廣播在android系統中，使用非常頻繁，可以說是耦合度極低的一種通訊方式。作業系統一方面為了讓任務執行互不干擾，即使某個任務掛了，也不會影響其他的任務，因此才有了程序，但是任務之間通常又是相關的，又需要涉及到程序間的通訊，當然程序間通訊的方式有很多種，管道、訊號、訊息佇列、共享記憶體等，socket也算是一種，android採用的是Binder，但是我們應用層開發的時候，基本上沒有讓我們直接操作Binder，也就是直接參與到程序間的通訊細節，這樣會給我們一種錯覺，程序好像是一體的，通訊很簡單，android系統一方面將不同的任務放在不同的程序中，一方面又模糊程序的概念，讓它看起來就是一個整體，確實相當了不起。廢話不多說，直接看分析。 一、廣播的註冊過程

四大元件中，廣播是唯一一個可以不需要在AndroidMenifest.xml中註冊的元件，根據是否在AndroidMenifest.xml註冊，分為靜態廣播和動態廣播，此外還分為前臺廣播和後臺廣播，也分為有序廣播和無序廣播，分類挺多的，四大元件如果是在AndroidMenifest.xml註冊的，註冊過程由PMS來負責，我們這邊只管動態廣播，也就是在程式碼中註冊的。先來看一個簡單的廣播註冊例子：

//new出上邊定義好的BroadcastReceiver
MyBroadCastReceiver smsBroadCastReceiver = new MyBroadCastReceiver();

//例項化過濾器並設定要過濾的廣播  
IntentFilter intentFilter = new IntentFilter("android.provider.Telephony.SMS_RECEIVED");

//註冊廣播   
mContext.registerReceiver(smsBroadCastReceiver,intentFilter);
 

一個廣播接收器，和一個過濾器，重點不是這個，主要講register的過程，在Service的啟動流程中，我們已經知道mContext就是ContextImpl，這裡同樣是這個類，從Activity和Service的啟動流程應該已經看出來，基本都是套路了，涉及到程序間通訊的，先轉化為實現IBinder的物件，然後扔給AMS呼叫，接著再扔給某個對應的類來專門處理。廣播的註冊過程除了最後一個不滿足(傳送和接收是滿足的)，其實也是這個套路。先貼出幾個呼叫的介面，最後都呼叫到了registerReceiverInternal裡面。

@Override
    public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
        return registerReceiver(receiver, filter, null, null);
    }

    @Override
    public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter,
            String broadcastPermission, Handler scheduler) {
        return registerReceiverInternal(receiver, getUserId(),
                filter, broadcastPermission, scheduler, getOuterContext());
    }

    @Override
    public Intent registerReceiverAsUser(BroadcastReceiver receiver, UserHandle user,
            IntentFilter filter, String broadcastPermission, Handler scheduler) {
        return registerReceiverInternal(receiver, user.getIdentifier(),
                filter, broadcastPermission, scheduler, getOuterContext());
    }
 

再來看看這個方法的內容，由於廣播涉及到程序間通訊，它首先會講receiver通過LoadedApk來轉化為實現了IBinder介面的物件IIntentReceiver，再扔給AMS處理。

    private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
            IntentFilter filter, String broadcastPermission,
            Handler scheduler, Context context) {
        IIntentReceiver rd = null;
        if (receiver != null) {
            if (mPackageInfo != null && context != null) {
                if (scheduler == null) {
                    scheduler = mMainThread.getHandler();
                }
                rd = mPackageInfo.getReceiverDispatcher(
                    receiver, context, scheduler,
                    mMainThread.getInstrumentation(), true);
            } else {
                if (scheduler == null) {
                    scheduler = mMainThread.getHandler();
                }
                rd = new LoadedApk.ReceiverDispatcher(
                        receiver, context, scheduler, null, true).getIIntentReceiver();
            }
        }
        try {
            return ActivityManagerNative.getDefault().registerReceiver(
                    mMainThread.getApplicationThread(), mBasePackageName,
                    rd, filter, broadcastPermission, userId);
        } catch (RemoteException e) {
            return null;
        }
    }
 

可以關注下面這個程式碼，mPackageInfo是LoadedApk這個類的物件，具體程式碼是什麼，感興趣的可以自己看一下原始碼

    rd = mPackageInfo.getReceiverDispatcher(
                    receiver, context, scheduler,
                    mMainThread.getInstrumentation(), true);

