理解Android Crash处理流程

Posted by Gityuan on June 24, 2016

基于Android 6.0的源码剖析, 分析Android应用Crash是如何处理的。

/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
/frameworks/base/core/java/android/app/ActivityManagerNative.java (含内部类AMP)
/frameworks/base/core/java/android/app/ApplicationErrorReport.java

/frameworks/base/services/core/java/com/android/server/
    - am/ActivityManagerService.java
    - am/ProcessRecord.java
    - am/ActivityRecord.java
    - am/ActivityStackSupervisor.java
    - am/ActivityStack.java
    - am/ActivityRecord.java
    - am/BroadcastQueue.java
    - wm/WindowManagerService.java

/libcore/libart/src/main/java/java/lang/Thread.java

一、概述

App crash(全称Application crash), 对于Crash可分为native crash和framework crash(包含app crash在内),对于crash相信很多app开发者都会遇到,那么上层什么时候会出现crash呢,系统又是如何处理crash的呢。例如,在app大家经常使用try...catch语句,那么如果没有有效catch exception,就是导致应用crash,发生没有catch exception,系统便会来进行捕获,并进入crash流程。如果你是从事Android系统开发或者架构相关工作,或者遇到需要解系统性的疑难杂症,那么很有必要了解系统Crash处理流程,知其然还需知其所以然;如果你仅仅是App初级开发,可能本文并非很适合阅读,整个系统流程错中复杂。

在Android系统启动系列文章,已讲述过上层应用都是由Zygote fork孵化而来,分为system_server系统进程和各种应用进程,在这些进程创建之初会设置未捕获异常的处理器,当系统抛出未捕获的异常时,最终都交给异常处理器。

  • 对于system_server进程:文章Android系统启动-SystemServer上篇,system_server启动过程中由RuntimeInit.java的commonInit方法设置UncaughtHandler,用于处理未捕获异常;
  • 对于普通应用进程:文章理解Android进程创建流程 ,进程创建过程中,同样会调用RuntimeInit.java的commonInit方法设置UncaughtHandler。

1.1 crash调用链

crash流程的方法调用关系来结尾:

AMP.handleApplicationCrash
    AMS.handleApplicationCrash
        AMS.findAppProcess
        AMS.handleApplicationCrashInner
            AMS.addErrorToDropBox
            AMS.crashApplication
                AMS.makeAppCrashingLocked
                    AMS.startAppProblemLocked
                    ProcessRecord.stopFreezingAllLocked
                        ActivityRecord.stopFreezingScreenLocked
                            WMS.stopFreezingScreenLocked
                                WMS.stopFreezingDisplayLocked
                    AMS.handleAppCrashLocked
                mUiHandler.sendMessage(SHOW_ERROR_MSG)

Process.killProcess(Process.myPid());
System.exit(10);

接下来说说这个过程。

二、Crash处理流程

那么接下来以commonInit()方法为起点来展开说明。

1. RuntimeInit.commonInit

public class RuntimeInit {
    ...
    private static final void commonInit() {
        //设置默认的未捕获异常处理器,UncaughtHandler实例化过程【见小节2】
        Thread.setDefaultUncaughtExceptionHandler(new UncaughtHandler());
        ...
    }
}

setDefaultUncaughtExceptionHandler()只是将异常处理器handler对象赋给Thread成员变量,即Thread.defaultUncaughtHandler = new UncaughtHandler()。接下来看看UncaughtHandler对象实例化过程。

2. UncaughtHandler

[–>RuntimeInit.java]

private static class UncaughtHandler implements Thread.UncaughtExceptionHandler {
    //覆写接口方法
    public void uncaughtException(Thread t, Throwable e) {
        try {
            //保证crash处理过程不会重入
            if (mCrashing) return;
            mCrashing = true;

            if (mApplicationObject == null) {
                //system_server进程
                Clog_e(TAG, "*** FATAL EXCEPTION IN SYSTEM PROCESS: " + t.getName(), e);
            } else {
                //普通应用进程
                StringBuilder message = new StringBuilder();
                message.append("FATAL EXCEPTION: ").append(t.getName()).append("\n");
                final String processName = ActivityThread.currentProcessName();
                if (processName != null) {
                    message.append("Process: ").append(processName).append(", ");
                }
                message.append("PID: ").append(Process.myPid());
                Clog_e(TAG, message.toString(), e);
            }

            //启动crash对话框,等待处理完成 【见小节2.1和3】
            ActivityManagerNative.getDefault().handleApplicationCrash(
                    mApplicationObject, new ApplicationErrorReport.CrashInfo(e));
        } catch (Throwable t2) {
            ...
        } finally {
            //确保当前进程彻底杀掉【见小节11】
            Process.killProcess(Process.myPid());
            System.exit(10);
        }
    }
}
  1. 当system进程crash的信息:
    • 开头*** FATAL EXCEPTION IN SYSTEM PROCESS [线程名]
    • 接着输出发生crash时的调用栈信息;
  2. 当app进程crash时的信息:
    • 开头FATAL EXCEPTION: [线程名]
    • 紧接着 Process: [进程名], PID: [进程id]
    • 最后输出发生crash时的调用栈信息。

看到这里,你就会发现要从log中搜索crash信息,只需要搜索关键词FATAL EXCEPTION;如果需要进一步筛选只搜索系统crash信息,则可以搜索的关键词可以有多样,比如*** FATAL EXCEPTION

当输出完crash信息到logcat里面,这只是crash流程的刚开始阶段,接下来弹出crash对话框,ActivityManagerNative.getDefault()返回的是ActivityManagerProxy(简称AMP),AMP经过binder调用最终交给ActivityManagerService(简称AMS)中相应的方法去处理,故接下来调用的是AMS.handleApplicationCrash()。

2.1 CrashInfo

[-> ApplicationErrorReport.java]

public class ApplicationErrorReport implements Parcelable {
    ...
    public static class CrashInfo {
        public CrashInfo(Throwable tr) {
            StringWriter sw = new StringWriter();
            PrintWriter pw = new FastPrintWriter(sw, false, 256);
            tr.printStackTrace(pw); //输出栈trace
            pw.flush();
            stackTrace = sw.toString();
            exceptionMessage = tr.getMessage();

