02.Android崩溃Crash库之App崩溃分析

目录总结

• 01.抛出异常导致崩溃分析
• 02.RuntimeInit类分析
• 03.Looper停止App就退出吗
• 04.handleApplicationCrash
• 05.native_crash如何监控
• 06.ANR是如何监控的
• 07.回过头看addErrorToDropBox

前沿

• 上一篇整体介绍了crash崩溃库崩溃重启，崩溃记录记录，查看以及分享日志等功能。
• 项目地址：https://github.com/yangchong211/YCAndroidTool
• 欢迎star，哈哈哈

01.抛出异常导致崩溃分析

• 线程中抛出异常以后的处理逻辑。

  • 一旦线程出现抛出异常，并且我们没有捕捉的情况下，JVM将调用Thread中的dispatchUncaughtException方法把异常传递给线程的未捕获异常处理器。
  • 如果没有设置uncaughtExceptionHandler，将使用线程所在的线程组来处理这个未捕获异常。线程组ThreadGroup实现了UncaughtExceptionHandler，所以可以用来处理未捕获异常。

  public final void dispatchUncaughtException(Throwable e) {
      Thread.UncaughtExceptionHandler initialUeh =
              Thread.getUncaughtExceptionPreHandler();
      if (initialUeh != null) {
          try {
              initialUeh.uncaughtException(this, e);
          } catch (RuntimeException | Error ignored) {
              // Throwables thrown by the initial handler are ignored
          }
      }
      getUncaughtExceptionHandler().uncaughtException(this, e);
  }
  
  public static UncaughtExceptionHandler getUncaughtExceptionPreHandler() {
      return uncaughtExceptionPreHandler;
  }
  
  public UncaughtExceptionHandler getUncaughtExceptionHandler() {
      return uncaughtExceptionHandler != null ?
          uncaughtExceptionHandler : group;
  }
  
  private ThreadGroup group;

• 然后看一下ThreadGroup中实现uncaughtException(Thread t, Throwable e)方法，代码如下

  • 默认情况下，线程组处理未捕获异常的逻辑是，首先将异常消息通知给父线程组，
  • 然后尝试利用一个默认的defaultUncaughtExceptionHandler来处理异常，
  • 如果没有默认的异常处理器则将错误信息输出到System.err。
  • 也就是JVM提供给我们设置每个线程的具体的未捕获异常处理器，也提供了设置默认异常处理器的方法。

  public void uncaughtException(Thread t, Throwable e) {
      if (parent != null) {
          parent.uncaughtException(t, e);
      } else {
          Thread.UncaughtExceptionHandler ueh =
              Thread.getDefaultUncaughtExceptionHandler();
          if (ueh != null) {
              ueh.uncaughtException(t, e);
          } else if (!(e instanceof ThreadDeath)) {
              System.err.print("Exception in thread \""
                               + t.getName() + "\" ");
              e.printStackTrace(System.err);
          }
      }
  }

• 既然Android遇到异常会发生崩溃，然后找一些哪里用到设置setDefaultUncaughtExceptionHandler，即可定位到RuntimeInit类。

02.RuntimeInit类分析

• 然后看一下RuntimeInit类，由于是java代码，所以首先找main方法入口。代码如下所示

  public static final void main(String[] argv) {
      enableDdms();
      if (argv.length == 2 && argv[1].equals("application")) {
          if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting application");
          redirectLogStreams();
      } else {
          if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting tool");
      }
  
      commonInit();
  
      /*
       * Now that we're running in interpreted code, call back into native code
       * to run the system.
       */
      nativeFinishInit();
  
      if (DEBUG) Slog.d(TAG, "Leaving RuntimeInit!");
  }

• 然后再来看一下commonInit()方法，看看里面做了什么操作？

  • 可以发现这里调用了setDefaultUncaughtExceptionHandler方法，设置了自定义的Handler类

  protected static final void commonInit() {
      if (DEBUG) Slog.d(TAG, "Entered RuntimeInit!");
      /*
       * set handlers; these apply to all threads in the VM. Apps can replace
       * the default handler, but not the pre handler.
       */
      LoggingHandler loggingHandler = new LoggingHandler();
      Thread.setUncaughtExceptionPreHandler(loggingHandler);
      Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler(loggingHandler));
  
      initialized = true;
  }

• 接着看一下KillApplicationHandler类，可以发现该类实现了Thread.UncaughtExceptionHandler 接口
  -

  private static class KillApplicationHandler implements Thread.UncaughtExceptionHandler {
      private final LoggingHandler mLoggingHandler;
  
