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一　概述

广播 (Broadcast) 机制用于进程/线程间通信，广播分为广播发送和广播接收两个过程，其中广播接收者 BroadcastReceiver 上篇文章已经介绍过了，本篇文章介绍广播的发送，从广播发送方式可分为三类：

普通广播：通过 Context.sendBroadcast() 发送，并行处理

广播在系统中以 BroadcastRecord 对象来记录, 该对象有几个时间相关的成员变量需要注意。

final class BroadcastRecord extends Binder {
       final ProcessRecord callerApp;//广播发送者所在进程    final String callerPackage;//广播发送者所在包名    final List receivers;//包括动态注册的BroadcastFilter和静态注册的ResolveInfo    final int callingPid;//广播发送者pid    final List receivers;//广播接收者    int nextReceiver;//下一个被执行的接收者    IBinder receiver;//当前正在处理的接收者    int anrCount;//广播ANR次数    long enqueueClockTime;//入队列时间，伴随着scheduleBroadcastsLocked    long dispatchTime;//分发时间    long dispatchClockTime;//分发时间，伴随着deliverToRegisteredReceiverLocked    long receiverTime;//接收时间(首次等于dispatchClockTime)    long finishTime;//广播完成时间，位于addBroadcastToHistoryLocked方法内}

我们这一节主要分析广播的注册流程，相关代码路径如下：

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.javaframeworks/base/services/core/java/com/android/server/pm/PackageManagerService.javaframeworks/base/services/core/java/com/android/server/pm/ComponentResolver.javaframeworks/base/services/core/java/com/android/server/am/BroadcastQueue.javaframeworks/base/services/core/java/com/android/server/am/BroadcastRecord.javaframeworks/base/core/java/android/app/ContextImpl.java

二　sendBroadcast流程

2.1 ContextImpl.sendBroadcast

frameworks/base/core/java/android/app/ContextImpl.java

@Overridepublic void sendBroadcast(Intent intent) {
       warnIfCallingFromSystemProcess();    String resolvedType =             intent.resolveTypeIfNeeded(getContentResolver());     intent.prepareToLeaveProcess(this);    ActivityManager.getService().broadcastIntent(            mMainThread.getApplicationThread(), intent, ......);}

2.2 ActivityManagerService.broadcastIntent

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

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();        try {
               return broadcastIntentLocked(callerApp,                 callerApp != null ? callerApp.info.packageName : null,                    ......);        } finally {
               Binder.restoreCallingIdentity(origId);        }    }}

2.3 ActivityManagerService.broadcastIntentLocked

final int broadcastIntentLocked(ProcessRecord callerApp,        String callerPackage, Intent intent, ......) {
       return broadcastIntentLocked(callerApp, callerPackage, ......);}

具体实现细节看下面代码：

final int broadcastIntentLocked(ProcessRecord callerApp,        String callerPackage, ......) {
       intent = new Intent(intent); //1.根据各种限制设置intent的flags: 比如Instant App不能使用//FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS, 广播不会发送到杀死的进程//系统还没启动不允许启动新进程//2.检查接收广播的userId是否正在运行//3.权限和限制检查: 如CHANGE_DEVICE_IDLE_TEMP_WHITELIST权限// START_ACTIVITIES_FROM_BACKGROUND权限, OP_RUN_ANY_IN_BACKGROUND操作权限//4.非系统用户不允许发送ProtectedBroadcast, 系统用户指//(ROOT_UID/SYSTEM_UID/PHONE_UID/BLUETOOTH_UID//NFC_UID/SE_UID/NETWORK_STACK_UID)    ......     userId = mUserController.handleIncomingUser(callingPid, ......);    boolean timeoutExempt = false;    final String action = intent.getAction();    if (action != null) {
           // 如果action所属Intent需要发送给未启动的或后台的进程        // 则Intent添加flags为FLAG_RECEIVER_INCLUDE_BACKGROUND        if (getBackgroundLaunchBroadcasts().contains(action)) {
               intent.addFlags(Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND);        }         //包管理器发出的和包移除相关的action的处理，如        //ACTION_UID_REMOVED/ACTION_PACKAGE_REMOVED        //ACTION_PACKAGE_CHANGED/...        ...    }    // sticky广播处理,常规的sendBroadcast发送的都是非sticky广播,走不到这里    if (sticky) {
           //权限和条件检查包括: Manifest.permission.BROADCAST_STICKY权限检查//requiredPermissions和Component为空检查, mStickyBroadcasts重复广播检查        ......         // 将发送的广播Intent替换或插入到mStickyBroadcasts队列中相应位置        ArrayMap
   