            Throwable rootTr = tr;
            while (tr.getCause() != null) {
                tr = tr.getCause();
                if (tr.getStackTrace() != null && tr.getStackTrace().length > 0) {
                    rootTr = tr;
                }
                String msg = tr.getMessage();
                if (msg != null && msg.length() > 0) {
                    exceptionMessage = msg;
                }
            }

            exceptionClassName = rootTr.getClass().getName();
            if (rootTr.getStackTrace().length > 0) {
                StackTraceElement trace = rootTr.getStackTrace()[0];
                throwFileName = trace.getFileName();
                throwClassName = trace.getClassName();
                throwMethodName = trace.getMethodName();
                throwLineNumber = trace.getLineNumber();
            } else {
                throwFileName = "unknown";
                throwClassName = "unknown";
                throwMethodName = "unknown";
                throwLineNumber = 0;
            }
        }
        ...
    }
}

将crash信息文件名类名方法名对应行号以及异常信息都封装到CrashInfo对象。

3. handleApplicationCrash

[–>ActivityManagerService.java]

public void handleApplicationCrash(IBinder app, ApplicationErrorReport.CrashInfo crashInfo) {
    //获取进程record对象【见小节3.1】
    ProcessRecord r = findAppProcess(app, "Crash");
    final String processName = app == null ? "system_server"
            : (r == null ? "unknown" : r.processName);
    //【见小节4】
    handleApplicationCrashInner("crash", r, processName, crashInfo);
}

关于进程名(processName):

  1. 当远程IBinder对象为空时,则进程名为system_server
  2. 当远程IBinder对象不为空,且ProcessRecord为空时,则进程名为unknown;
  3. 当远程IBinder对象不为空,且ProcessRecord不为空时,则进程名为ProcessRecord对象中相应进程名。

3.1 findAppProcess

[–>ActivityManagerService.java]

private ProcessRecord findAppProcess(IBinder app, String reason) {
    if (app == null) {
        return null;
    }

    synchronized (this) {
        final int NP = mProcessNames.getMap().size();
        for (int ip=0; ip<NP; ip++) {
            SparseArray<ProcessRecord> apps = mProcessNames.getMap().valueAt(ip);
            final int NA = apps.size();
            for (int ia=0; ia<NA; ia++) {
                ProcessRecord p = apps.valueAt(ia);
                //当找到目标进程则返回
                if (p.thread != null && p.thread.asBinder() == app) {
                    return p;
                }
            }
        }
        //如果代码执行到这里,表明无法找到应用所在的进程
        return null;
    }
}

其中 mProcessNames = new ProcessMap<ProcessRecord>();对于代码mProcessNames.getMap()返回的是mMap,而mMap= new ArrayMap<String, SparseArray<ProcessRecord>>();

知识延伸:SparseArrayArrayMap是Android专门针对内存优化而设计的取代Java API中的HashMap的数据结构。对于key是int类型则使用SparseArray,可避免自动装箱过程;对于key为其他类型则使用ArrayMapHashMap的查找和插入时间复杂度为O(1)的代价是牺牲大量的内存来实现的,而SparseArrayArrayMap性能略逊于HashMap,但更节省内存。

再回到mMap,这是以进程name为key,再以(uid为key,以ProcessRecord为Value的)结构体作为value。下面看看其get()和put()方法

//获取mMap中(name,uid)所对应的ProcessRecord
public ProcessRecord get(String name, int uid) {};
//将(name,uid, value)添加到mMap
public ProcessRecord put(String name, int uid, ProcessRecord value) {};

findAppProcess()根据app(IBinder类型)来查询相应的目标对象ProcessRecord。

有了进程记录对象ProcessRecord和进程名processName,则进入执行Crash处理方法,继续往下看。

4. handleApplicationCrashInner

[–>ActivityManagerService.java]

void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
        ApplicationErrorReport.CrashInfo crashInfo) {
    //将Crash信息写入到Event log
    EventLog.writeEvent(EventLogTags.AM_CRASH,...);
    //将错误信息添加到DropBox
    addErrorToDropBox(eventType, r, processName, null, null, null, null, null, crashInfo);
    //【见小节5】
    crashApplication(r, crashInfo);
}

其中addErrorToDropBox是将crash的信息输出到目录/data/system/dropbox。例如system_server的dropbox文件名为system_server_crash@xxx.txt (xxx代表的是时间戳)

5. crashApplication

[–>ActivityManagerService.java]

private void crashApplication(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo) {
    long timeMillis = System.currentTimeMillis();
    String shortMsg = crashInfo.exceptionClassName;
    String longMsg = crashInfo.exceptionMessage;
    String stackTrace = crashInfo.stackTrace;
    if (shortMsg != null && longMsg != null) {
        longMsg = shortMsg + ": " + longMsg;
    } else if (shortMsg != null) {
        longMsg = shortMsg;
    }

    AppErrorResult result = new AppErrorResult();
    synchronized (this) {
        // 当存在ActivityController的情况,比如monkey
        if (mController != null) {
            try {
                String name = r != null ? r.processName : null;
                int pid = r != null ? r.pid : Binder.getCallingPid();
                int uid = r != null ? r.info.uid : Binder.getCallingUid();
                //调用monkey的appCrashed
                if (!mController.appCrashed(name, pid,
                        shortMsg, longMsg, timeMillis, crashInfo.stackTrace)) {
                    if ("1".equals(SystemProperties.get(SYSTEM_DEBUGGABLE, "0"))
                            && "Native crash".equals(crashInfo.exceptionClassName)) {
                        Slog.w(TAG, "Skip killing native crashed app " + name
                                + "(" + pid + ") during testing");
                    } else {
                        Slog.w(TAG, "Force-killing crashed app " + name
                                + " at watcher's request");
                        if (r != null) {
                            r.kill("crash", true);
                        } else {
                            Process.killProcess(pid);
                            killProcessGroup(uid, pid);
                        }
                    }
                    return;
                }
            } catch (RemoteException e) {
                mController = null;
                Watchdog.getInstance().setActivityController(null);
            }
        }
        
        //清除远程调用者uid和pid信息,并保存到origId
        final long origId = Binder.clearCallingIdentity();
        ...

