Android弹出异常dialog源码分析

我们从RuntimeInit.java这个类开始分析;

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!");
    }

再看看 commonInit()这个方法:

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.
         */
        Thread.setUncaughtExceptionPreHandler(new LoggingHandler());
        Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler());

        /*
         * Install a TimezoneGetter subclass for ZoneInfo.db
         */
        TimezoneGetter.setInstance(new TimezoneGetter() {
            @Override
            public String getId() {
                return SystemProperties.get("persist.sys.timezone");
            }
        });
        TimeZone.setDefault(null);

        /*
         * Sets handler for java.util.logging to use Android log facilities.
         * The odd "new instance-and-then-throw-away" is a mirror of how
         * the "java.util.logging.config.class" system property works. We
         * can't use the system property here since the logger has almost
         * certainly already been initialized.
         */
        LogManager.getLogManager().reset();
        new AndroidConfig();

        /*
         * Sets the default HTTP User-Agent used by HttpURLConnection.
         */
        String userAgent = getDefaultUserAgent();
        System.setProperty("http.agent", userAgent);

        /*
         * Wire socket tagging to traffic stats.
         */
        NetworkManagementSocketTagger.install();

        /*
         * If we're running in an emulator launched with "-trace", put the
         * VM into emulator trace profiling mode so that the user can hit
         * F9/F10 at any time to capture traces.  This has performance
         * consequences, so it's not something you want to do always.
         */
        String trace = SystemProperties.get("ro.kernel.android.tracing");
        if (trace.equals("1")) {
            Slog.i(TAG, "NOTE: emulator trace profiling enabled");
            Debug.enableEmulatorTraceOutput();
        }

        initialized = true;
    }

注意里面有个Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler());表示当我们对异常不处理时候,Android系统会提供给我们一个默认的异常处理方式,那么google会怎么处理呢,再继续往下看.

 private static class KillApplicationHandler implements Thread.UncaughtExceptionHandler {
        public void uncaughtException(Thread t, Throwable e) {
            try {
                // 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);
            }
        }
    }

这里我们着重看下 ActivityManager.getService().handleApplicationCrash(
mApplicationObject, new ApplicationErrorReport.ParcelableCrashInfo(e));这行代码,默认的处理逻辑交给了AMS的handleApplicationCrash()方法,那么我们继续往下看AMS的这个方法.

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);
    }

继续看handleApplicationCrashInner()这个方法

 void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
            ApplicationErrorReport.CrashInfo crashInfo) {
        EventLog.writeEvent(EventLogTags.AM_CRASH, Binder.getCallingPid(),
                UserHandle.getUserId(Binder.getCallingUid()), processName,
                r == null ? -1 : r.info.flags,
                crashInfo.exceptionClassName,
                crashInfo.exceptionMessage,
                crashInfo.throwFileName,
                crashInfo.throwLineNumber);

        addErrorToDropBox(eventType, r, processName, null, null, null, null, null, crashInfo);

        mAppErrors.crashApplication(r, crashInfo);
    }

这里出现了一个 mAppErrors.crashApplication(r, crashInfo);这是个什么玩意儿呢,Android默认处理异常时把app杀掉,那么这个杀掉app的任务交给了mAppErrors这个对象,这个对象是AppErrors.java这个类,抽一下这个类是干啥的.

/**
 * Controls error conditions in applications.
 */
class AppErrors {

    private static final String TAG = TAG_WITH_CLASS_NAME ? "AppErrors" : TAG_AM;

    private final ActivityManagerService mService;
    private final Context mContext;

    private ArraySet mAppsNotReportingCrashes;

通过注释我们可以猜测这个类是处理app异常逻辑的控制中心,好了废话不多说,继续追踪源码.