      @Override
      public void uncaughtException(Thread t, Throwable e) {
          try {
              ensureLogging(t, e);
  
              // Don't re-enter -- avoid infinite loops if crash-reporting crashes.
              if (mCrashing) return;
              mCrashing = true;
  
              // Try to end profiling. If a profiler is running at this point, and we kill the
              // process (below), the in-memory buffer will be lost. So try to stop, which will
              // flush the buffer. (This makes method trace profiling useful to debug crashes.)
              if (ActivityThread.currentActivityThread() != null) {
                  ActivityThread.currentActivityThread().stopProfiling();
              }
  
              // Bring up crash dialog, wait for it to be dismissed
              ActivityManager.getService().handleApplicationCrash(
                      mApplicationObject, new ApplicationErrorReport.ParcelableCrashInfo(e));
          } catch (Throwable t2) {
              if (t2 instanceof DeadObjectException) {
                  // System process is dead; ignore
              } else {
                  try {
                      Clog_e(TAG, "Error reporting crash", t2);
                  } catch (Throwable t3) {
                      // Even Clog_e() fails!  Oh well.
                  }
              }
          } finally {
              // Try everything to make sure this process goes away.
              Process.killProcess(Process.myPid());
              System.exit(10);
          }
      }
  }

• 得出结论

  • 其实在fork出app进程的时候，系统已经为app设置了一个异常处理，并且最终崩溃后会直接导致执行该handler的finallly方法最后杀死app直接退出app。如果你要自己处理，你可以自己实现Thread.UncaughtExceptionHandler。

03.Looper停止App就退出吗

• looper如果停止了，那么app会退出吗，先做个实验看一下。代码如下所示

  • 可以发现调用这句话，是会让app退出的。会报错崩溃日志是：java.lang.IllegalStateException: Main thread not allowed to quit.

  Looper.getMainLooper().quit();
  //下面这种是安全退出
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
      Looper.getMainLooper().quitSafely();
  }

• 然后看一下Looper中quit方法源码

  • Looper的quit方法源码如下：

  public void quit() {
      mQueue.quit(false);
  }

  • Looper的quitSafely方法源码如下：

  public void quitSafely() {
      mQueue.quit(true);
  }

• 以上两个方法中mQueue是MessageQueue类型的对象，二者都调用了MessageQueue中的quit方法，MessageQueue的quit方法源码如下:

  • 可以发现上面调用了quit方法，即会出现出现崩溃，主要原因是因为调用prepare()-->new Looper(true)--->new MessageQueue(true)--->mQuitAllowed设置为true

  void quit(boolean safe) {
      if (!mQuitAllowed) {
          throw new IllegalStateException("Main thread not allowed to quit.");
      }
  
      synchronized (this) {
          if (mQuitting) {
              return;
          }
          mQuitting = true;
  
          if (safe) {
              removeAllFutureMessagesLocked();
          } else {
              removeAllMessagesLocked();
          }
  
          // We can assume mPtr != 0 because mQuitting was previously false.
          nativeWake(mPtr);
      }
  }

• 通过观察以上源码我们可以发现:

  • 当我们调用Looper的quit方法时，实际上执行了MessageQueue中的removeAllMessagesLocked方法，该方法的作用是把MessageQueue消息池中所有的消息全部清空，无论是延迟消息（延迟消息是指通过sendMessageDelayed或通过postDelayed等方法发送的需要延迟执行的消息）还是非延迟消息。
  • 当我们调用Looper的quitSafely方法时，实际上执行了MessageQueue中的removeAllFutureMessagesLocked方法，通过名字就可以看出，该方法只会清空MessageQueue消息池中所有的延迟消息，并将消息池中所有的非延迟消息派发出去让Handler去处理，quitSafely相比于quit方法安全之处在于清空消息之前会派发所有的非延迟消息。
  • 无论是调用了quit方法还是quitSafely方法只会，Looper就不再接收新的消息。即在调用了Looper的quit或quitSafely方法之后，消息循环就终结了，这时候再通过Handler调用sendMessage或post等方法发送消息时均返回false，表示消息没有成功放入消息队列MessageQueue中，因为消息队列已经退出了。
  • 需要注意的是Looper的quit方法从API Level 1就存在了，但是Looper的quitSafely方法从API Level 18才添加进来。

04.handleApplicationCrash

• 在KillApplicationHandler类中的uncaughtException方法，可以看到ActivityManager.getService().handleApplicationCrash被调用，那么这个是用来做什么的呢？

  • ActivityManager.getService().handleApplicationCrash-->ActivityManagerService.handleApplicationCrash-->handleApplicationCrashInner方法
  • 从下面可以看出,若传入app为null时,processName就设置为system_server

  public void handleApplicationCrash(IBinder app,
          ApplicationErrorReport.ParcelableCrashInfo crashInfo) {
      ProcessRecord r = findAppProcess(app, "Crash");
      final String processName = app == null ? "system_server"
              : (r == null ? "unknown" : r.processName);
  
      handleApplicationCrashInner("crash", r, processName, crashInfo);
  }

• 然后接着看一下handleApplicationCrashInner方法做了什么

  • 调用addErrorToDropBox将应用crash,进行封装输出。

  void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
          ApplicationErrorReport.CrashInfo crashInfo) {
  
      addErrorToDropBox(eventType, r, processName, null, null, null, null, null, crashInfo);
  
      mAppErrors.crashApplication(r, crashInfo);
  }

05.native_crash如何监控

• native_crash，顾名思义，就是native层发生的crash。其实他是通过一个NativeCrashListener线程去监控的。

  final class NativeCrashListener extends Thread {
      ...
  
      @Override
      public void run() {
          final byte[] ackSignal = new byte[1];
  
         ...
  
          // The file system entity for this socket is created with 0777 perms, owned
          // by system:system. selinux restricts things so that only crash_dump can
          // access it.
          {
              File socketFile = new File(DEBUGGERD_SOCKET_PATH);
              if (socketFile.exists()) {
                  socketFile.delete();
              }
          }
  
          try {
              FileDescriptor serverFd = Os.socket(AF_UNIX, SOCK_STREAM, 0);
              final UnixSocketAddress sockAddr = UnixSocketAddress.createFileSystem(
                      DEBUGGERD_SOCKET_PATH);
              Os.bind(serverFd, sockAddr);
              Os.listen(serverFd, 1);
              Os.chmod(DEBUGGERD_SOCKET_PATH, 0777);
  
              //1.一直循环地读peerFd文件,若发生存在,则进入consumeNativeCrashData
              while (true) {
                  FileDescriptor peerFd = null;
                  try {
                      if (MORE_DEBUG) Slog.v(TAG, "Waiting for debuggerd connection");
                      peerFd = Os.accept(serverFd, null /* peerAddress */);
                      if (MORE_DEBUG) Slog.v(TAG, "Got debuggerd socket " + peerFd);
                      if (peerFd != null) {
                          // the reporting thread may take responsibility for
                          // acking the debugger; make sure we play along.
                          //2.进入native crash数据处理流程
                          consumeNativeCrashData(peerFd);
                      }
                  } catch (Exception e) {
                      Slog.w(TAG, "Error handling connection", e);
                  } finally {
                      ...
                  }
              }
          } catch (Exception e) {
              Slog.e(TAG, "Unable to init native debug socket!", e);
          }
      }
  
      // Read a crash report from the connection
      void consumeNativeCrashData(FileDescriptor fd) {
          try {
                  ...
                  //3.启动NativeCrashReporter作为上报错误的新线程
                  final String reportString = new String(os.toByteArray(), "UTF-8");
                  (new NativeCrashReporter(pr, signal, reportString)).start();
  