至於IIntentReceiver，它是在AIDL中寫的，android編譯的時候會把它先生成對應的類，可以看到只有一個performReceive介面，不多說，繼續往下。

oneway interface IIntentReceiver {
    void performReceive(in Intent intent, int resultCode, String data,
            in Bundle extras, boolean ordered, boolean sticky, int sendingUser);
}

最後廣播的註冊過程都是呼叫到AMS的registerReceiver方法中，下面是方法的關鍵部分，最終receiver和intentfilter都被儲存了起來。

   public Intent registerReceiver(IApplicationThread caller, String callerPackage,
            IIntentReceiver receiver, IntentFilter filter, String permission, int userId) {
        ......

        synchronized (this) {
            if (callerApp != null && (callerApp.thread == null
                    || callerApp.thread.asBinder() != caller.asBinder())) {
                // Original caller already died
                return null;
            }
            ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
            if (rl == null) {
                rl = new ReceiverList(this, callerApp, callingPid, callingUid,
                        userId, receiver);
                if (rl.app != null) {
                    rl.app.receivers.add(rl);
                } else {
                    try {
                        receiver.asBinder().linkToDeath(rl, 0);
                    } catch (RemoteException e) {
                        return sticky;
                    }
                    rl.linkedToDeath = true;
                }
                mRegisteredReceivers.put(receiver.asBinder(), rl);
            } 
            ......
            BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
                    permission, callingUid, userId);
            rl.add(bf);
            if (!bf.debugCheck()) {
                Slog.w(TAG, "==> For Dynamic broadcast");
            }
            mReceiverResolver.addFilter(bf);

            .......
        }
    }

二、廣播的傳送和接收過程 廣播的接收，也是在ContextImpl中呼叫的，也有幾個介面，最後呼叫也是AMS種的同一個方法，我們只看其中一個

   public void sendBroadcast(Intent intent) {
        warnIfCallingFromSystemProcess();
        String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
        try {
            intent.prepareToLeaveProcess();
            ActivityManagerNative.getDefault().broadcastIntent(
                    mMainThread.getApplicationThread(), intent, resolvedType, null,
                    Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, null, false, false,
                    getUserId());
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
    }

然後來看一下AMS中的broadcastIntent方法

    public final int broadcastIntent(IApplicationThread caller,
            Intent intent, String resolvedType, IIntentReceiver resultTo,
            int resultCode, String resultData, Bundle resultExtras,
            String[] requiredPermissions, int appOp, Bundle options,
            boolean serialized, boolean sticky, int userId) {
        enforceNotIsolatedCaller("broadcastIntent");
        synchronized(this) {
            intent = verifyBroadcastLocked(intent);

            final ProcessRecord callerApp = getRecordForAppLocked(caller);
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();
            final long origId = Binder.clearCallingIdentity();
            int res = broadcastIntentLocked(callerApp,
                    callerApp != null ? callerApp.info.packageName : null,
                    intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
                    requiredPermissions, appOp, null, serialized, sticky,
                    callingPid, callingUid, userId);
            Binder.restoreCallingIdentity(origId);
            return res;
        }
    }

實際上，然後它呼叫到了AMS得另一個方法中broadcastIntentLocked去了，方法比較長，只看核心的部分，

   private final int broadcastIntentLocked(ProcessRecord callerApp,
            String callerPackage, Intent intent, String resolvedType,
            IIntentReceiver resultTo, int resultCode, String resultData,
            Bundle resultExtras, String[] requiredPermissions, int appOp, Bundle options,
            boolean ordered, boolean sticky, int callingPid, int callingUid, int userId) {
        .......

        // Figure out who all will receive this broadcast.
        List receivers = null;
        List<BroadcastFilter> registeredReceivers = null;
        // Need to resolve the intent to interested receivers...
        if ((intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY)
                 == 0) {
            receivers = collectReceiverComponents(intent, resolvedType, callingUid, users);
        }
        if (intent.getComponent() == null) {
            if (userId == UserHandle.USER_ALL && callingUid == Process.SHELL_UID) {
                // Query one target user at a time, excluding shell-restricted users
                UserManagerService ums = getUserManagerLocked();
                for (int i = 0; i < users.length; i++) {
                    if (ums.hasUserRestriction(
                            UserManager.DISALLOW_DEBUGGING_FEATURES, users[i])) {
                        continue;
                    }
                    List<BroadcastFilter> registeredReceiversForUser =
                            mReceiverResolver.queryIntent(intent,
                                    resolvedType, false, users[i]);
                    if (registeredReceivers == null) {
                        registeredReceivers = registeredReceiversForUser;
                    } else if (registeredReceiversForUser != null) {
                        registeredReceivers.addAll(registeredReceiversForUser);
                    }
                }
            } else {
                registeredReceivers = mReceiverResolver.queryIntent(intent,
                        resolvedType, false, userId);
            }
        }