  /**
     * Bring up the "unexpected error" dialog box for a crashing app.
     * Deal with edge cases (intercepts from instrumented applications,
     * ActivityController, error intent receivers, that sort of thing).
     * @param r the application crashing
     * @param crashInfo describing the failure
     */
    void crashApplication(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo) {
        final int callingPid = Binder.getCallingPid();
        final int callingUid = Binder.getCallingUid();

        final long origId = Binder.clearCallingIdentity();
        try {
            crashApplicationInner(r, crashInfo, callingPid, callingUid);
        } finally {
            Binder.restoreCallingIdentity(origId);
        }
    }

这里追踪到了crashApplicationInner()这个方法,继续看,这个方法老长了,我只是先截取其中一段主要代码看,

 AppErrorResult result = new AppErrorResult();
        TaskRecord task;
        synchronized (mService) {
            /**
             * If crash is handled by instance of {@link android.app.IActivityController},
             * finish now and don't show the app error dialog.
             */
            if (handleAppCrashInActivityController(r, crashInfo, shortMsg, longMsg, stackTrace,
                    timeMillis, callingPid, callingUid)) {
                return;
            }

            /**
             * If this process was running instrumentation, finish now - it will be handled in
             * {@link ActivityManagerService#handleAppDiedLocked}.
             */
            if (r != null && r.instr != null) {
                return;
            }

            // Log crash in battery stats.
            if (r != null) {
                mService.mBatteryStatsService.noteProcessCrash(r.processName, r.uid);
            }

            AppErrorDialog.Data data = new AppErrorDialog.Data();
            data.result = result;
            data.proc = r;

            // If we can't identify the process or it's already exceeded its crash quota,
            // quit right away without showing a crash dialog.
            if (r == null || !makeAppCrashingLocked(r, shortMsg, longMsg, stackTrace, data)) {
                return;
            }

            final Message msg = Message.obtain();
            msg.what = ActivityManagerService.SHOW_ERROR_UI_MSG;

            task = data.task;
            msg.obj = data;
            mService.mUiHandler.sendMessage(msg);

我们看到这个方法里开始构造了一个AppErrorDialog.Data对象,然后利用handler将这个对象send出去,那么send到什么地方去了呢,可以看到mService.mUiHandler.sendMessage(msg);那么mUiHandler到底是个啥呢?点进去看下,mUiHandler是AMS内部一个成员变量,UiHandler extends Handler.

 final class UiHandler extends Handler {
        public UiHandler() {
            super(com.android.server.UiThread.get().getLooper(), null, true);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case SHOW_ERROR_UI_MSG: {
                mAppErrors.handleShowAppErrorUi(msg);
                ensureBootCompleted();
            } break;
            case SHOW_NOT_RESPONDING_UI_MSG: {
                mAppErrors.handleShowAnrUi(msg);
                ensureBootCompleted();
            } break;
            case SHOW_STRICT_MODE_VIOLATION_UI_MSG: {
                HashMap data = (HashMap) msg.obj;
                synchronized (ActivityManagerService.this) {
                    ProcessRecord proc = (ProcessRecord) data.get("app");
                    if (proc == null) {
                        Slog.e(TAG, "App not found when showing strict mode dialog.");
                        break;
                    }
                    if (proc.crashDialog != null) {
                        Slog.e(TAG, "App already has strict mode dialog: " + proc);
                        return;
                    }
                    AppErrorResult res = (AppErrorResult) data.get("result");
                    if (mShowDialogs && !mSleeping && !mShuttingDown) {
                        Dialog d = new StrictModeViolationDialog(mUiContext,
                                ActivityManagerService.this, res, proc);
                        d.show();
                        proc.crashDialog = d;
                    } else {
                        // The device is asleep, so just pretend that the user
                        // saw a crash dialog and hit "force quit".
                        res.set(0);
                    }
                }
                ensureBootCompleted();
            } break;
            case SHOW_FACTORY_ERROR_UI_MSG: {
                Dialog d = new FactoryErrorDialog(
                        mUiContext, msg.getData().getCharSequence("msg"));
                d.show();
                ensureBootCompleted();
            } break;

