append("PID: ").append(pid).append("\n");
        if (annotation != null) {
            info.append("Reason: ").append(annotation).append("\n");
        }
        if (parentShortComponentName != null
                && parentShortComponentName.equals(activityShortComponentName)) {
            info.append("Parent: ").append(parentShortComponentName).append("\n");
        }
　　　　　// 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();
}

// 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");
    }