        final boolean replacePending =
                (intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;

        if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueing broadcast: " + intent.getAction()
                + " replacePending=" + replacePending);

        int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
        if (!ordered && NR > 0) {
            // If we are not serializing this broadcast, then send the
            // registered receivers separately so they don't wait for the
            // components to be launched.
            final BroadcastQueue queue = broadcastQueueForIntent(intent);
            BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
                    callerPackage, callingPid, callingUid, resolvedType, requiredPermissions,
                    appOp, brOptions, registeredReceivers, resultTo, resultCode, resultData,
                    resultExtras, ordered, sticky, false, userId);
            if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing parallel broadcast " + r);
            final boolean replaced = replacePending && queue.replaceParallelBroadcastLocked(r);
            if (!replaced) {
                queue.enqueueParallelBroadcastLocked(r);
                queue.scheduleBroadcastsLocked();
            }
            registeredReceivers = null;
            NR = 0;
        }

        .....

        if ((receivers != null && receivers.size() > 0)
                || resultTo != null) {
            BroadcastQueue queue = broadcastQueueForIntent(intent);
            BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
                    callerPackage, callingPid, callingUid, resolvedType,
                    requiredPermissions, appOp, brOptions, receivers, resultTo, resultCode,
                    resultData, resultExtras, ordered, sticky, false, userId);

            if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing ordered broadcast " + r
                    + ": prev had " + queue.mOrderedBroadcasts.size());
            if (DEBUG_BROADCAST) Slog.i(TAG_BROADCAST,
                    "Enqueueing broadcast " + r.intent.getAction());

            boolean replaced = replacePending && queue.replaceOrderedBroadcastLocked(r);
            if (!replaced) {
                queue.enqueueOrderedBroadcastLocked(r);
                queue.scheduleBroadcastsLocked();
            }
        }

        return ActivityManager.BROADCAST_SUCCESS;
    }

過程基本上是，根據intent-filter找到廣播接受者，構建BroadcastRecord物件，扔到BroadcastQueue中，由BroadcastQueue負責傳送給對應的接收者，我們來看BroadcastQueue這部分的程式碼。

   public void scheduleBroadcastsLocked() {
        if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Schedule broadcasts ["
                + mQueueName + "]: current="
                + mBroadcastsScheduled);

        if (mBroadcastsScheduled) {
            return;
        }
        mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
        mBroadcastsScheduled = true;
    }

上述程式碼傳送了一個BROADCAST_INTENT_MSG訊息，我們看看這個訊息做了什麼事

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BROADCAST_INTENT_MSG: {
                    if (DEBUG_BROADCAST) Slog.v(
                            TAG_BROADCAST, "Received BROADCAST_INTENT_MSG");
                    processNextBroadcast(true);
                } break;
                case BROADCAST_TIMEOUT_MSG: {
                    synchronized (mService) {
                        broadcastTimeoutLocked(true);
                    }
                } break;
                case SCHEDULE_TEMP_WHITELIST_MSG: {
                    DeviceIdleController.LocalService dic = mService.mLocalDeviceIdleController;
                    if (dic != null) {
                        dic.addPowerSaveTempWhitelistAppDirect(UserHandle.getAppId(msg.arg1),
                                msg.arg2, true, (String)msg.obj);
                    }
                } break;
            }
        }

上面程式碼可以看到，它會呼叫processNextBroadcast方法，從字面上可以知道，處理下一條廣播，看看裡面的內容。

    final void processNextBroadcast(boolean fromMsg) {
        synchronized(mService) {
            BroadcastRecord r;
            ......
            // First, deliver any non-serialized broadcasts right away.
            //這裡處理的是無序廣播，也就是普通廣播
            while (mParallelBroadcasts.size() > 0) {
                r = mParallelBroadcasts.remove(0);
                r.dispatchTime = SystemClock.uptimeMillis();
                r.dispatchClockTime = System.currentTimeMillis();
                final int N = r.receivers.size();
                if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing parallel broadcast ["
                        + mQueueName + "] " + r);
                for (int i=0; i<N; i++) {
                    Object target = r.receivers.get(i);
                    if (DEBUG_BROADCAST)  Slog.v(TAG_BROADCAST,
                            "Delivering non-ordered on [" + mQueueName + "] to registered "
                            + target + ": " + r);
                    deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false);
                }
                addBroadcastToHistoryLocked(r);
                if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Done with parallel broadcast ["
                        + mQueueName + "] " + r);
            }

            // Now take care of the next serialized one...