我们上面msg.what = ActivityManagerService.SHOW_ERROR_UI_MSG,那么UIHandler的handMessage里对应的这个case就是第一个, 走到了mAppErrors.handleShowAppErrorUi(msg)这里;我们继续看下AppErrors类的handleShowAppErrorUi方法做了什么.

 void handleShowAppErrorUi(Message msg) {
        AppErrorDialog.Data data = (AppErrorDialog.Data) msg.obj;
        boolean showBackground = Settings.Secure.getInt(mContext.getContentResolver(),
                Settings.Secure.ANR_SHOW_BACKGROUND, 0) != 0;
        synchronized (mService) {
            ProcessRecord proc = data.proc;
            AppErrorResult res = data.result;
            if (proc != null && proc.crashDialog != null) {
                Slog.e(TAG, "App already has crash dialog: " + proc);
                if (res != null) {
                    res.set(AppErrorDialog.ALREADY_SHOWING);
                }
                return;
            }
            boolean isBackground = (UserHandle.getAppId(proc.uid)
                    >= Process.FIRST_APPLICATION_UID
                    && proc.pid != MY_PID);
            for (int userId : mService.mUserController.getCurrentProfileIdsLocked()) {
                isBackground &= (proc.userId != userId);
            }
            if (isBackground && !showBackground) {
                Slog.w(TAG, "Skipping crash dialog of " + proc + ": background");
                if (res != null) {
                    res.set(AppErrorDialog.BACKGROUND_USER);
                }
                return;
            }
            final boolean crashSilenced = mAppsNotReportingCrashes != null &&
                    mAppsNotReportingCrashes.contains(proc.info.packageName);
            if ((mService.canShowErrorDialogs() || showBackground) && !crashSilenced) {
                proc.crashDialog = new AppErrorDialog(mContext, mService, data);
            } else {
                // The device is asleep, so just pretend that the user
                // saw a crash dialog and hit "force quit".
                if (res != null) {
                    res.set(AppErrorDialog.CANT_SHOW);
                }
            }
        }
        // If we've created a crash dialog, show it without the lock held
        if(data.proc.crashDialog != null) {
            Slog.i(TAG, "Showing crash dialog for package " + data.proc.info.packageName
                    + " u" + data.proc.userId);
            data.proc.crashDialog.show();
        }
    }

这里可以看到全部是对AppErrorDialog.Data的成员变量AppErrorResult进行赋值操作,那么赋完值要干啥呢, proc.crashDialog = new AppErrorDialog(mContext, mService, data);这行代码就是创造一个CarshDialog,然后 data.proc.crashDialog.show();那么现在流程清晰了,Android系统对异常默认处理弹出dialog流程到这里基本清晰了,最后我们再看下AppErrorDialog,

final class AppErrorDialog extends BaseErrorDialog implements View.OnClickListener {

    private final ActivityManagerService mService;
    private final AppErrorResult mResult;
    private final ProcessRecord mProc;
    private final boolean mRepeating;
    private final boolean mIsRestartable;

这个类是继承自BaseErrorDialog,而BaseErrorDialog继承自AlertDialog,这没什么好说的,我们看下dialog中的点击事件有这样一段代码.

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case com.android.internal.R.id.aerr_restart:
                mHandler.obtainMessage(RESTART).sendToTarget();
                break;
            case com.android.internal.R.id.aerr_report:
                mHandler.obtainMessage(FORCE_QUIT_AND_REPORT).sendToTarget();
                break;
            case com.android.internal.R.id.aerr_close:
                mHandler.obtainMessage(FORCE_QUIT).sendToTarget();
                break;
            case com.android.internal.R.id.aerr_mute:
                mHandler.obtainMessage(MUTE).sendToTarget();
                break;
            default:
                break;
        }
    }

