4 廣播的處理
廣播的處理都會調用BroadcastQueue下的scheduleBroadcastsLocked（），接下我們來看看這個函數
4.1 scheduleBroadcastsLocked
文件：BroadcastQueue.java
public void scheduleBroadcastsLocked() {
if (mBroadcastsScheduled) {
return;
}
// 見4.1.1
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
mBroadcastsScheduled = true;
}mBroadcastsScheduled這個boolean的意思是如果當前真好有一個BROADCAST_INTENT_MSG在執行，那麼mBroadcastsScheduled爲true，否則爲false
4.1.1 BroadcastHandler
文件：BroadcastQueue.java
private final class BroadcastHandler extends Handler {
......
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case BROADCAST_INTENT_MSG: {
// 見4.2
processNextBroadcast(true);
} break;
......
}
}
}最重要的就是processNextBroadcast，廣播處理會多次調用它
4.2 processNextBroadcast
文件：BroadcastQueue.java
這個函數有500多行，我們分開來講
4.2.1 非串行廣播的處理
// 如果是從BroadcastHandler中調用來的，則fromMsg爲true，mBroadcastsScheduled爲false
if (fromMsg) {
mBroadcastsScheduled = false;
}
// 首先，立即發送所有的非串行廣播
while (mParallelBroadcasts.size() > 0) {
r = mParallelBroadcasts.remove(0); // 每次都從一個開始
r.dispatchTime = SystemClock.uptimeMillis(); // 分發時間
r.dispatchClockTime = System.currentTimeMillis(); // 分發時間
final int N = r.receivers.size();
for (int i=0; i<N; i++) {
Object target = r.receivers.get(i);
// 將廣播發給BroadcastRecord所有的Receiver，見4.3
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);
}
addBroadcastToHistoryLocked(r); //將廣播添加歷史統計
}這部分主要是對非串行廣播進行發送，通過兩層循環來發送所有的Receiver，接下來看看串行發送的廣播
4.2.2 串行廣播的處理
if (mPendingBroadcast != null) {
boolean isDead;
synchronized (mService.mPidsSelfLocked) {
// 拿到正在處理廣播的進程，並判斷它是否死亡
ProcessRecord proc = mService.mPidsSelfLocked.get(mPendingBroadcast.curApp.pid);
isDead = proc == null || proc.crashing;
}
if (!isDead) {
// 如果處理廣播的進程保持活躍狀態，則繼續等待
return;
} else {
mPendingBroadcast.state = BroadcastRecord.IDLE;
mPendingBroadcast.nextReceiver = mPendingBroadcastRecvIndex;
mPendingBroadcast = null;
}
}
判斷處理廣播的進程是否保持活躍狀態，如果是，則繼續等待其完成
boolean looped = false;
do {
if (mOrderedBroadcasts.size() == 0) {
// 所有串行廣播執行完畢，則執行GC操作
mService.scheduleAppGcsLocked();
if (looped) {
mService.updateOomAdjLocked();
}
return;
}
// 拿串行廣播中的第一個
r = mOrderedBroadcasts.get(0);
boolean forceReceive = false;
// 該ReceiverList中所有接收者的數量
int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
// AMS已經註冊啓動完成，並且不是該r第一次進這個循環了
if (mService.mProcessesReady && r.dispatchTime > 0) {
long now = SystemClock.uptimeMillis()
// 出現超時
if ((numReceivers > 0) &&
(now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {
broadcastTimeoutLocked(false); // 強制結束這個廣播
forceReceive = true;
r.state = BroadcastRecord.IDLE;
}
}
if (r.state != BroadcastRecord.IDLE) {
return;
}
每次都會取mOrderedBroadcasts中的第一個元素，然後判斷是否超時，如果超時，則強制結束這個廣播，並且這個BroadcastRecord剩下的廣播接收器也將收不到廣播。超時的依據是：2*mTimeoutPeriod*numReceivers，其中mTimeoutPeriod爲（前臺廣播爲10s，後臺廣播爲60s），numReceivers爲接收器的數量；接着如果BroadcastRecord的state不等於BroadcastRecord.IDLE，就返回
// 要麼是廣播已經向所有的receiver發送完畢，要麼是被強制停止
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {
if (r.resultTo != null) {
try {
// 處理廣播消息，調用onReceive()，見4.3.1
performReceiveLocked(r.callerApp, r.resultTo,
new Intent(r.intent), r.resultCode,
r.resultData, r.resultExtras, false, false, r.userId);
r.resultTo = null;
} catch (RemoteException e) {
r.resultTo = null;
}
}
// 取消BROADCAST_TIMEOUT_MSG消息，見4.2.3
cancelBroadcastTimeoutLocked();
addBroadcastToHistoryLocked(r);