        //【见小节6】
        if (r == null || !makeAppCrashingLocked(r, shortMsg, longMsg, stackTrace)) {
            Binder.restoreCallingIdentity(origId);
            return;
        }

        Message msg = Message.obtain();
        msg.what = SHOW_ERROR_MSG;
        HashMap data = new HashMap();
        data.put("result", result);
        data.put("app", r);
        msg.obj = data;
        //发送消息SHOW_ERROR_MSG,弹出提示crash的对话框,等待用户选择【见小节10】
        mUiHandler.sendMessage(msg);
        //恢复远程调用者uid和pid
        Binder.restoreCallingIdentity(origId);
    }

    //进入阻塞等待,直到用户选择crash对话框"退出"或者"退出并报告"
    int res = result.get();

    Intent appErrorIntent = null;
    synchronized (this) {
        if (r != null && !r.isolated) {
            // 将崩溃的进程信息保存到mProcessCrashTimes
            mProcessCrashTimes.put(r.info.processName, r.uid,
                    SystemClock.uptimeMillis());
        }
        if (res == AppErrorDialog.FORCE_QUIT_AND_REPORT) {
            //创建action="android.intent.action.APP_ERROR",组件为r.errorReportReceiver的Intent
            appErrorIntent = createAppErrorIntentLocked(r, timeMillis, crashInfo);
        }
    }

    if (appErrorIntent != null) {
        try {
            //启动Intent为appErrorIntent的Activity
            mContext.startActivityAsUser(appErrorIntent, new UserHandle(r.userId));
        } catch (ActivityNotFoundException e) {
            Slog.w(TAG, "bug report receiver dissappeared", e);
        }
    }
}

该方法主要做的两件事:

  • 调用makeAppCrashingLocked,继续处理crash流程;
  • 发送消息SHOW_ERROR_MSG,弹出提示crash的对话框,等待用户选择;

6. makeAppCrashingLocked

[–>ActivityManagerService.java]

private boolean makeAppCrashingLocked(ProcessRecord app,
        String shortMsg, String longMsg, String stackTrace) {
    app.crashing = true;
    //封装crash信息到crashingReport对象
    app.crashingReport = generateProcessError(app,
            ActivityManager.ProcessErrorStateInfo.CRASHED, null, shortMsg, longMsg, stackTrace);
    //【见小节7】
    startAppProblemLocked(app);
    //停止屏幕冻结【见小节8】
    app.stopFreezingAllLocked();
    //【见小节9】
    return handleAppCrashLocked(app, "force-crash", shortMsg, longMsg, stackTrace);
}

7. startAppProblemLocked

[–>ActivityManagerService.java]

void startAppProblemLocked(ProcessRecord app) {
    app.errorReportReceiver = null;

    for (int userId : mCurrentProfileIds) {
        if (app.userId == userId) {
            //获取当前用户下的crash应用的error receiver【见小节7.1】
            app.errorReportReceiver = ApplicationErrorReport.getErrorReportReceiver(
                    mContext, app.info.packageName, app.info.flags);
        }
    }
    //忽略当前app的广播接收【见小节7.2】
    skipCurrentReceiverLocked(app);
}

该方法主要功能:

  • 获取当前用户下的crash应用的error receiver;
  • 忽略当前app的广播接收;

7.1 getErrorReportReceiver

[-> ApplicationErrorReport.java]

public static ComponentName getErrorReportReceiver(Context context,
        String packageName, int appFlags) {
    //检查Settings中的"send_action_app_error"是否使能错误报告的功能
    int enabled = Settings.Global.getInt(context.getContentResolver(),
            Settings.Global.SEND_ACTION_APP_ERROR, 0);
    if (enabled == 0) {
        //1.当未使能时,则直接返回
        return null;
    }

    PackageManager pm = context.getPackageManager();

    String candidate = null;
    ComponentName result = null;
    try {
        //获取该crash应用的安装器的包名
        candidate = pm.getInstallerPackageName(packageName);
    } catch (IllegalArgumentException e) {
    }

    if (candidate != null) {
        result = getErrorReportReceiver(pm, packageName, candidate);//【见下文】
        if (result != null) {
            //2.当找到该crash应用的安装器,则返回;
            return result;
        }
    }

    if ((appFlags&ApplicationInfo.FLAG_SYSTEM) != 0) {
        //该系统属性名为"ro.error.receiver.system.apps"
        candidate = SystemProperties.get(SYSTEM_APPS_ERROR_RECEIVER_PROPERTY);
        result = getErrorReportReceiver(pm, packageName, candidate);//【见下文】
        if (result != null) {
            //3.当crash应用是系统应用时,且系统属性指定error receiver时,则返回;
            return result;
        }
    }

    //该默认属性名为"ro.error.receiver.default"
    candidate = SystemProperties.get(DEFAULT_ERROR_RECEIVER_PROPERTY);
    //4.当默认属性值指定error receiver时,则返回;
    return getErrorReportReceiver(pm, packageName, candidate); //【见下文】
}

getErrorReportReceiver:这是同名不同输入参数的另一个方法:

static ComponentName getErrorReportReceiver(PackageManager pm, String errorPackage,
        String receiverPackage) {
    if (receiverPackage == null || receiverPackage.length() == 0) {
        return null;
    }

    //当安装应用程序的安装器Crash,则直接返回
    if (receiverPackage.equals(errorPackage)) {
        return null;
    }

    //ACTION_APP_ERROR值为"android.intent.action.APP_ERROR"
    Intent intent = new Intent(Intent.ACTION_APP_ERROR);
    intent.setPackage(receiverPackage);
    ResolveInfo info = pm.resolveActivity(intent, 0);
    if (info == null || info.activityInfo == null) {
        return null;
    }
    //创建包名为receiverPackage的组件
    return new ComponentName(receiverPackage, info.activityInfo.name);
}

7.2 skipCurrentReceiverLocked

[–>ActivityManagerService.java]

void skipCurrentReceiverLocked(ProcessRecord app) {
    for (BroadcastQueue queue : mBroadcastQueues) {
        queue.skipCurrentReceiverLocked(app);  //【见小节7.2.1】
    }
}
7.2.1 skipCurrentReceiverLocked

[-> BroadcastQueue.java]

public void skipCurrentReceiverLocked(ProcessRecord app) {
    BroadcastRecord r = null;
    //查看app进程中的广播
    if (mOrderedBroadcasts.size() > 0) {
        BroadcastRecord br = mOrderedBroadcasts.get(0);
        if (br.curApp == app) {
            r = br;
        }
    }
    if (r == null && mPendingBroadcast != null && mPendingBroadcast.curApp == app) {
        r = mPendingBroadcast;
    }

    if (r != null) {
        //结束app进程的广播结束
        finishReceiverLocked(r, r.resultCode, r.resultData,
                r.resultExtras, r.resultAbort, false);
        //广播调度
        scheduleBroadcastsLocked();
    }
}

8. PR.stopFreezingAllLocked

[-> ProcessRecord.java]

public void stopFreezingAllLocked() {
    int i = activities.size();
    while (i > 0) {
        i--;
        activities.get(i).stopFreezingScreenLocked(true); //【见小节8.1】
    }
}