可以看到当我们点击取消或者确定按钮以后,会有 mHandler.obtainMessage(RESTART).sendToTarget();或者 mHandler.obtainMessage(FORCE_QUIT).sendToTarget();操作,那么这个msg消息又会如何处理呢,看下

private final Handler mHandler = new Handler() {
        public void handleMessage(Message msg) {
            setResult(msg.what);
            dismiss();
        }
    };

  private void setResult(int result) {
        synchronized (mService) {
            if (mProc != null && mProc.crashDialog == AppErrorDialog.this) {
                mProc.crashDialog = null;
            }
        }
        mResult.set(result);

        // Make sure we don't have time timeout still hanging around.
        mHandler.removeMessages(TIMEOUT);
    }

这里重要的代码就是这行 mResult.set(result);这个mResult就是创建dialog是从前面的AppErrors中传递过来的AppErrorResult,看下代码实现

 public AppErrorDialog(Context context, ActivityManagerService service, Data data) {
        super(context);
        Resources res = context.getResources();

        mService = service;
        mProc = data.proc;
        mResult = data.result;
        mRepeating = data.repeating;
        mIsRestartable = data.task != null || data.isRestartableForService;
        BidiFormatter bidi = BidiFormatter.getInstance();

那么现在对这个AppErrorResult重新赋值意义何在呢,还记得AppErrors中的crashApplicationInner这个方法吗?很长,当时只是截取其中一段代码,那么我们现在时候看下下半部分的代码了.

  int res = result.get();

        Intent appErrorIntent = null;
        MetricsLogger.action(mContext, MetricsProto.MetricsEvent.ACTION_APP_CRASH, res);
        if (res == AppErrorDialog.TIMEOUT || res == AppErrorDialog.CANCEL) {
            res = AppErrorDialog.FORCE_QUIT;
        }
        synchronized (mService) {
            if (res == AppErrorDialog.MUTE) {
                stopReportingCrashesLocked(r);
            }
            if (res == AppErrorDialog.RESTART) {
                mService.removeProcessLocked(r, false, true, "crash");
                if (task != null) {
                    try {
                        mService.startActivityFromRecents(task.taskId,
                                ActivityOptions.makeBasic().toBundle());
                    } catch (IllegalArgumentException e) {
                        // Hmm, that didn't work, app might have crashed before creating a
                        // recents entry. Let's see if we have a safe-to-restart intent.
                        final Set cats = task.intent.getCategories();
                        if (cats != null && cats.contains(Intent.CATEGORY_LAUNCHER)) {
                            mService.startActivityInPackage(task.mCallingUid,
                                    task.mCallingPackage, task.intent,
                                    null, null, null, 0, 0,
                                    ActivityOptions.makeBasic().toBundle(),
                                    task.userId, null, null, "AppErrors");
                        }
                    }
                }
            }
            if (res == AppErrorDialog.FORCE_QUIT) {
                long orig = Binder.clearCallingIdentity();
                try {
                    // Kill it with fire!
                    mService.mStackSupervisor.handleAppCrashLocked(r);
                    if (!r.persistent) {
                        mService.removeProcessLocked(r, false, false, "crash");
                        mService.mStackSupervisor.resumeFocusedStackTopActivityLocked();
                    }
                } finally {
                    Binder.restoreCallingIdentity(orig);
                }
            }
            if (res == AppErrorDialog.FORCE_QUIT_AND_REPORT) {
                appErrorIntent = createAppErrorIntentLocked(r, timeMillis, crashInfo);
            }
            if (r != null && !r.isolated && res != AppErrorDialog.RESTART) {
                // XXX Can't keep track of crash time for isolated processes,
                // since they don't have a persistent identity.
                mProcessCrashTimes.put(r.info.processName, r.uid,
                        SystemClock.uptimeMillis());
            }
        }

这里我们可以看到关于res的判断,而这个res就是AppErrorResult对象,此时我们已经在AppErrorDialog中完成了AppErrorResult这个对象的赋值操作,这里就会对Activity进行重启或者杀死操作.

至此,Android弹出异常对话框的源码就分析完了,更深层次的分析还需要深入到底层代码实现,这里只是浅析了FrameWork层的异常处理代码