          } catch (Exception e) {
              ...
          }
      }
  }

• 上报native_crash的线程-->NativeCrashReporter:

  class NativeCrashReporter extends Thread {
      ProcessRecord mApp;
      int mSignal;
      String mCrashReport;
  
      NativeCrashReporter(ProcessRecord app, int signal, String report) {
          super("NativeCrashReport");
          mApp = app;
          mSignal = signal;
          mCrashReport = report;
      }
  
      @Override
      public void run() {
          try {
              //1.包装崩溃信息
              CrashInfo ci = new CrashInfo();
              ci.exceptionClassName = "Native crash";
              ci.exceptionMessage = Os.strsignal(mSignal);
              ci.throwFileName = "unknown";
              ci.throwClassName = "unknown";
              ci.throwMethodName = "unknown";
              ci.stackTrace = mCrashReport;
  
              if (DEBUG) Slog.v(TAG, "Calling handleApplicationCrash()");
              //2.转到ams中处理,跟普通crash一致,只是类型不一样
              mAm.handleApplicationCrashInner("native_crash", mApp, mApp.processName, ci);
              if (DEBUG) Slog.v(TAG, "<-- handleApplicationCrash() returned");
          } catch (Exception e) {
              Slog.e(TAG, "Unable to report native crash", e);
          }
      }
  }

• native crash跟到这里就结束了，后面的流程就是跟application crash一样，都会走到addErrorToDropBox中，这个最后在说。

06.ANR是如何监控的

• 这里就不讨论每种anr发生后的原因和具体的流程了，直接跳到已经触发ANR的位置。AppErrors.appNotResponding:

  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 (mService.mController != null) {
          try {
              //1.判断是否继续后面的流程,还是直接kill掉当前进程
              // 0 == continue, -1 = kill process immediately
              int res = mService.mController.appEarlyNotResponding(
                      app.processName, app.pid, annotation);
              if (res < 0 && app.pid != MY_PID) {
                  app.kill("anr", true);
              }
          } catch (RemoteException e) {
              mService.mController = null;
              Watchdog.getInstance().setActivityController(null);
          }
      }
  
      //2.记录发生anr的时间
      long anrTime = SystemClock.uptimeMillis();
      //3.更新cpu使用情况
      if (ActivityManagerService.MONITOR_CPU_USAGE) {
          mService.updateCpuStatsNow();
      }
  
      //可以在设置中设置发生anr后,是弹框显示还是后台处理,默认是后台
      // Unless configured otherwise, swallow ANRs in background processes & kill the process.
      boolean showBackground = Settings.Secure.getInt(mContext.getContentResolver(),
              Settings.Secure.ANR_SHOW_BACKGROUND, 0) != 0;
  
      boolean isSilentANR;
  
      synchronized (mService) {
          ...
  
          // In case we come through here for the same app before completing
          // this one, mark as anring now so we will bail out.
          app.notResponding = true;
  
          //3.将anr写入event log中
          EventLog.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);
  
          // Don't dump other PIDs if it's a background ANR
          isSilentANR = !showBackground && !isInterestingForBackgroundTraces(app);
          if (!isSilentANR) {
              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 = mService.mLruProcesses.size() - 1; i >= 0; i--) {
                  ProcessRecord r = mService.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);
                              if (DEBUG_ANR) Slog.i(TAG, "Adding persistent proc: " + r);
                          } else if (r.treatLikeActivity) {
                              firstPids.add(pid);
                              if (DEBUG_ANR) Slog.i(TAG, "Adding likely IME: " + r);
                          } else {
                              lastPids.put(pid, Boolean.TRUE);
                              if (DEBUG_ANR) Slog.i(TAG, "Adding ANR proc: " + r);
                          }
                      }
                  }
              }
          }
  
      }
  
      // 4.将主要的anr信息写到main.log中
      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");
      }
  
      ProcessCpuTracker processCpuTracker = new ProcessCpuTracker(true);
      ArrayList<Integer> nativePids = null;
  