其中activities类型为ArrayList<ActivityRecord>,停止进程里所有的Activity

8.1. AR.stopFreezingScreenLocked

[-> ActivityRecord.java]

public void stopFreezingScreenLocked(boolean force) {
    if (force || frozenBeforeDestroy) {
        frozenBeforeDestroy = false;
        //mWindowManager类型为WMS //【见小节8.1.1】
        service.mWindowManager.stopAppFreezingScreen(appToken, force);
    }
}

其中appToken是IApplication.Stub类型,即WindowManager的token。

8.1.1 WMS.stopFreezingScreenLocked

[-> WindowManagerService.java]

@Override
public void stopFreezingScreen() {
    //权限检查
    if (!checkCallingPermission(android.Manifest.permission.FREEZE_SCREEN,
            "stopFreezingScreen()")) {
        throw new SecurityException("Requires FREEZE_SCREEN permission");
    }

    synchronized(mWindowMap) {
        if (mClientFreezingScreen) {
            mClientFreezingScreen = false;
            mLastFinishedFreezeSource = "client";
            final long origId = Binder.clearCallingIdentity();
            try {
                stopFreezingDisplayLocked(); //【见流程8.1.1.1】
            } finally {
                Binder.restoreCallingIdentity(origId);
            }
        }
    }
}
8.1.1.1 WMS.stopFreezingDisplayLocked

[-> WindowManagerService.java]

private void stopFreezingDisplayLocked() {
    if (!mDisplayFrozen) {
        return; //显示没有冻结,则直接返回
    }

    //往往跟屏幕旋转相关
    ...

    mDisplayFrozen = false;
    //从上次冻屏到现在的总时长
    mLastDisplayFreezeDuration = (int)(SystemClock.elapsedRealtime() - mDisplayFreezeTime);

    //移除冻屏的超时消息
    mH.removeMessages(H.APP_FREEZE_TIMEOUT);
    mH.removeMessages(H.CLIENT_FREEZE_TIMEOUT);

    boolean updateRotation = false;
    //获取默认的DisplayContent
    final DisplayContent displayContent = getDefaultDisplayContentLocked();
    final int displayId = displayContent.getDisplayId();
    ScreenRotationAnimation screenRotationAnimation =
            mAnimator.getScreenRotationAnimationLocked(displayId);

    //屏幕旋转动画的相关操作
    if (CUSTOM_SCREEN_ROTATION && screenRotationAnimation != null
            && screenRotationAnimation.hasScreenshot()) {
        DisplayInfo displayInfo = displayContent.getDisplayInfo();
        boolean isDimming = displayContent.isDimming();
        if (!mPolicy.validateRotationAnimationLw(mExitAnimId, mEnterAnimId, isDimming)) {
            mExitAnimId = mEnterAnimId = 0;
        }
        //加载动画最大时长为10s
        if (screenRotationAnimation.dismiss(mFxSession, MAX_ANIMATION_DURATION,
                getTransitionAnimationScaleLocked(), displayInfo.logicalWidth,
                    displayInfo.logicalHeight, mExitAnimId, mEnterAnimId)) {
            scheduleAnimationLocked();
        } else {
            screenRotationAnimation.kill();
            mAnimator.setScreenRotationAnimationLocked(displayId, null);
            updateRotation = true;
        }
    } else {
        if (screenRotationAnimation != null) {
            screenRotationAnimation.kill();
            mAnimator.setScreenRotationAnimationLocked(displayId, null);
        }
        updateRotation = true;
    }
    //经过层层调用到InputManagerService服务,IMS服务使能输入事件分发功能
    mInputMonitor.thawInputDispatchingLw();

    boolean configChanged;
    //当display被冻结时不再计算屏幕方向,以避免不连续的状态。
    configChanged = updateOrientationFromAppTokensLocked(false);

    //display冻结时,执行gc操作
    mH.removeMessages(H.FORCE_GC);
    mH.sendEmptyMessageDelayed(H.FORCE_GC, 2000);

    //mScreenFrozenLock的类型为PowerManager.WakeLock,即释放屏幕冻结的锁
    mScreenFrozenLock.release();

    if (updateRotation) {
        //更新当前的屏幕方向
        configChanged |= updateRotationUncheckedLocked(false);
    }

    if (configChanged) {
        //向mH发送configuraion改变的消息
        mH.sendEmptyMessage(H.SEND_NEW_CONFIGURATION);
    }
}

该方法主要功能:

  1. 处理屏幕旋转相关逻辑;
  2. 移除冻屏的超时消息;
  3. 屏幕旋转动画的相关操作;
  4. 使能输入事件分发功能;
  5. display冻结时,执行gc操作;
  6. 更新当前的屏幕方向;
  7. 向mH发送configuraion改变的消息。

9.AMS.handleAppCrashLocked

[-> ActivityManagerService.java]

private boolean handleAppCrashLocked(ProcessRecord app, String reason,
        String shortMsg, String longMsg, String stackTrace) {
    long now = SystemClock.uptimeMillis();

    Long crashTime;
    if (!app.isolated) {
        crashTime = mProcessCrashTimes.get(app.info.processName, app.uid);
    } else {
        crashTime = null;
    }
    //当同一个进程,连续两次crash的时间间隔小于1分钟时,则认为crash太过于频繁
    if (crashTime != null && now < crashTime+ProcessList.MIN_CRASH_INTERVAL) {
        EventLog.writeEvent(EventLogTags.AM_PROCESS_CRASHED_TOO_MUCH,
                app.userId, app.info.processName, app.uid);
        //【见小节9.1】
        mStackSupervisor.handleAppCrashLocked(app);
        if (!app.persistent) {
            //不再重启非persistent进程,除非用户显式地调用
            EventLog.writeEvent(EventLogTags.AM_PROC_BAD, app.userId, app.uid,
                    app.info.processName);
            if (!app.isolated) {
                //将当前app加入到mBadProcesses
                mBadProcesses.put(app.info.processName, app.uid,
                        new BadProcessInfo(now, shortMsg, longMsg, stackTrace));
                mProcessCrashTimes.remove(app.info.processName, app.uid);
            }
            app.bad = true;
            app.removed = true;
            //移除进程的所有服务,保证不再重启【见小节9.2】
            removeProcessLocked(app, false, false, "crash");
            //恢复最顶部的Activity【见小节9.3】
            mStackSupervisor.resumeTopActivitiesLocked();
            return false;
        }
        mStackSupervisor.resumeTopActivitiesLocked();
    } else {
        //此处reason="force-crash"【见小节9.4】
        mStackSupervisor.finishTopRunningActivityLocked(app, reason);
    }

    //运行在当前进程中的所有服务的crash次数执行加1操作
    for (int i=app.services.size()-1; i>=0; i--) {
        ServiceRecord sr = app.services.valueAt(i);
        sr.crashCount++;
    }