    > stickies =                mStickyBroadcasts.get(userId);        if (stickies == null) {
               stickies = new ArrayMap<>();            mStickyBroadcasts.put(userId, stickies);        }        ArrayList
    
      list = stickies.get(intent.getAction());        if (list == null) {
               list = new ArrayList<>();            stickies.put(intent.getAction(), list);        }        final int stickiesCount = list.size();        int i;        for (i = 0; i < stickiesCount; i++) {
               if (intent.filterEquals(list.get(i))) {
                   // This sticky already exists, replace it.                list.set(i, new Intent(intent));                break;            }        }        if (i >= stickiesCount) {
               list.add(new Intent(intent));        }    }     // 设置广播的目标用户数组users    int[] users;    if (userId == UserHandle.USER_ALL) {
           // 所有启动用户        users = mUserController.getStartedUserArray();    } else {
           // 特定用户        users = new int[] {
   userId};    }     // Figure out who all will receive this broadcast.     // 收集receivers列表组件信息.     List receivers = null;    if ((intent.getFlags() &            Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
           receivers =   collectReceiverComponents(intent, resolvedType, callingUid, users);    }     // 通过IntentResolver收集已注册的Receiver列表registeredReceivers    List
     
       registeredReceivers = null;    if (intent.getComponent() == null) {
           if (userId == UserHandle.USER_ALL && callingUid == SHELL_UID) {
               for (int i = 0; i < users.length; i++) {
                   // 过滤Shell限制的用户                ......                 List
      
        registeredReceiversForUser =                        mReceiverResolver.queryIntent(intent, ......);                if (registeredReceivers == null) {
                       registeredReceivers = registeredReceiversForUser;                } else if (registeredReceiversForUser != null) {
                 registeredReceivers.addAll(registeredReceiversForUser);                }            }        } else {
               registeredReceivers =            mReceiverResolver.queryIntent(intent, ......);        }    }     final boolean replacePending = (intent.getFlags()&            Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;     // 整体逻辑: 将新发送的无序广播入队列    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.        if (isCallerSystem) {
               checkBroadcastFromSystem(intent, callerApp, ......);        }        final BroadcastQueue queue = broadcastQueueForIntent(intent);        BroadcastRecord r =                 new BroadcastRecord(queue, intent, ......);        final boolean replaced = replacePending &&              (queue.replaceParallelBroadcastLocked(r) != null);        if (!replaced) {
               queue.enqueueParallelBroadcastLocked(r);            queue.scheduleBroadcastsLocked();        }        registeredReceivers = null;        NR = 0;    }     // Merge into one list receivers.    // 1.receivers中移除如下action对应的广播: ACTION_PACKAGE_ADDED    //ACTION_PACKAGE_RESTARTED/ACTION_PACKAGE_DATA_CLEARED    //ACTION_EXTERNAL_APPLICATIONS_AVAILABLE    // 2.将registeredReceivers列表合并到receivers列表    ...    if (isCallerSystem) {
           checkBroadcastFromSystem(intent, callerApp, ......);    }     // 将新发送的有序广播入队列    if ((receivers != null && receivers.size() > 0) ||           resultTo != null) {
           BroadcastQueue queue = broadcastQueueForIntent(intent);        BroadcastRecord r = new BroadcastRecord(queue, intent, ......);         final BroadcastRecord oldRecord =         replacePending ? queue.replaceOrderedBroadcastLocked(r) : null;        if (oldRecord != null) {
               // Replaced, fire the result-to receiver.            if (oldRecord.resultTo != null) {
                   final BroadcastQueue oldQueue =                broadcastQueueForIntent(oldRecord.intent);                oldQueue.performReceiveLocked(oldRecord.callerApp, ......);            }        } else {
               queue.enqueueOrderedBroadcastLocked(r);            queue.scheduleBroadcastsLocked();        }    } else {
           // 该广播没有广播接收器, 说明是隐式广播, 记录一下即可        if (intent.getComponent() == null                 && intent.getPackage() == null                && (intent.getFlags()                &Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
               addBroadcastStatLocked(intent.getAction(), ......);        }    }     return ActivityManager.BROADCAST_SUCCESS;}