      // don't dump native PIDs for background ANRs unless it is the process of interest
      String[] nativeProc = null;
      if (isSilentANR) {
          for (int i = 0; i < NATIVE_STACKS_OF_INTEREST.length; i++) {
              if (NATIVE_STACKS_OF_INTEREST[i].equals(app.processName)) {
                  nativeProc = new String[] { app.processName };
                  break;
              }
          }
          int[] pid = nativeProc == null ? null : Process.getPidsForCommands(nativeProc);
          if(pid != null){
              nativePids = new ArrayList<Integer>(pid.length);
              for (int i : pid) {
                  nativePids.add(i);
              }
          }
      } else {
          nativePids = Watchdog.getInstance().getInterestingNativePids();
      }
  
      //5.dump出stacktraces文件
      // For background ANRs, don't pass the ProcessCpuTracker to
      // avoid spending 1/2 second collecting stats to rank lastPids.
      File tracesFile = ActivityManagerService.dumpStackTraces(
              true, firstPids,
              (isSilentANR) ? null : processCpuTracker,
              (isSilentANR) ? null : lastPids,
              nativePids);
  
      String cpuInfo = null;
      if (ActivityManagerService.MONITOR_CPU_USAGE) {
          //6.再次更新cpu使用情况
          mService.updateCpuStatsNow();
          synchronized (mService.mProcessCpuTracker) {
              //7.打印anr时cpu使用状态
              cpuInfo = mService.mProcessCpuTracker.printCurrentState(anrTime);
          }
          info.append(processCpuTracker.printCurrentLoad());
          info.append(cpuInfo);
      }
  
      info.append(processCpuTracker.printCurrentState(anrTime));
  
      //8.当traces文件不存在时,只能打印线程日志了
      if (tracesFile == null) {
          // There is no trace file, so dump (only) the alleged culprit's threads to the log
          Process.sendSignal(app.pid, Process.SIGNAL_QUIT);
      }
  
      ...
      //9.关键,回到了我们熟悉的addErrorToDropBox,进行错误信息包装跟上传了
      mService.addErrorToDropBox("anr", app, app.processName, activity, parent, annotation,
              cpuInfo, tracesFile, null);
  
      if (mService.mController != null) {
          try {
              //10.根据appNotResponding返回结果,看是否继续等待,还是结束当前进程
              // 0 == show dialog, 1 = keep waiting, -1 = kill process immediately
              int res = mService.mController.appNotResponding(
                      app.processName, app.pid, info.toString());
              if (res != 0) {
                  if (res < 0 && app.pid != MY_PID) {
                      app.kill("anr", true);
                  } else {
                      synchronized (mService) {
                          mService.mServices.scheduleServiceTimeoutLocked(app);
                      }
                  }
                  return;
              }
          } catch (RemoteException e) {
              mService.mController = null;
              Watchdog.getInstance().setActivityController(null);
          }
      }
  
     ...
  }

• 我们来看一下traces文件是怎么dump出来的：

  public static File dumpStackTraces(boolean clearTraces, ArrayList<Integer> firstPids,
          ProcessCpuTracker processCpuTracker, SparseArray<Boolean> lastPids,
          ArrayList<Integer> nativePids) {
      ArrayList<Integer> extraPids = null;
  
      //1.测量CPU的使用情况，以便在请求时对顶级用户进行实际的采样。
      if (processCpuTracker != null) {
          processCpuTracker.init();
          try {
              Thread.sleep(200);
          } catch (InterruptedException ignored) {
          }
  
          processCpuTracker.update();
  
          // 2.爬取顶级应用到的cpu使用情况
          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 if (DEBUG_ANR) {
                  Slog.d(TAG, "Skipping next CPU consuming process, not a java proc: "
                          + stats.pid);
              }
          }
      }
  
      //3.读取trace文件的保存目录
      File tracesFile;
      final String tracesDirProp = SystemProperties.get("dalvik.vm.stack-trace-dir", "");
      if (tracesDirProp.isEmpty()) {
          ...
          String globalTracesPath = SystemProperties.get("dalvik.vm.stack-trace-file", null);
          ...
      } else {
         ...
      }
  
      //4.传入指定目录,进入实际dump逻辑
      dumpStackTraces(tracesFile.getAbsolutePath(), firstPids, nativePids, extraPids,
              useTombstonedForJavaTraces);
      return tracesFile;
  }

