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

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

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