发布时间 : 星期五 文章Android 7.0 ActivityManagerService(5) 广播(Broadcast)相关流程分析(1)更新完毕开始阅读
需要注意的是：
在onReceive函数中执行异步操作，主要目的是避免一些操作阻塞了主线程，
但整个操作仍然需要保证在10s内返回结果，尤其是处理有序广播和静态广播时。 毕竟AMS必须要收到返回结果后，才能向下一个BroadcastReceiver发送广播。
2 AMS中的registerReceiver
AMS的registerReceiver函数被调用时，将会保存BroadcastReceiver对应的Binder通信端，我们一起来看看这部分的代码：
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId) { ...............
//保存系统内已有的sticky广播
ArrayList
synchronized(this) { if (caller != null) {
//根据IApplicationThread得到对应的进程信息 callerApp = getRecordForAppLocked(caller);
if (callerApp == null) {
//抛出异常，即不允许未登记的进程注册BroadcastReceiver ............... }
if (callerApp.info.uid != Process.SYSTEM_UID &&
!callerApp.pkgList.containsKey(callerPackage) && !\
//抛出异常，即注册进程必须携带Package名称 .................. } } else {
............. }
......................
//为了得到IntentFilter中定义的Action信息，先取出其Iterator Iterator
ArrayList
actions = noAction.iterator(); }
// Collect stickies of users
int[] userIds = { UserHandle.USER_ALL, UserHandle.getUserId(callingUid) }; while (actions.hasNext()) {
//依次比较BroadcastReceiver关注的Action与Stick广播是否一致 String action = actions.next(); for (int id : userIds) {
ArrayMap
//Sticky广播中，有BroadcastReceiver关注的
//可能有多个Intent，对应的Action相似，在此先做一个初步筛选 ArrayList
if (stickyIntents == null) {
stickyIntents = new ArrayList
//将这些广播保存到stickyIntents中 stickyIntents.addAll(intents); } } } } }
ArrayList
//stickyIntents中保存的是action匹配的 if (stickyIntents != null) { //用于解析intent的type
final ContentResolver resolver = mContext.getContentResolver();
// Look for any matching sticky broadcasts...
for (int i = 0, N = stickyIntents.size(); i < N; i++) { Intent intent = stickyIntents.get(i);
//此时进一步判断Intent与BroadcastReceiver的IntentFilter是否匹配 if (filter.match(resowww.sm136.comlver, intent, true, TAG) >= 0) { if (allSticky == null) {
allSticky = new ArrayList
allSticky.add(intent); } } }
// The first sticky in the list is returned directly back to the client. Intent sticky = allSticky != null ? allSticky.get(0) : null; ................
synchronized (this) { ..............
//一个Receiver可能监听多个广播，多个广播对应的BroadcastFilter组成ReceiverList ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder()); if (rl == null) {
//首次注册，rl为null，进入此分支
//新建BroadcastReceiver对应的ReceiverList
rl = new ReceiverList(this, callerApp, callingPid, callingUid, userId, receiver); if (rl.app != null) {
rl.app.receivers.add(rl); } else { try {
//rl监听receiver所在进程的死亡消息 receiver.asBinder().linkToDeath(rl, 0); } catch (RemoteException e) { return sticky; }
rl.linkedToDeath = true; }
//保存到AMS上
mRegisteredReceivers.put(receiver.asBinder(), rl); } .......... ............
//创建当前IntentFilter对应的BroadcastFilter
//AMS收到广播后，将根据BroadcastFilter决定是否将广播递交给对应的BroadcastReceiver
//一个BroadcastReceiver可以对应多个IntentFilter
//这些IntentFilter对应的BroadcastFilter共用一个ReceiverList BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage, permission, callingUid, userId); rl.add(bf); ................
mReceiverResolver.addFilter(bf);
// Enqueue broadcasts for all existing stickies that match // this filter.
//allSticky不为空，说明有粘性广播需要发送给刚注册的BroadcastReceiver if (allSticky != null) {
ArrayList receivers = new ArrayList(); //receivers记录bf receivers.add(bf);
final int stickyCount = allSticky.size(); for (int i = 0; i < stickyCount; i++) { Intent intent = allSticky.get(i);
//根据intent的flag （FLAG_RECEIVER_FOREGROUND）决定是使用gBroadcastQueue还是BgBroadcastQueue
BroadcastQueue queue = broadcastQueueForIntent(intent);
//创建广播对应的BroadcastRecord
//BroadcastRecord中包含了Intent，即知道要发送什么广播；
//同时其中含有receivers，内部包含bf，即知道需要将广播发送给哪个BroadcastReceiver
BroadcastRecord r = new BroadcastRecord(queue, intent, null,
null, -1, -1, null, null, AppOpsManager.OP_NONE, null, receivers, null, 0, null, null, false, true, true, -1);
//加入到BroadcastQueue中，存入的是并发广播对应的队列 queue.enqueueParallelBroadcastLocked(r);
//将发送BROADCAST_INTENT_MSG，触发AMS发送广播 queue.scheduleBroadcastsLocked(); } } } }
至此，AMS中registerReceiver的流程结束。
这个函数看起来很长，但主要工作还是比较清晰的，一共可以分为两个部分：
1、将BroadcastReceiver对应的信息保存到AMS中，同时为当前使用的IntentFilter生成对应的BroadcastFilter。 当AMS发送广播时，将根据广播和BroadcastFilter的匹配情况，决定是否为BroadcastReceiver发送消息。
2、单独对粘性广播进行处理。
由于粘性广播有立即发送的特点，因此当有新的BroadcastReceiver注册到AMS后， AMS需要判断系统中保存的粘性广播中，是否有与该BroadcastReceiver匹配的。
若有与新注册BroadcastReceiver匹配的粘性广播，那么AMS为这些广播构造BroadcastRecord，
并将其加入到发送队列中，同时发送消息触发AMS的广播发送流程。
上述代码的整个过程，还是比较好理解的，唯一麻烦一点的就是涉及到了一些数据结构，需