Android Broadcast原理分析之sendBroadcast（二）

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目录

• 广播发送与派发整体流程简介
• sendBroadcast时序图
• 源码解析
• 总结

1. 广播发送与派发整体流程简介

从上一节广播的注册，可以知道广播机制是典型的观察者模式，那么通知所有receiver的时机具体是什么时候呢，答案就是在发送广播的时候，广播一发送，此时就应该通知所有已经注册的观察者，也就是已经注册的receiver。整个广播的派发的流程其实就是逐个通知观察者的过程。而这整体的流程主要都在BroadcastQueue中经过调度之后派发给各个注册的receiver，最终回调到APP进程中已注册的receiver的onReceive方法。

注：本文基于Android 8.1。

2. sendBroadcast时序图

1. 上面的流程中，主要涉及到的进程有发送APP的进程，systemserver进程，以及接收广播的进程
2. 图中11～18的过程是动态注册的广播的派发（包括有序和无序）
3. 图中19～24的过程是静态注册的派发，静态注册的广播默认都以有序广播形式派发
4. BroadcastHandler调度线程是用的ActivityManager线程

3. 源码解析

3.1 ContextImpl.sendBroadcast

客户端通过context发送广播，都会调用到ContextImpl.sendBroadcast去实现广播的发送，而且不管是发送有序广播还是无序广播，最终发起binder call的方法都是一致的。
sendBroadcast

    @Overridepublic void sendBroadcast(Intent intent, String receiverPermission, int appOp) {warnIfCallingFromSystemProcess();String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());String[] receiverPermissions = receiverPermission == null ? null: new String[] {receiverPermission};try {intent.prepareToLeaveProcess(this);ActivityManager.getService().broadcastIntent(mMainThread.getApplicationThread(), intent, resolvedType, null,Activity.RESULT_OK, null, null, receiverPermissions, appOp, null, false, false,getUserId());} catch (RemoteException e) {throw e.rethrowFromSystemServer();}}

sendOrderedBroadcast

    void sendOrderedBroadcast(Intent intent,String receiverPermission, int appOp, BroadcastReceiver resultReceiver,Handler scheduler, int initialCode, String initialData,Bundle initialExtras, Bundle options) {warnIfCallingFromSystemProcess();IIntentReceiver rd = null;// 相比于发送无序广播，有序广播最重要区别就在// 有序广播可以有一个resultRceiver，也就是可以指定这个广播的最后一个接收者// 有序广播是逐个派发的，因此通过最后一个接收者可以知道广播派发完毕了，做一些收尾工作if (resultReceiver != null) {if (mPackageInfo != null) {if (scheduler == null) {scheduler = mMainThread.getHandler();}rd = mPackageInfo.getReceiverDispatcher(resultReceiver, getOuterContext(), scheduler,mMainThread.getInstrumentation(), false);} else {if (scheduler == null) {scheduler = mMainThread.getHandler();}rd = new LoadedApk.ReceiverDispatcher(resultReceiver, getOuterContext(), scheduler, null, false).getIIntentReceiver();}}String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());String[] receiverPermissions = receiverPermission == null ? null: new String[] {receiverPermission};try {intent.prepareToLeaveProcess(this);ActivityManager.getService().broadcastIntent(mMainThread.getApplicationThread(), intent, resolvedType, rd,initialCode, initialData, initialExtras, receiverPermissions, appOp,options, true, false, getUserId());} catch (RemoteException e) {throw e.rethrowFromSystemServer();}}

上面resultReceiver跟receiver的注册有些类似，这也正是有序广播相对与无序广播多出来的部分，多了最后的InnerReceiver，保证本次发送的所有广播执行结束之后，调用这个广播。

3.2 ActivityManagerService.broadcastIntent

    public final int broadcastIntent(IApplicationThread caller,Intent intent, String resolvedType, IIntentReceiver resultTo,int resultCode, String resultData, Bundle resultExtras,String[] requiredPermissions, int appOp, Bundle bOptions,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, bOptions, serialized, sticky,callingPid, callingUid, userId);Binder.restoreCallingIdentity(origId);return res;}}

参数解析：
caller：发送方的applicationThread对象
intent：本次发送的广播所带的intent
resolvedType：根绝intent schema判断类型
resultTo：最终接受的receiver
resultCode：有序广播在一个receiver处理之后可以设置值，这样下一个receiver就可以拿到这个数据
resultData：作用同上面的code，是string类型的数据
resultExtras：作用同上面的code，是Bundle类型数据
requiredPermissions：接收这个广播需要的权限
appOp：接受这个广播需要的AppopsManager权限
bOptions：设置在这个广播发送的时候将某个package放入到deviceIdle白名单中，有时长限制
serialized：是否为有序广播
sticky：是否为sticky广播
userId：这个广播将要发送到的user