• dumpStackTraces

  private static void dumpStackTraces(String tracesFile, ArrayList<Integer> firstPids,
          ArrayList<Integer> nativePids, ArrayList<Integer> extraPids,
          boolean useTombstonedForJavaTraces) {
  
      ...
      final DumpStackFileObserver observer;
      if (useTombstonedForJavaTraces) {
          observer = null;
      } else {
          // Use a FileObserver to detect when traces finish writing.
          // The order of traces is considered important to maintain for legibility.
          observer = new DumpStackFileObserver(tracesFile);
      }
  
      //我们必须在20秒内完成所有堆栈转储。
      long remainingTime = 20 * 1000;
      try {
          if (observer != null) {
              observer.startWatching();
          }
  
          // 首先收集所有最重要的pid堆栈。
          if (firstPids != null) {
              int num = firstPids.size();
              for (int i = 0; i < num; i++) {
                  if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for pid "
                          + firstPids.get(i));
                  final long timeTaken;
                  if (useTombstonedForJavaTraces) {
                      timeTaken = dumpJavaTracesTombstoned(firstPids.get(i), tracesFile, remainingTime);
                  } else {
                      timeTaken = observer.dumpWithTimeout(firstPids.get(i), remainingTime);
                  }
  
                  remainingTime -= timeTaken;
                  if (remainingTime <= 0) {
                      Slog.e(TAG, "Aborting stack trace dump (current firstPid=" + firstPids.get(i) +
                          "); deadline exceeded.");
                      return;
                  }
  
                  if (DEBUG_ANR) {
                      Slog.d(TAG, "Done with pid " + firstPids.get(i) + " in " + timeTaken + "ms");
                  }
              }
          }
  
          //接下来收集native pid的堆栈
          if (nativePids != null) {
              for (int pid : nativePids) {
                  if (DEBUG_ANR) Slog.d(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;
                  if (remainingTime <= 0) {
                      Slog.e(TAG, "Aborting stack trace dump (current native pid=" + pid +
                          "); deadline exceeded.");
                      return;
                  }
  
                  if (DEBUG_ANR) {
                      Slog.d(TAG, "Done with native pid " + pid + " in " + timeTaken + "ms");
                  }
              }
          }
  
          // 最后，从CPU跟踪器转储所有额外PID的堆栈。
          if (extraPids != null) {
              for (int pid : extraPids) {
                  if (DEBUG_ANR) Slog.d(TAG, "Collecting stacks for extra pid " + pid);
  
                  final long timeTaken;
                  if (useTombstonedForJavaTraces) {
                      timeTaken = dumpJavaTracesTombstoned(pid, tracesFile, remainingTime);
                  } else {
                      timeTaken = observer.dumpWithTimeout(pid, remainingTime);
                  }
  
                  remainingTime -= timeTaken;
                  if (remainingTime <= 0) {
                      Slog.e(TAG, "Aborting stack trace dump (current extra pid=" + pid +
                              "); deadline exceeded.");
                      return;
                  }
  
                  if (DEBUG_ANR) {
                      Slog.d(TAG, "Done with extra pid " + pid + " in " + timeTaken + "ms");
                  }
              }
          }
      } finally {
          if (observer != null) {
              observer.stopWatching();
          }
      }
  }

• 看完之后，应该可以很清楚地的明白。ANR的流程就是打印一些 ANR reason、cpu stats、线程日志，然后分别写入main.log、event.log，然后调用到addErrorToDropBox中，最后kill该进程。

07.回过头看addErrorToDropBox

• 为什么说addErrorToDropBox是殊途同归呢，因为无论是crash、native_crash、ANR或是wtf，最终都是来到这里，交由它去处理。那下面我们就来揭开它的神秘面纱吧。

  public void addErrorToDropBox(String eventType,
          ProcessRecord process, String processName, ActivityRecord activity,
          ActivityRecord parent, String subject,
          final String report, final File dataFile,
          final ApplicationErrorReport.CrashInfo crashInfo) {
      // NOTE -- this must never acquire the ActivityManagerService lock,
      // otherwise the watchdog may be prevented from resetting the system.
  
