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