3.3 ActivityManagerService.broadcastIntentLocked

    final int broadcastIntentLocked(ProcessRecord callerApp,String callerPackage, Intent intent, String resolvedType,IIntentReceiver resultTo, int resultCode, String resultData,Bundle resultExtras, String[] requiredPermissions, int appOp, Bundle bOptions,boolean ordered, boolean sticky, int callingPid, int callingUid, int userId) {// Intent支持跨进程传输，保证互不干扰，此处创建新的Intent对象intent = new Intent(intent);final boolean callerInstantApp = isInstantApp(callerApp, callerPackage, callingUid);if (callerInstantApp) {// 如果caller是instant app，则不能使用FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS// 即instant app不能发送给instant app可见的广播intent.setFlags(intent.getFlags() & ~Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS);}// 默认情况下，广播不会发送给处于stop状态下的package// 应用在安装后从来没有启动过，或者已经被用户强制停止了，那么这个应用就处于停止状态intent.addFlags(Intent.FLAG_EXCLUDE_STOPPED_PACKAGES);// 如果开机还没有完成，且没有带升级状态可接受的flag，那么添加FLAG_RECEIVER_REGISTERED_ONLYif (!mProcessesReady && (intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) == 0) {intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);}...// user校验// 参数中的bOptions会改变deviceidle的临时白名单// 因此需要查看caller是否有改变deviceidle名单的权限BroadcastOptions brOptions = null;if (bOptions != null) {brOptions = new BroadcastOptions(bOptions);if (brOptions.getTemporaryAppWhitelistDuration() > 0) {if (checkComponentPermission(android.Manifest.permission.CHANGE_DEVICE_IDLE_TEMP_WHITELIST,Binder.getCallingPid(), Binder.getCallingUid(), -1, true)!= PackageManager.PERMISSION_GRANTED) {String msg = "Permission Denial: " + intent.getAction()+ " broadcast from " + callerPackage + " (pid=" + callingPid+ ", uid=" + callingUid + ")"+ " requires "+ android.Manifest.permission.CHANGE_DEVICE_IDLE_TEMP_WHITELIST;Slog.w(TAG, msg);throw new SecurityException(msg);}}}// 确保protectBroadcast广播只能由某些特定的发送者发送// 主要是root/system/phone/bluetooth/nfc这些uid// 以及persist应用可以发送final String action = intent.getAction();final boolean isProtectedBroadcast;try {isProtectedBroadcast = AppGlobals.getPackageManager().isProtectedBroadcast(action);} catch (RemoteException e) {return ActivityManager.BROADCAST_SUCCESS;}final boolean isCallerSystem;switch (UserHandle.getAppId(callingUid)) {case ROOT_UID:case SYSTEM_UID:case PHONE_UID:case BLUETOOTH_UID:case NFC_UID:isCallerSystem = true;break;default:isCallerSystem = (callerApp != null) && callerApp.persistent;break;}if (!isCallerSystem) {// protectBroadcast只能由系统发送if (isProtectedBroadcast) {String msg = "Permission Denial: not allowed to send broadcast "+ action + " from pid="+ callingPid + ", uid=" + callingUid;Slog.w(TAG, msg);throw new SecurityException(msg);} else if (AppWidgetManager.ACTION_APPWIDGET_CONFIGURE.equals(action)|| AppWidgetManager.ACTION_APPWIDGET_UPDATE.equals(action)) {// 对于这些比较特殊的广播，不允许caller为nullif (callerPackage == null) {String msg = "Permission Denial: not allowed to send broadcast "+ action + " from unknown caller.";Slog.w(TAG, msg);throw new SecurityException(msg);} else if (intent.getComponent() != null) {// 如果component不为空，则必须要求所设置的component的package和caller一致if (!intent.getComponent().getPackageName().equals(callerPackage)) {String msg = "Permission Denial: not allowed to send broadcast "+ action + " to "+ intent.getComponent().getPackageName() + " from "+ callerPackage;Slog.w(TAG, msg);throw new SecurityException(msg);}} else {// 如果component为空则只能发送给自己intent.setPackage(callerPackage);}}}if (action != null) {if (getBackgroundLaunchBroadcasts().contains(action)) {// 判断允许在后台应用可以接受的广播的action列表中有没有这个action/

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