【阅读笔记】Android广播的处理流程

关于Android的解析，有很多优质内容，看了后记录一下阅读笔记，也是一种有意义的事情，

今天就看看“那个写代码的”这位大佬关于广播的梳理，

https://blog.csdn.net/a572423926/category_11509429.html

https://blog.csdn.net/a572423926/article/details/121760258

广播的原理很清晰，类似一种观察者模式，控制中心把广播发送给注册者（观察者），但是android中的实现细节较多。

这里通过一个am命令发送受保护的广播，查看抛出的异常，看相关堆栈。

am broadcast -n com.example.test/.AppInstallReceiver -a android.intent.action.SCREEN_ON

am broadcast -n com.example.test/.AppInstallReceiver -a android.intent.action.SCREEN_ON
Broadcasting: Intent { act=android.intent.action.SCREEN_ON flg=0x400000 cmp=com.example.test/.AppInstallReceiver }

Exception occurred while executing 'broadcast':
java.lang.SecurityException: Permission Denial: not allowed to send broadcast android.intent.action.SCREEN_ON from pid=18179, uid=2000
        at com.android.server.am.ActivityManagerService.broadcastIntentLocked(ActivityManagerService.java:14369)
        at com.android.server.am.ActivityManagerService.broadcastIntentLocked(ActivityManagerService.java:14206)
        at com.android.server.am.ActivityManagerService.broadcastIntentWithFeature(ActivityManagerService.java:15092)
        at com.android.server.am.ActivityManagerShellCommand.runSendBroadcast(ActivityManagerShellCommand.java:806)
        at com.android.server.am.ActivityManagerShellCommand.onCommand(ActivityManagerShellCommand.java:221)
        at com.android.modules.utils.BasicShellCommandHandler.exec(BasicShellCommandHandler.java:97)
        at android.os.ShellCommand.exec(ShellCommand.java:38)
        at com.android.server.am.ActivityManagerService.onShellCommand(ActivityManagerService.java:9776)
        at android.os.Binder.shellCommand(Binder.java:1055)
        at android.os.Binder.onTransact(Binder.java:883)
        at android.app.IActivityManager$Stub.onTransact(IActivityManager.java:4845)
        at com.android.server.am.ActivityManagerService.onTransact(ActivityManagerService.java:2833)
        at android.os.Binder.execTransactInternal(Binder.java:1291)
        at android.os.Binder.execTransact(Binder.java:1250)

调用到ActivityManagerService.broadcastIntentLocked

app中发送广播后，会调用到ActivityManagerService.broadcastIntentLocked

在PMS中查询，有哪些接收者

这里可以把ResolveInfo打印出来进行查看接收者是否被筛选出来了，具体分析可查看原文。

然后，进行分发，

会调用到BroadcastQueue.java 的processNextBroadcast，有些广播接收不到，就是在这里面进行了屏蔽。

processNextBroadcast的代码设计不好，

对于并行广播，搞了个循环来一下子处理完成。

“processNextBroadcast 每次被调用，只能分发给 mOrderedBroadcasts 中一个广播的其中一个 Receiver，如果静态注册的应用未启动，还需要等待应用启动后再进行处理。”

/frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java

final void processNextBroadcast(boolean fromMsg) {
	synchronized(mService) {
		BroadcastRecord r;
		......
		
		// 这里的do-while只会从mOrderedBroadcasts中取出第一个BroadcastRecord进行后续的处理！
		do {
			......
			r = mOrderedBroadcasts.get(0);
			......
		} while (r == null);

		......
		
		final Object nextReceiver = r.receivers.get(recIdx); // 取出一个Receiver

		// 对动态注册receiver的处理，这里是分发有序广播
		if (nextReceiver instanceof BroadcastFilter) {
			......
			// 通过deliverToRegisteredReceiverLocked调用ActivityThread.scheduleRegisteredReceiver处理广播
			deliverToRegisteredReceiverLocked(r, filter, r.ordered, recIdx);
			......
		}

		// 开始对静态注册receiver的处理！！！
		ResolveInfo info = (ResolveInfo)nextReceiver;
		......

		// 如果应用已经启动，则直接分发广播给该应用，并返回
		if (app != null && app.thread != null && !app.killed) {
			try {
				app.addPackage(info.activityInfo.packageName,
						info.activityInfo.applicationInfo.versionCode, mService.mProcessStats);
				// 通过processCurBroadcastLocked -> ActivityThread.scheduleReceiver -> receiver.onReceive处理当前广播
				processCurBroadcastLocked(r, app);
				return;
			} catch (RemoteException e) {
				Slog.w(TAG, "Exception when sending broadcast to "
					  + r.curComponent, e);
			} catch (RuntimeException e) {
				Slog.wtf(TAG, "Failed sending broadcast to "
						+ r.curComponent + " with " + r.intent, e);
				......
				return;
			}
		}

		......

		// 如果应用未启动，则在这里启动应用进程，广播将在AMS启动完成后被调用处理
		if ((r.curApp=mService.startProcessLocked(targetProcess,
				info.activityInfo.applicationInfo, true,
				r.intent.getFlags() | Intent.FLAG_FROM_BACKGROUND,
				"broadcast", r.curComponent,
				(r.intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) != 0, false, false))
						== null) {
			Slog.w(TAG, "Unable to launch app "
                    + info.activityInfo.applicationInfo.packageName + "/"
                    + info.activityInfo.applicationInfo.uid + " for broadcast "
                    + r.intent + ": process is bad");
			......
			return;
		}

		// 将BroadcastRecord赋值为mPendingBroadcast，等待应用启动完成后处理
		mPendingBroadcast = r;
		mPendingBroadcastRecvIndex = recIdx;
	}
}

这里面

通过 deliverToRegisteredReceiverLocked 调用到 ActivityThread.scheduleRegisteredReceiver，处理动态注册的 receiver；通过 processCurBroadcastLocked，调用到 ActivityThread.scheduleReceiver，处理静态注册的 receiver

这样，就传送给app端了。

参考资料：https://blog.csdn.net/a572423926/article/details/121760258
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原文链接：https://blog.csdn.net/a572423926/article/details/121760258