      // Bail early if not published yet
      if (ServiceManager.getService(Context.DROPBOX_SERVICE) == null) return;
      final DropBoxManager dbox = mContext.getSystemService(DropBoxManager.class);
  
      //只有这几种类型的错误,才会进行上传
      final boolean shouldReport = ("anr".equals(eventType)
              || "crash".equals(eventType)
              || "native_crash".equals(eventType)
              || "watchdog".equals(eventType));
  
      // Exit early if the dropbox isn't configured to accept this report type.
      final String dropboxTag = processClass(process) + "_" + eventType;
      //1.如果DropBoxManager没有初始化,或不是要上传的类型,则直接返回
      if (dbox == null || !dbox.isTagEnabled(dropboxTag)&& !shouldReport)
          return;
  
      ...
  
      final StringBuilder sb = new StringBuilder(1024);
      //2.添加一些头部log信息
      appendDropBoxProcessHeaders(process, processName, sb);
      //3.添加崩溃进程和界面的信息
      try {
          if (process != null) {
              //添加是否前台前程log
              sb.append("Foreground: ")
                      .append(process.isInterestingToUserLocked() ? "Yes" : "No")
                      .append("\n");
          }
          //触发该崩溃的界面,可以为null
          if (activity != null) {
              sb.append("Activity: ").append(activity.shortComponentName).append("\n");
          }
          if (parent != null && parent.app != null && parent.app.pid != process.pid) {
              sb.append("Parent-Process: ").append(parent.app.processName).append("\n");
          }
          if (parent != null && parent != activity) {
              sb.append("Parent-Activity: ").append(parent.shortComponentName).append("\n");
          }
          //定入简要信息
          if (subject != null) {
              sb.append("Subject: ").append(subject).append("\n");
          }
          sb.append("Build: ").append(Build.FINGERPRINT).append("\n");
          //是否连接了调试
          if (Debug.isDebuggerConnected()) {
              sb.append("Debugger: Connected\n");
          }
      } catch (NullPointerException e) {
         e.printStackTrace();
      } finally {
          sb.append("\n");
      }
  
  
      final String fProcessName = processName;
      final String fEventType = eventType;
      final String packageName = getErrorReportPackageName(process, crashInfo, eventType);
      Slog.i(TAG,"addErrorToDropbox, real report package is "+packageName);
  
      // Do the rest in a worker thread to avoid blocking the caller on I/O
      // (After this point, we shouldn't access AMS internal data structures.)
      Thread worker = new Thread("Error dump: " + dropboxTag) {
          @Override
          public void run() {
              //4.添加进程的状态到dropbox中
              BufferedReader bufferedReader = null;
              String line;
              try {
                  bufferedReader = new BufferedReader(new FileReader("/proc/" + pid + "/status"));
                  for (int i = 0; i < 5; i++) {
                      if ((line = bufferedReader.readLine()) != null && line.contains("State")) {
                          sb.append(line + "\n");
                          break;
                      }
                  }
              } catch (IOException e) {
                  e.printStackTrace();
              } finally {
                  if (bufferedReader != null) {
                      try {
                          bufferedReader.close();
                      } catch (IOException e) {
                          e.printStackTrace();
                      }
                  }
              }
  
              if (report != null) {
                  sb.append(report);
              }
  
              String setting = Settings.Global.ERROR_LOGCAT_PREFIX + dropboxTag;
              int lines = Settings.Global.getInt(mContext.getContentResolver(), setting, 0);
              int maxDataFileSize = DROPBOX_MAX_SIZE - sb.length()
                      - lines * RESERVED_BYTES_PER_LOGCAT_LINE;
  
              //5.将dataFile文件定入dropbox中,一般只有anr时,会将traces文件通过该参数传递进来者,其他类型都不传.
              if (dataFile != null && maxDataFileSize > 0) {
                  try {
                      sb.append(FileUtils.readTextFile(dataFile, maxDataFileSize,
                                  "\n\n[[TRUNCATED]]"));
                  } catch (IOException e) {
                      Slog.e(TAG, "Error reading " + dataFile, e);
                  }
              }
  