    //当桌面应用crash,并且被三方app所取代,那么需要清空桌面应用的偏爱选项。
    final ArrayList<ActivityRecord> activities = app.activities;
    if (app == mHomeProcess && activities.size() > 0
                && (mHomeProcess.info.flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
        for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
            final ActivityRecord r = activities.get(activityNdx);
            if (r.isHomeActivity()) {
                //清空偏爱应用
                ActivityThread.getPackageManager()
                        .clearPackagePreferredActivities(r.packageName);
            }
        }
    }

    if (!app.isolated) {
        //无法记录孤立进程的crash时间点,由于他们并没有一个固定身份
        mProcessCrashTimes.put(app.info.processName, app.uid, now);
    }
    //当app存在crash的handler,那么交给其处理
    if (app.crashHandler != null) mHandler.post(app.crashHandler);
    return true;
}
  1. 当同一进程在时间间隔小于1分钟时连续两次crash,则执行的情况下:
    • 对于非persistent进程:
      • [9.1] mStackSupervisor.handleAppCrashLocked(app);
      • [9.2] removeProcessLocked(app, false, false, “crash”);
      • [9.3] mStackSupervisor.resumeTopActivitiesLocked();
    • 对于persistent进程,则只执行
      • [9.3] mStackSupervisor.resumeTopActivitiesLocked();
  2. 否则执行
    • [9.4] mStackSupervisor.finishTopRunningActivityLocked(app, reason);

9.1 ASS.handleAppCrashLocked

[-> ActivityStackSupervisor.java]

void handleAppCrashLocked(ProcessRecord app) {
    for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
        final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
        int stackNdx = stacks.size() - 1;
        while (stackNdx >= 0) {
            //调用ActivityStack【见小节9.1.1】
            stacks.get(stackNdx).handleAppCrashLocked(app);
            stackNdx--;
        }
    }
}
9.1.1 AS.handleAppCrashLocked

[-> ActivityStack.java]

void handleAppCrashLocked(ProcessRecord app) {
    for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
        final ArrayList<ActivityRecord> activities = mTaskHistory.get(taskNdx).mActivities;
        for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
            final ActivityRecord r = activities.get(activityNdx);
            if (r.app == app) {
                r.app = null;
                //结束当前activity
                finishCurrentActivityLocked(r, FINISH_IMMEDIATELY, false);
            }
        }
    }
}

这里的mTaskHistory数据类型为ArrayList,记录着所有先前的后台activities。遍历所有activities,找到位于该ProcessRecord的所有ActivityRecord,并结束该Acitivity。

9.2 AMS.removeProcessLocked

[-> ActivityManagerService.java]

private final boolean removeProcessLocked(ProcessRecord app,
        boolean callerWillRestart, boolean allowRestart, String reason) {
    final String name = app.processName;
    final int uid = app.uid;
    //从mProcessNames移除该进程
    removeProcessNameLocked(name, uid);
    ...
    if (app.pid > 0 && app.pid != MY_PID) {
        int pid = app.pid;
        synchronized (mPidsSelfLocked) {
            mPidsSelfLocked.remove(pid); //移除该pid
            mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
        }
        ...
        boolean willRestart = false;
        //对于非孤立的persistent进程设置成可重启flags
        if (app.persistent && !app.isolated) {
            if (!callerWillRestart) {
                willRestart = true;
            } else {
                needRestart = true;
            }
        }
        // 杀进程【9.2.1】
        app.kill(reason, true);
         //移除进程并清空该进程相关联的activity/service等组件 【9.2.2】
        handleAppDiedLocked(app, willRestart, allowRestart);

        if (willRestart) {
            //此处willRestart=false,不进入该分支
            removeLruProcessLocked(app);
            addAppLocked(app.info, false, null /* ABI override */);
        }
    } else {
        mRemovedProcesses.add(app);
    }
    return needRestart;
}
  • mProcessNames数据类型为ProcessMap,这是以进程名为key,记录着所有的ProcessRecord信息
  • mPidsSelfLocked数据类型为SparseArray,这是以pid为key,记录着所有的ProcessRecord信息。该对象的同步保护是通过自身锁,而非全局ActivityManager锁。
9.2.1 app.kill

[-> ProcessRecord.java]

void kill(String reason, boolean noisy) {
    if (!killedByAm) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "kill");
        if (noisy) {
            Slog.i(TAG, "Killing " + toShortString() + " (adj " + setAdj + "): " + reason);
        }
        EventLog.writeEvent(EventLogTags.AM_KILL, userId, pid, processName, setAdj, reason);
        Process.killProcessQuiet(pid); //杀进程
        Process.killProcessGroup(info.uid, pid); //杀进程组,包括native进程
        if (!persistent) {
            killed = true;
            killedByAm = true;
        }
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
    }
}

此处reason为“crash”,关于杀进程的过程见我的另一篇文章理解杀进程的实现原理.

9.2.2 handleAppDiedLocked

[-> ActivityManagerService.java]

private final void handleAppDiedLocked(ProcessRecord app,
        boolean restarting, boolean allowRestart) {
    int pid = app.pid;
    //清除应用中service/receiver/ContentProvider信息
    boolean kept = cleanUpApplicationRecordLocked(app, restarting, allowRestart, -1);
    if (!kept && !restarting) {
        removeLruProcessLocked(app);
        if (pid > 0) {
            ProcessList.remove(pid);
        }
    }

    if (mProfileProc == app) {
        clearProfilerLocked();
    }

    //清除应用中activity相关信息
    boolean hasVisibleActivities = mStackSupervisor.handleAppDiedLocked(app);

    app.activities.clear();
    ...
    if (!restarting && hasVisibleActivities && !mStackSupervisor.resumeTopActivitiesLocked()) {
        mStackSupervisor.ensureActivitiesVisibleLocked(null, 0);
    }
}

9.3 ASS.resumeTopActivitiesLocked

[-> ActivityStackSupervisor.java]

boolean resumeTopActivitiesLocked() {
    return resumeTopActivitiesLocked(null, null, null);
}

boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,
        Bundle targetOptions) {
    if (targetStack == null) {
        targetStack = mFocusedStack;
    }
    boolean result = false;
    if (isFrontStack(targetStack)) {
        //【见小节9.3.1】
        result = targetStack.resumeTopActivityLocked(target, targetOptions);
    }

    for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
        final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
        for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
            final ActivityStack stack = stacks.get(stackNdx);
            if (stack == targetStack) {
                continue; //已经启动
            }
            if (isFrontStack(stack)) {
                stack.resumeTopActivityLocked(null);
            }
        }
    }
    return result;
}

