为什么会触发ANR，从源码中扒一扒

private final void realStartServiceLocked(ServiceRecord r, ProcessRecord app, boolean execInFg) throws RemoteException {
    ...
    //发送delay消息(SERVICE_TIMEOUT_MSG)，
    bumpServiceExecutingLocked(r, execInFg, "create");
    try {
        ...
        //最终执行服务的onCreate()方法
        app.thread.scheduleCreateService(r, r.serviceInfo,
                mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
                app.repProcState);
    } catch (DeadObjectException e) {
        mAm.appDiedLocked(app);
        throw e;
    } finally {
        ...
    }
}
private final void bumpServiceExecutingLocked(ServiceRecord r, boolean fg, String why) {
    ... 
    scheduleServiceTimeoutLocked(r.app);
}
void scheduleServiceTimeoutLocked(ProcessRecord proc) {
    if (proc.executingServices.size() == 0 || proc.thread == null) {
        return;
    }
    long now = SystemClock.uptimeMillis();
    Message msg = mAm.mHandler.obtainMessage(
            ActivityManagerService.SERVICE_TIMEOUT_MSG);
    msg.obj = proc;
    //当超时后仍没有remove该SERVICE_TIMEOUT_MSG消息，则执行service Timeout流程
    mAm.mHandler.sendMessageAtTime(msg,
        proc.execServicesFg ? (now+SERVICE_TIMEOUT) : (now+ SERVICE_BACKGROUND_TIMEOUT));
}

private void serviceDoneExecutingLocked(ServiceRecord r, boolean inDestroying, boolean finishing) {
    ...
    if (r.executeNesting <= 0) {
        if (r.app != null) {
            r.app.execServicesFg = false;
            r.app.executingServices.remove(r);
            if (r.app.executingServices.size() == 0) {
                //当前服务所在进程中没有正在执行的service
                mAm.mHandler.removeMessages(ActivityManagerService.SERVICE_TIMEOUT_MSG, r.app);
        ...
    }
    ...

void serviceTimeout(ProcessRecord proc) {
    String anrMessage = null;
    synchronized(mAm) {
        if (proc.executingServices.size() == 0 || proc.thread == null) {
            return;
        }
        final long now = SystemClock.uptimeMillis();
        final long maxTime =  now -
                (proc.execServicesFg ? SERVICE_TIMEOUT : SERVICE_BACKGROUND_TIMEOUT);
        ServiceRecord timeout = null;
        long nextTime = 0;
        for (int i=proc.executingServices.size()-1; i>=0; i--) {
            ServiceRecord sr = proc.executingServices.valueAt(i);
            if (sr.executingStart < maxTime) {
                timeout = sr;
                break;
            }
            if (sr.executingStart > nextTime) {
                nextTime = sr.executingStart;
            }
        }
        if (timeout != null && mAm.mLruProcesses.contains(proc)) {
            Slog.w(TAG, "Timeout executing service: " + timeout);
            StringWriter sw = new StringWriter();
            PrintWriter pw = new FastPrintWriter(sw, false, 1024);
            pw.println(timeout);
            timeout.dump(pw, " ");
            pw.close();
            mLastAnrDump = sw.toString();
            mAm.mHandler.removeCallbacks(mLastAnrDumpClearer);
            mAm.mHandler.postDelayed(mLastAnrDumpClearer, LAST_ANR_LIFETIME_DURATION_MSECS);
            anrMessage = "executing service " + timeout.shortName;
        }
    }
    if (anrMessage != null) {
        //当存在timeout的service，则执行appNotResponding
        mAm.appNotResponding(proc, null, null, false, anrMessage);
    }
}

final void processNextBroadcast(boolean fromMsg) {
    synchronized(mService) {
        ...
        //part 2: 处理当前有序广播
        do {
            r = mOrderedBroadcasts.get(0);
            //获取所有该广播所有的接收者
            int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
            if (mService.mProcessesReady && r.dispatchTime > 0) {
                long now = SystemClock.uptimeMillis();
                if ((numReceivers > 0) &&
                        (now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {
                    //当广播处理时间超时，则强制结束这条广播
                    broadcastTimeoutLocked(false);
                    ...
                }
            }
            if (r.receivers == null || r.nextReceiver >= numReceivers
                    || r.resultAbort || forceReceive) {
                if (r.resultTo != null) {
                    //处理广播消息消息
                    performReceiveLocked(r.callerApp, r.resultTo,
                        new Intent(r.intent), r.resultCode,
                        r.resultData, r.resultExtras, false, false, r.userId);
                    r.resultTo = null;
                }
                //拆炸弹
                cancelBroadcastTimeoutLocked();
            }
        } while (r == null);
        ...
        //part 3: 获取下条有序广播
        r.receiverTime = SystemClock.uptimeMillis();
        if (!mPendingBroadcastTimeoutMessage) {
            long timeoutTime = r.receiverTime + mTimeoutPeriod;
            //埋炸弹
            setBroadcastTimeoutLocked(timeoutTime);
        }
        ...
    }
}

final void setBroadcastTimeoutLocked(long timeoutTime) {
    if (! mPendingBroadcastTimeoutMessage) {
        Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
        mHandler.sendMessageAtTime(msg, timeoutTime);
        mPendingBroadcastTimeoutMessage = true;
    }
}

final void cancelBroadcastTimeoutLocked() {
    if (mPendingBroadcastTimeoutMessage) {
        mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);
        mPendingBroadcastTimeoutMessage = false;
    }
}