Android广播发送机制剖析【android广播系列二】

   上篇博客大致说了说广播的注册机制，动态注册和静态注册广播的原理还不1样，动态广播最后HashMap中了，最后放到mReceiverResolver中，
   以后当ActivityManagerService接收到广播的时候，它就能够再成员变量mReceiverResolver中找到对应的广播接收者了。下面我们来讲说广播的发送机制。
   广播发送时候，在Context.java的方法中调用的，有以下方法：
   sendBroadcast(Intent intent) ；
   sendBroadcast(Intent intent, String receiverPermission) 
   sendBroadcastAsUser(Intent intent, UserHandle user) 
   sendBroadcastAsUser(Intent intent, UserHandle user, String receiverPermission)
   sendOrderedBroadcast(Intent intent, String receiverPermission)
   sendOrderedBroadcastAsUser(Intent intent, UserHandle user, String receiverPermission, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
   sendStickyBroadcast(Intent intent) 
   sendStickyBroadcastAsUser(Intent intent, UserHandle user) 
   sendStickyOrderedBroadcast(Intent intent, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
   sendStickyOrderedBroadcastAsUser(Intent intent, UserHandle user, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
  以上就是发送广播的方式，但是经常使用的就几种，其中比较经常使用的就是sendBroadcast(Intent intent) ；我就说下这类发送广播的方式。

发送广播的大致流程

Step1：sendBroadcast（）方法开始

sendBroadcast在context中调用的，往下调用到了ContextImpl.java中去了：

Step2：调用到broadcastIntent（）方法中

调用到了ActivityManagerService.java中的broadcastIntent（）方法中去了，

Step3:调用到broadcastIntentLocked（）方法中

这个方法有点复杂，逻辑量有点大

Step4:接着来看看scheduleBroadcastsLocked（）方法

Step5:履行消息BROADCAST_INTENT_MSG的地方：

以上方法履行processNextBroadcast(true);这个是最重要的调用广播发送的方法了。

Step6:processNextBroadcast（）方法的履行：

final void processNextBroadcast(boolean fromMsg) { synchronized(mService) { BroadcastRecord r; if (DEBUG_BROADCAST) Slog.v(TAG, "processNextBroadcast [" + mQueueName + "]: " + mParallelBroadcasts.size() + " broadcasts, " + mOrderedBroadcasts.size() + " ordered broadcasts"); mService.updateCpuStats(); if (fromMsg) { //这个表示前面的Scheduled还没有履行，handleMessage中会接着处理 mBroadcastsScheduled = false; } // First, deliver any non-serialized broadcasts right away. //mParallelBroadcasts这个就是1个无序的广播调度队列 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, "Processing parallel broadcast [" + mQueueName + "] " + r); for (int i=0; i<N; i++) { Object target = r.receivers.get(i); if (DEBUG_BROADCAST) Slog.v(TAG, "Delivering non-ordered on [" + mQueueName + "] to registered " + target + ": " + r); //调用无序广播 deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false); } addBroadcastToHistoryLocked(r); if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG, "Done with parallel broadcast [" + mQueueName + "] " + r); } // Now take care of the next serialized one... // If we are waiting for a process to come up to handle the next // broadcast, then do nothing at this point. Just in case, we // check that the process we're waiting for still exists. //mPendingBroadcast 描写的广播的接收者有多是静态注册的。 if (mPendingBroadcast != null) { if (DEBUG_BROADCAST_LIGHT) { Slog.v(TAG, "processNextBroadcast [" + mQueueName + "]: waiting for " + mPendingBroadcast.curApp); } boolean isDead; synchronized (mService.mPidsSelfLocked) { ProcessRecord proc = mService.mPidsSelfLocked.get(mPendingBroadcast.curApp.pid); isDead = proc == null || proc.crashing; } //如果它运行中，保持等待 if (!isDead) { // It's still alive, so keep waiting return; } else { Slog.w(TAG, "pending app [" + mQueueName + "]" + mPendingBroadcast.curApp + " died before responding to broadcast"); mPendingBroadcast.state = BroadcastRecord.IDLE; //如果它没有运行，就准备给它发送1个广播mPendingBroadcastRecvIndex mPendingBroadcast.nextReceiver = mPendingBroadcastRecvIndex; mPendingBroadcast = null; } } boolean looped = false; //有序广播mOrderedBroadcasts的调度任务的处理 do { 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); boolean forceReceive = false; // Ensure that even if something goes awry with the timeout // detection, we catch "hung" broadcasts here, discard them, // and continue to make progress. // // This is only done if the system is ready so that PRE_BOOT_COMPLETED // receivers don't get executed with timeouts. They're intended for // one time heavy lifting after system upgrades and can take // significant amounts of time. int numReceivers = (r.receivers != null) ? r.receivers.size() : 0; if (mService.mProcessesReady && r.dispatchTime > 0) { long now = SystemClock.uptimeMillis(); //检查广播的的处理时间是不是在规定的时间完成 if ((numReceivers > 0) && (now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) { Slog.w(TAG, "Hung broadcast [" + mQueueName + "] discarded after timeout failure:"+ " now=" + now + " dispatchTime=" + r.dispatchTime + " startTime=" + r.receiverTime + " intent=" + r.intent + " numReceivers=" + numReceivers + " nextReceiver=" + r.nextReceiver + " state=" + r.state); //置为idle状态。 broadcastTimeoutLocked(false); // forcibly finish this broadcast forceReceive = true; r.state = BroadcastRecord.IDLE; } } if (r.state != BroadcastRecord.IDLE) { if (DEBUG_BROADCAST) Slog.d(TAG, "processNextBroadcast(" + mQueueName + ") called when not idle (state=" + r.state + ")"); return; } 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) { int seq = r.intent.getIntExtra("seq", -1); Slog.i(TAG, "Finishing broadcast [" + mQueueName + "] " + r.intent.getAction() + " seq=" + seq + " 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, "Cancelling BROADCAST_TIMEOUT_MSG"); //取消广播删除BROADCAST_TIMEOUT_MSG这个消息 cancelBroadcastTimeoutLocked(); if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG, "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... //获得下1个广播 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, "Processing ordered broadcast [" + mQueueName + <

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