此处mFocusedStack是当前正在等待接收input事件或者正在启动下一个activity的ActivityStack

9.3.1 AS.resumeTopActivityLocked

[-> ActivityStack.java]

final boolean .resumeTopActivityLocked(ActivityRecord prev, Bundle options) {
    ...
    result = resumeTopActivityInnerLocked(prev, options);//【见小节9.3.2】
    return result;
}
9.3.2 AS.resumeTopActivityInnerLocked

[-> ActivityStack.java]

private boolean resumeTopActivityInnerLocked(ActivityRecord prev, Bundle options) {
    //找到mTaskHistory栈中第一个未处于finishing状态的Activity
    final ActivityRecord next = topRunningActivityLocked(null);

    if (mResumedActivity == next && next.state == ActivityState.RESUMED &&
                        mStackSupervisor.allResumedActivitiesComplete()) {
        //当top activity已经处于resume,则无需操作;
        return false;
    }

    if (mService.isSleepingOrShuttingDown()
            && mLastPausedActivity == next
            && mStackSupervisor.allPausedActivitiesComplete()) {
        //当正处于sleeping状态,top activity处于paused,则无需操作
        return false;
    }

    //正在启动app的activity,确保app不会被设置为stopped
    AppGlobals.getPackageManager().setPackageStoppedState(
                next.packageName, false, next.userId);
    //回调应用onResume方法
    next.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,
                            mService.isNextTransitionForward(), resumeAnimOptions);
    ...
}

该方法代码比较长,这里就简单列举几条比较重要的代码。执行完该方法,应用也便完成了activity的resume过程。

9.4 finishTopRunningActivityLocked

9.4.1 ASS.finishTopRunningActivityLocked

[-> ActivityStackSupervisor.java]

void finishTopRunningActivityLocked(ProcessRecord app, String reason) {
    for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
        final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
        final int numStacks = stacks.size();
        for (int stackNdx = 0; stackNdx < numStacks; ++stackNdx) {
            final ActivityStack stack = stacks.get(stackNdx);
            //此处reason= "force-crash"【见小节9.4.2】
            stack.finishTopRunningActivityLocked(app, reason);
        }
    }
}
9.4.2 AS.finishTopRunningActivityLocked
final void finishTopRunningActivityLocked(ProcessRecord app, String reason) {
    //找到栈顶第一个不处于finishing状态的activity
    ActivityRecord r = topRunningActivityLocked(null);
    if (r != null && r.app == app) {
        int taskNdx = mTaskHistory.indexOf(r.task);
        int activityNdx = r.task.mActivities.indexOf(r);
        //【见小节9.4.3】
        finishActivityLocked(r, Activity.RESULT_CANCELED, null, reason, false);
        --activityNdx;
        if (activityNdx < 0) {
            do {
                --taskNdx;
                if (taskNdx < 0) {
                    break;
                }
                activityNdx = mTaskHistory.get(taskNdx).mActivities.size() - 1;
            } while (activityNdx < 0);
        }
        if (activityNdx >= 0) {
            r = mTaskHistory.get(taskNdx).mActivities.get(activityNdx);
            if (r.state == ActivityState.RESUMED
                    || r.state == ActivityState.PAUSING
                    || r.state == ActivityState.PAUSED) {
                if (!r.isHomeActivity() || mService.mHomeProcess != r.app) {
                    //【见小节9.4.3】
                    finishActivityLocked(r, Activity.RESULT_CANCELED, null, reason, false);
                }
            }
        }
    }
}
9.4.3 AS.finishActivityLocked
final boolean finishActivityLocked(ActivityRecord r, int resultCode, Intent resultData,
           String reason, boolean oomAdj) {
    if (r.finishing) {
        return false; //正在finishing则返回
    }
    //设置finish状态的activity不可见
    r.makeFinishingLocked();
    //暂停key的分发事件
    r.pauseKeyDispatchingLocked();

    mWindowManager.prepareAppTransition(endTask
            ? AppTransition.TRANSIT_TASK_CLOSE
            : AppTransition.TRANSIT_ACTIVITY_CLOSE, false);

    mWindowManager.setAppVisibility(r.appToken, false);
    //回调activity的onPause方法
    startPausingLocked(false, false, false, false);
    ...
}

该方法最终会回调到activity的pause方法。

执行到这,我们还回过来看小节5.crashApplication中,处理完makeAppCrashingLocked,则会再发送消息SHOW_ERROR_MSG,弹出提示crash的对话框,接下来再看看该过程。

10. UiHandler

通过mUiHandler发送message,且消息的msg.waht=SHOW_ERROR_MSG,接下来进入UiHandler来看看handleMessage的处理过程。

[-> ActivityManagerService.java]

final class UiHandler extends Handler {
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case SHOW_ERROR_MSG: {
           HashMap<String, Object> data = (HashMap<String, Object>) msg.obj;
           synchronized (ActivityManagerService.this) {
               ProcessRecord proc = (ProcessRecord)data.get("app");
               AppErrorResult res = (AppErrorResult) data.get("result");
              、
               boolean isBackground = (UserHandle.getAppId(proc.uid)
                       >= Process.FIRST_APPLICATION_UID
                       && proc.pid != MY_PID);
                ...

               if (mShowDialogs && !mSleeping && !mShuttingDown) {
                   //创建提示crash对话框,等待用户选择,5分钟操作等待。
                   Dialog d = new AppErrorDialog(mContext,
                           ActivityManagerService.this, res, proc);
                   d.show();
                   proc.crashDialog = d;
               } else {
                   //当处于sleep状态,则默认选择退出。
                   if (res != null) {
                       res.set(0);
                   }
               }
           }
        } break;
        ...
    }
}

在发生crash时,默认系统会弹出提示crash的对话框,并阻塞等待用户选择是“退出”或 “退出并报告”,当用户不做任何选择时5min超时后,默认选择“退出”,当手机休眠时也默认选择“退出”。到这里也并没有真正结束,在小节2.uncaughtException中在finnally语句块还有一个杀进程的动作。

11. killProcess

Process.killProcess(Process.myPid());
System.exit(10);

通过finnally语句块保证能执行并彻底杀掉Crash进程,关于杀进程的过程见我的另一篇文章理解杀进程的实现原理.。当Crash进程被杀后,并没有完全结束,还有Binder死亡通知的流程还没有处理完成。

12. 小结

当进程抛出未捕获异常时,则系统会处理该异常并进入crash处理流程。

app_crash

其中最为核心的工作图中红色部分AMS.handleAppCrashLocked的主要功能:

  1. 当同一进程1分钟之内连续两次crash,则执行的情况下:
    • 对于非persistent进程:
      • ASS.handleAppCrashLocked, 直接结束该应用所有activity
      • AMS.removeProcessLocked,杀死该进程以及同一个进程组下的所有进
      • ASS.resumeTopActivitiesLocked,恢复栈顶第一个非finishing状态的activity
    • 对于persistent进程,则只执行
      • ASS.resumeTopActivitiesLocked,恢复栈顶第一个非finishing状态的activity
  2. 否则,当进程没连续频繁crash
    • ASS.finishTopRunningActivityLocked,执行结束栈顶正在运行activity

另外,AMS.handleAppCrashLocked,该方法内部主要调用链,如下:

AMS.handleAppCrashLocked
   ASS.handleAppCrashLocked
       AS.handleAppCrashLocked
           AS.finishCurrentActivityLocked
   AMS.removeProcessLocked
       ProcessRecord.kill
       AMS.handleAppDiedLocked
           ASS.handleAppDiedLocked
               AMS.cleanUpApplicationRecordLocked
               AS.handleAppDiedLocked
                   AS.removeHistoryRecordsForAppLocked

   ASS.resumeTopActivitiesLocked
       AS.resumeTopActivityLocked
           AS.resumeTopActivityInnerLocked
   ASS.finishTopRunningActivityLocked
       AS.finishTopRunningActivityLocked
           AS.finishActivityLocked

三、Binder死亡通知

进程被杀,如果还记得Binder的死亡回调机制,在应用进程创建的过程中有一个attachApplicationLocked方法的过程中便会创建死亡通知。

[-> ActivityManagerService.java]

private final boolean attachApplicationLocked(IApplicationThread thread,
            int pid) {
    try {
        //创建binder死亡通知
        AppDeathRecipient adr = new AppDeathRecipient(
                app, pid, thread);
        thread.asBinder().linkToDeath(adr, 0);
        app.deathRecipient = adr;
    } catch (RemoteException e) {
        app.resetPackageList(mProcessStats);
        startProcessLocked(app, "link fail", processName);
        return false;
    }
    ...
}

当binder服务端挂了之后,便会通过binder的DeathRecipient来通知AMS进行相应的清理收尾工作。前面已经降到crash的进程会被kill掉,那么当该进程会杀,则会回调到binderDied()方法。

1. binderDied

[-> ActivityManagerService.java]

private final class AppDeathRecipient implements IBinder.DeathRecipient {
    public void binderDied() {
        synchronized(ActivityManagerService.this) {
            appDiedLocked(mApp, mPid, mAppThread, true);//【见小节2】
        }
    }
}

2. appDiedLocked

final void appDiedLocked(ProcessRecord app, int pid, IApplicationThread thread,
        boolean fromBinderDied) {
    ...
    if (!app.killed) {
        if (!fromBinderDied) {
            Process.killProcessQuiet(pid);
        }
        killProcessGroup(app.info.uid, pid);
        app.killed = true;
    }

    // Clean up already done if the process has been re-started.
    if (app.pid == pid && app.thread != null &&
            app.thread.asBinder() == thread.asBinder()) {
        boolean doLowMem = app.instrumentationClass == null;
        boolean doOomAdj = doLowMem;
        if (!app.killedByAm) {
            mAllowLowerMemLevel = true;
        } else {
            mAllowLowerMemLevel = false;
            doLowMem = false;
        }
        //【见小节3】
        handleAppDiedLocked(app, false, true);

        if (doOomAdj) {
            updateOomAdjLocked();
        }
        if (doLowMem) {
            doLowMemReportIfNeededLocked(app);
        }
    }
    ...
}

3 handleAppDiedLocked

[-> ActivityManagerService.java]

private final void handleAppDiedLocked(ProcessRecord app,
        boolean restarting, boolean allowRestart) {
    int pid = app.pid;
    //清理应用程序service, BroadcastReceiver, ContentProvider相关信息【见小节4】
    boolean kept = cleanUpApplicationRecordLocked(app, restarting, allowRestart, -1);

    if (!kept && !restarting) {
        removeLruProcessLocked(app);
        if (pid > 0) {
            ProcessList.remove(pid);
        }
    }

    //清理activity相关信息
    boolean hasVisibleActivities = mStackSupervisor.handleAppDiedLocked(app);
    app.activities.clear();
    ...
    //恢复栈顶第一个非finish的activity
    if (!restarting && hasVisibleActivities && !mStackSupervisor.resumeTopActivitiesLocked()) {
       mStackSupervisor.ensureActivitiesVisibleLocked(null, 0);
   }
}

4 cleanUpApplicationRecordLocked

该方法清理应用程序service, BroadcastReceiver, ContentProvider,process相关信息,为了便于说明将该方法划分为4个部分讲解

4.1 清理service

参数restarting = false, allowRestart =true, index =-1

private final boolean cleanUpApplicationRecordLocked(ProcessRecord app,
        boolean restarting, boolean allowRestart, int index) {
    ...
    mProcessesToGc.remove(app);
    mPendingPssProcesses.remove(app);

    //如果存在,则清除crash/anr/wait对话框
    if (app.crashDialog != null && !app.forceCrashReport) {
        app.crashDialog.dismiss();
        app.crashDialog = null;
    }
    if (app.anrDialog != null) {
        app.anrDialog.dismiss();
        app.anrDialog = null;
    }
    if (app.waitDialog != null) {
        app.waitDialog.dismiss();
        app.waitDialog = null;
    }

    app.crashing = false;
    app.notResponding = false;

    app.resetPackageList(mProcessStats);
    app.unlinkDeathRecipient(); //解除app的死亡通告
    app.makeInactive(mProcessStats);
    app.waitingToKill = null;
    app.forcingToForeground = null;
    //将app移除前台进程
    updateProcessForegroundLocked(app, false, false);
    app.foregroundActivities = false;
    app.hasShownUi = false;
    app.treatLikeActivity = false;
    app.hasAboveClient = false;
    app.hasClientActivities = false;
    //清理service信息,这个过程也比较复杂,后续再展开
    mServices.killServicesLocked(app, allowRestart);
    boolean restart = false;
}
  • mProcessesToGc:记录着需要尽快执行gc的进程列表
  • mPendingPssProcesses:记录着需要收集内存信息的进程列表