            ......

            boolean looped = false;
            
            do {
                //這裡處理的是有序廣播
                if (mOrderedBroadcasts.size() == 0) {
                    // No more broadcasts pending, so all done!
                    mService.scheduleAppGcsLocked();
                    if (looped) {
                        // If we had finished the last ordered broadcast, then
                        // make sure all processes have correct oom and sched
                        // adjustments.
                        mService.updateOomAdjLocked();
                    }
                    return;
                }
                r = mOrderedBroadcasts.get(0);
              .....

                if (r.receivers == null || r.nextReceiver >= numReceivers
                        || r.resultAbort || forceReceive) {
                    // No more receivers for this broadcast!  Send the final
                    // result if requested...
                    if (r.resultTo != null) {
                        try {
                            if (DEBUG_BROADCAST) Slog.i(TAG_BROADCAST,
                                    "Finishing broadcast [" + mQueueName + "] "
                                    + r.intent.getAction() + " app=" + r.callerApp);
                            performReceiveLocked(r.callerApp, r.resultTo,
                                new Intent(r.intent), r.resultCode,
                                r.resultData, r.resultExtras, false, false, r.userId);
                            // Set this to null so that the reference
                            // (local and remote) isn't kept in the mBroadcastHistory.
                            r.resultTo = null;
                        } catch (RemoteException e) {
                            r.resultTo = null;
                            Slog.w(TAG, "Failure ["
                                    + mQueueName + "] sending broadcast result of "
                                    + r.intent, e);
                        }
                    }

                    if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Cancelling BROADCAST_TIMEOUT_MSG");
                    cancelBroadcastTimeoutLocked();

                    if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST,
                            "Finished with ordered broadcast " + r);

                    // ... and on to the next...
                    addBroadcastToHistoryLocked(r);
                    mOrderedBroadcasts.remove(0);
                    r = null;
                    looped = true;
                    continue;
                }
            } while (r == null);

            // Get the next receiver...
            int recIdx = r.nextReceiver++;

            // Keep track of when this receiver started, and make sure there
            // is a timeout message pending to kill it if need be.
            r.receiverTime = SystemClock.uptimeMillis();
            if (recIdx == 0) {
                r.dispatchTime = r.receiverTime;
                r.dispatchClockTime = System.currentTimeMillis();
                if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing ordered broadcast ["
                        + mQueueName + "] " + r);
            }
            if (! mPendingBroadcastTimeoutMessage) {
                long timeoutTime = r.receiverTime + mTimeoutPeriod;
                if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
                        "Submitting BROADCAST_TIMEOUT_MSG ["
                        + mQueueName + "] for " + r + " at " + timeoutTime);
                setBroadcastTimeoutLocked(timeoutTime);
            }

           ......
    }

從上面程式碼中可以看到，遍歷mParallelBroadcasts處理無序廣播，遍歷mOrderedBroadcasts處理有序廣播，無序廣播呼叫的介面是deliverToRegisteredReceiverLocked

    private void deliverToRegisteredReceiverLocked(BroadcastRecord r,
            BroadcastFilter filter, boolean ordered) {
            ........
            try {
                if (DEBUG_BROADCAST_LIGHT) Slog.i(TAG_BROADCAST,
                        "Delivering to " + filter + " : " + r);
                performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,
                        new Intent(r.intent), r.resultCode, r.resultData,
                        r.resultExtras, r.ordered, r.initialSticky, r.userId);
                if (ordered) {
                    r.state = BroadcastRecord.CALL_DONE_RECEIVE;
                }
            } catch (RemoteException e) {
                Slog.w(TAG, "Failure sending broadcast " + r.intent, e);
                if (ordered) {
                    r.receiver = null;
                    r.curFilter = null;
                    filter.receiverList.curBroadcast = null;
                    if (filter.receiverList.app != null) {
                        filter.receiverList.app.curReceiver = null;
                    }
                }
            }
        }
    }