              //6.如果是crash类型,会传入crashInfo,此时将其写入dropbox中
              if (crashInfo != null && crashInfo.stackTrace != null) {
                  sb.append(crashInfo.stackTrace);
              }
  
              if (lines > 0) {
                  sb.append("\n");
  
                  // 7.合并几个logcat流,取最新部分log
                  InputStreamReader input = null;
                  try {
                      java.lang.Process logcat = new ProcessBuilder(
                              "/system/bin/timeout", "-k", "15s", "10s",
                              "/system/bin/logcat", "-v", "threadtime", "-b", "events", "-b", "system",
                              "-b", "main", "-b", "crash", "-t", String.valueOf(lines))
                                      .redirectErrorStream(true).start();
  
                      try { logcat.getOutputStream().close(); } catch (IOException e) {}
                      try { logcat.getErrorStream().close(); } catch (IOException e) {}
                      input = new InputStreamReader(logcat.getInputStream());
  
                      int num;
                      char[] buf = new char[8192];
                      while ((num = input.read(buf)) > 0) sb.append(buf, 0, num);
                  } catch (IOException e) {
                      Slog.e(TAG, "Error running logcat", e);
                  } finally {
                      if (input != null) try { input.close(); } catch (IOException e) {}
                  }
              }
  
              ...
  
  
              if (shouldReport) {
                  synchronized (mErrorListenerLock) {
                      try {
                          if (mIApplicationErrorListener == null) {
                              return;
                          }
                          //8.关键,在这里可以添加一个application error的接口，用来实现应用层接收崩溃信息
                          mIApplicationErrorListener.onError(fEventType,
                                  packageName, fProcessName, subject, dropboxTag
                                          + "-" + uuid, crashInfo);
                      } catch (DeadObjectException e) {
                          Slog.i(TAG, "ApplicationErrorListener.onError() E :" + e, e);
                          mIApplicationErrorListener = null;
                      } catch (Exception e) {
                          Slog.i(TAG, "ApplicationErrorListener.onError() E :" + e, e);
                      }
                  }
              }
          }
      };
  
      ...
  }

• 调用appendDropBoxProcessHeaders添加头部log信息:

  private void appendDropBoxProcessHeaders(ProcessRecord process, String processName,
          StringBuilder sb) {
      // Watchdog thread ends up invoking this function (with
      // a null ProcessRecord) to add the stack file to dropbox.
      // Do not acquire a lock on this (am) in such cases, as it
      // could cause a potential deadlock, if and when watchdog
      // is invoked due to unavailability of lock on am and it
      // would prevent watchdog from killing system_server.
      if (process == null) {
          sb.append("Process: ").append(processName).append("\n");
          return;
      }
      // Note: ProcessRecord 'process' is guarded by the service
      // instance.  (notably process.pkgList, which could otherwise change
      // concurrently during execution of this method)
      synchronized (this) {
          sb.append("Process: ").append(processName).append("\n");
          sb.append("PID: ").append(process.pid).append("\n");
          int flags = process.info.flags;
          IPackageManager pm = AppGlobals.getPackageManager();
          //添加该进程的flag
          sb.append("Flags: 0x").append(Integer.toHexString(flags)).append("\n");
          for (int ip=0; ip<process.pkgList.size(); ip++) {
              String pkg = process.pkgList.keyAt(ip);
              sb.append("Package: ").append(pkg);
              try {
                  PackageInfo pi = pm.getPackageInfo(pkg, 0, UserHandle.getCallingUserId());
                  if (pi != null) {
                      sb.append(" v").append(pi.getLongVersionCode());
                      if (pi.versionName != null) {
                          sb.append(" (").append(pi.versionName).append(")");
                      }
                  }
              } catch (RemoteException e) {
                  Slog.e(TAG, "Error getting package info: " + pkg, e);
              }
              sb.append("\n");
          }
          //如果是执行安装的app,会在log中添加此项
          if (process.info.isInstantApp()) {
              sb.append("Instant-App: true\n");
          }
      }
  }

项目地址：https://github.com/yangchong211/YCAndroidTool