4.2 清理ContentProvider

private final boolean cleanUpApplicationRecordLocked(...) {
    ...
    for (int i = app.pubProviders.size() - 1; i >= 0; i--) {
        //获取该进程已发表的ContentProvider
        ContentProviderRecord cpr = app.pubProviders.valueAt(i);
        final boolean always = app.bad || !allowRestart;
        //ContentProvider服务端被杀,则client端进程也会被杀
        boolean inLaunching = removeDyingProviderLocked(app, cpr, always);
        if ((inLaunching || always) && cpr.hasConnectionOrHandle()) {
            restart = true; //需要重启
        }

        cpr.provider = null;
        cpr.proc = null;
    }
    app.pubProviders.clear();

    //处理正在启动并且是有client端正在等待的ContentProvider
    if (cleanupAppInLaunchingProvidersLocked(app, false)) {
        restart = true;
    }

    //取消已连接的ContentProvider的注册
    if (!app.conProviders.isEmpty()) {
        for (int i = app.conProviders.size() - 1; i >= 0; i--) {
            ContentProviderConnection conn = app.conProviders.get(i);
            conn.provider.connections.remove(conn);

            stopAssociationLocked(app.uid, app.processName, conn.provider.uid,
                    conn.provider.name);
        }
        app.conProviders.clear();
    }

4.3 清理BroadcastReceiver

private final boolean cleanUpApplicationRecordLocked(...) {
    ...
    skipCurrentReceiverLocked(app);

    // 取消注册的广播接收者
    for (int i = app.receivers.size() - 1; i >= 0; i--) {
        removeReceiverLocked(app.receivers.valueAt(i));
    }
    app.receivers.clear();
}

4.4 清理Process

private final boolean cleanUpApplicationRecordLocked(...) {
    ...
    //当app正在备份时的处理方式
    if (mBackupTarget != null && app.pid == mBackupTarget.app.pid) {
        ...
        IBackupManager bm = IBackupManager.Stub.asInterface(
                ServiceManager.getService(Context.BACKUP_SERVICE));
        bm.agentDisconnected(app.info.packageName);
    }

    for (int i = mPendingProcessChanges.size() - 1; i >= 0; i--) {
        ProcessChangeItem item = mPendingProcessChanges.get(i);
        if (item.pid == app.pid) {
            mPendingProcessChanges.remove(i);
            mAvailProcessChanges.add(item);
        }
    }
    mUiHandler.obtainMessage(DISPATCH_PROCESS_DIED, app.pid, app.info.uid, null).sendToTarget();

    if (!app.persistent || app.isolated) {
        removeProcessNameLocked(app.processName, app.uid);
        if (mHeavyWeightProcess == app) {
            mHandler.sendMessage(mHandler.obtainMessage(CANCEL_HEAVY_NOTIFICATION_MSG,
                    mHeavyWeightProcess.userId, 0));
            mHeavyWeightProcess = null;
        }
    } else if (!app.removed) {
        //对于persistent应用,则需要重启
        if (mPersistentStartingProcesses.indexOf(app) < 0) {
            mPersistentStartingProcesses.add(app);
            restart = true;
        }
    }

    //mProcessesOnHold:记录着试图在系统ready之前就启动的进程。
    //在那时并不启动这些进程,先记录下来,等系统启动完成则启动这些进程。
    mProcessesOnHold.remove(app);

    if (app == mHomeProcess) {
        mHomeProcess = null;
    }
    if (app == mPreviousProcess) {
        mPreviousProcess = null;
    }

    if (restart && !app.isolated) {
        //仍有组件需要运行在该进程中,因此重启该进程
        if (index < 0) {
            ProcessList.remove(app.pid);
        }
        addProcessNameLocked(app);
        startProcessLocked(app, "restart", app.processName);
        return true;
    } else if (app.pid > 0 && app.pid != MY_PID) {
        //移除该进程相关信息
        boolean removed;
        synchronized (mPidsSelfLocked) {
            mPidsSelfLocked.remove(app.pid);
            mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
        }
        app.setPid(0);
    }
    return false;
}

对于需要重启进程的情形有:

  • mLaunchingProviders:记录着存在client端等待的ContentProvider。应用当前正在启动中,当ContentProvider一旦发布则将该ContentProvider将从该list去除。当进程包含这样的ContentProvider,则需要重启进程。
  • mPersistentStartingProcesses:记录着试图在系统ready之前就启动的进程。在那时并不启动这些进程,先记录下来,等系统启动完成则启动这些进程。当进程属于这种类型也需要重启。

5. 小结

当crash进程执行kill操作后,进程被杀。此时需要掌握binder 死亡通知原理,由于Crash进程中拥有一个Binder服务端ApplicationThread,而应用进程在创建过程调用attachApplicationLocked(),从而attach到system_server进程,在system_server进程内有一个ApplicationThreadProxy,这是相对应的Binder客户端。当Binder服务端ApplicationThread所在进程(即Crash进程)挂掉后,则Binder客户端能收到相应的死亡通知,从而进入binderDied流程。更多关于bInder原理,这里就不细说,博客中有关于binder系列的专题。

binder_died

四、 总结

本文主要以源码的视角,详细介绍了到应用crash后系统的处理流程:

  1. 首先发生crash所在进程,在创建之初便准备好了defaultUncaughtHandler,用来来处理Uncaught Exception,并输出当前crash基本信息;
  2. 调用当前进程中的AMP.handleApplicationCrash;经过binder ipc机制,传递到system_server进程;
  3. 接下来,进入system_server进程,调用binder服务端执行AMS.handleApplicationCrash;
  4. mProcessNames查找到目标进程的ProcessRecord对象;并将进程crash信息输出到目录/data/system/dropbox
  5. 执行makeAppCrashingLocked
    • 创建当前用户下的crash应用的error receiver,并忽略当前应用的广播;
    • 停止当前进程中所有activity中的WMS的冻结屏幕消息,并执行相关一些屏幕相关操作;
  6. 再执行handleAppCrashLocked方法,
    • 当1分钟内同一进程连续crash两次时,且非persistent进程,则直接结束该应用所有activity,并杀死该进程以及同一个进程组下的所有进程。然后再恢复栈顶第一个非finishing状态的activity;
    • 当1分钟内同一进程连续crash两次时,且persistent进程,,则只执行恢复栈顶第一个非finishing状态的activity;
    • 当1分钟内同一进程未发生连续crash两次时,则执行结束栈顶正在运行activity的流程。
  7. 通过mUiHandler发送消息SHOW_ERROR_MSG,弹出crash对话框;
  8. 到此,system_server进程执行完成。回到crash进程开始执行杀掉当前进程的操作;
  9. 当crash进程被杀,通过binder死亡通知,告知system_server进程来执行appDiedLocked();
  10. 最后,执行清理应用相关的activity/service/ContentProvider/receiver组件信息。

这基本就是整个应用Crash后系统的执行过程。


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