然後會呼叫，performReceiveLocked方法

   private static void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
            Intent intent, int resultCode, String data, Bundle extras,
            boolean ordered, boolean sticky, int sendingUser) throws RemoteException {
        // Send the intent to the receiver asynchronously using one-way binder calls.
        if (app != null) {
            if (app.thread != null) {
                // If we have an app thread, do the call through that so it is
                // correctly ordered with other one-way calls.
                app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
                        data, extras, ordered, sticky, sendingUser, app.repProcState);
            } else {
                // Application has died. Receiver doesn't exist.
                throw new RemoteException("app.thread must not be null");
            }
        } else {
            receiver.performReceive(intent, resultCode, data, extras, ordered,
                    sticky, sendingUser);
        }
    }

由於廣播啟動的時候，應用也是啟動了的，然後就會呼叫了app.thread.scheduleRegisteredReceiver，從Activity和Service的啟動流程中都可以看到，這裡是呼叫的ApplicationThread的scheduleRegisteredReceiver方法。

        public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
                int resultCode, String dataStr, Bundle extras, boolean ordered,
                boolean sticky, int sendingUser, int processState) throws RemoteException {
            updateProcessState(processState, false);
            receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
                    sticky, sendingUser);
        }

然後回到了IIntentReceiver的performReceive介面，這個是在LoadedApk.ReceiverDispatcher.InnerReceiver實現這個介面的，我們看看裡面的程式碼

       public void performReceive(Intent intent, int resultCode, String data,
                    Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
                LoadedApk.ReceiverDispatcher rd = mDispatcher.get();
                if (ActivityThread.DEBUG_BROADCAST) {
                    int seq = intent.getIntExtra("seq", -1);
                    Slog.i(ActivityThread.TAG, "Receiving broadcast " + intent.getAction() + " seq=" + seq
                            + " to " + (rd != null ? rd.mReceiver : null));
                }
                if (rd != null) {
                    rd.performReceive(intent, resultCode, data, extras,
                            ordered, sticky, sendingUser);
                } else {
                    // The activity manager dispatched a broadcast to a registered
                    // receiver in this process, but before it could be delivered the
                    // receiver was unregistered.  Acknowledge the broadcast on its
                    // behalf so that the system's broadcast sequence can continue.
                    if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
                            "Finishing broadcast to unregistered receiver");
                    IActivityManager mgr = ActivityManagerNative.getDefault();
                    try {
                        if (extras != null) {
                            extras.setAllowFds(false);
                        }
                        mgr.finishReceiver(this, resultCode, data, extras, false, intent.getFlags());
                    } catch (RemoteException e) {
                        Slog.w(ActivityThread.TAG, "Couldn't finish broadcast to unregistered receiver");
                    }
                }
            }

最後呼叫到的是，LoadedApk.ReceiverDispatcher的performReceive方法

        public void performReceive(Intent intent, int resultCode, String data,
                Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
            if (ActivityThread.DEBUG_BROADCAST) {
                int seq = intent.getIntExtra("seq", -1);
                Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction() + " seq=" + seq
                        + " to " + mReceiver);
            }
            Args args = new Args(intent, resultCode, data, extras, ordered,
                    sticky, sendingUser);
            if (!mActivityThread.post(args)) {
                if (mRegistered && ordered) {
                    IActivityManager mgr = ActivityManagerNative.getDefault();
                    if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
                            "Finishing sync broadcast to " + mReceiver);
                    args.sendFinished(mgr);
                }
            }
        }

然後通過mActivityThread.post(args)方法呼叫，Args是一個Runnable，一下列出其run方法

        public void run() {
                final BroadcastReceiver receiver = mReceiver;
                final boolean ordered = mOrdered;
                ....

                Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveReg");
                try {
                    ClassLoader cl =  mReceiver.getClass().getClassLoader();
                    intent.setExtrasClassLoader(cl);
                    setExtrasClassLoader(cl);
                    receiver.setPendingResult(this);
                    receiver.onReceive(mContext, intent);
                } catch (Exception e) {
                    if (mRegistered && ordered) {
                        if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
                                "Finishing failed broadcast to " + mReceiver);
                        sendFinished(mgr);
                    }
                    if (mInstrumentation == null ||
                            !mInstrumentation.onException(mReceiver, e)) {
                        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                        throw new RuntimeException(
                            "Error receiving broadcast " + intent
                            + " in " + mReceiver, e);
                    }
                }
                
                if (receiver.getPendingResult() != null) {
                    finish();
                }
                Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
            }

這裡最後呼叫了receiver的onReceive方法，以上是無序廣播的呼叫，有序廣播呼叫的是performReceiveLocked，最終和上述流程和無序廣播是相同的。