if (r.intent.getComponent() == null && r.intent.getPackage() == null
&& (r.intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
mService.addBroadcastStatLocked(r.intent.getAction(), r.callerPackage,
r.manifestCount, r.manifestSkipCount, r.finishTime-r.dispatchTime);
}
mOrderedBroadcasts.remove(0);
r = null;
looped = true;
continue;
}
} while (r == null);當Broadcasts中所有的receiver都收到了廣播或者被強制結束了廣播，都會調用performReceiveLocked；另外如果是取到BroadcastRecord第一次進來這個循環，將之前出來，因爲不滿足while (r == null)
// 獲取下一個需要處理的Receiver的序號
int recIdx = r.nextReceiver++;
// 這個BroadcastRecord開始處理這個Receiver的時間
r.receiverTime = SystemClock.uptimeMillis();
// 如果是BroadcastRecord中第一個Receiver
if (recIdx == 0) {
r.dispatchTime = r.receiverTime;
r.dispatchClockTime = System.currentTimeMillis();
}
if (! mPendingBroadcastTimeoutMessage) {
long timeoutTime = r.receiverTime + mTimeoutPeriod;
// 見4.2.4
setBroadcastTimeoutLocked(timeoutTime);
}獲取下一個要處理的Receiver
獲取當前處理這個Receiver的時間，用於處理ANR問題，如果是當前處理的是第一個Receiver，你們dispatchTime時間和receiverTime相等，用於處理整個BroadcastRecord的超時問題
mPendingBroadcastTimeoutMessage的初始值是false，然後設置針對該Receiver的超時處理，超時就會造成ANR；超時的時間爲10s（前臺廣播）或者60s（後臺廣播）
final BroadcastOptions brOptions = r.options;
final Object nextReceiver = r.receivers.get(recIdx);
// 如果是動態註冊的有序廣播
if (nextReceiver instanceof BroadcastFilter) {
BroadcastFilter filter = (BroadcastFilter)nextReceiver;
// 發送該動態註冊的有序廣播，見4.3
deliverToRegisteredReceiverLocked(r, filter, r.ordered, recIdx);
if (r.receiver == null || !r.ordered) {
r.state = BroadcastRecord.IDLE;
scheduleBroadcastsLocked();
} else {
if (brOptions != null && brOptions.getTemporaryAppWhitelistDuration() > 0) {
scheduleTempWhitelistLocked(filter.owningUid,
brOptions.getTemporaryAppWhitelistDuration(), r);
}
}
return;
}判斷當前這個接收器是不是動態註冊的，如果是動態註冊的，就用deliverToRegisteredReceiverLocked發送，最後return，結束processNextBroadcast這個函數
ResolveInfo info =
(ResolveInfo)nextReceiver;
ComponentName component = new ComponentName(
info.activityInfo.applicationInfo.packageName,
info.activityInfo.name);
......// 主要進行一些權限檢查，如果不滿足條件skip置爲true，跳過這個receiver
if (skip) {
r.delivery[recIdx] = BroadcastRecord.DELIVERY_SKIPPED;
r.receiver = null;
r.curFilter = null;
r.state = BroadcastRecord.IDLE;
scheduleBroadcastsLocked();
return;
}
r.delivery[recIdx] = BroadcastRecord.DELIVERY_DELIVERED;
r.state = BroadcastRecord.APP_RECEIVE;
r.curComponent = component;
r.curReceiver = info.activityInfo;
if (brOptions != null && brOptions.getTemporaryAppWhitelistDuration() > 0) {
scheduleTempWhitelistLocked(receiverUid,
brOptions.getTemporaryAppWhitelistDuration(), r);
}
// 廣播已經開始執行了，這個包不能被停止
try {
AppGlobals.getPackageManager().setPackageStoppedState(
r.curComponent.getPackageName(), false, UserHandle.getUserId(r.callingUid));
} catch (RemoteException e) {
} catch (IllegalArgumentException e) {
Slog.w(TAG, "Failed trying to unstop package "
+ r.curComponent.getPackageName() + ": " + e);
}
// 檢查目標進程是否已經運行
if (app != null && app.thread != null) {
try {
app.addPackage(info.activityInfo.packageName,
info.activityInfo.applicationInfo.versionCode, mService.mProcessStats);
//將廣播發送給目標進程，見4.2.5
processCurBroadcastLocked(r, app);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when sending broadcast to "
+ r.curComponent, e);
} catch (RuntimeException e) {
logBroadcastReceiverDiscardLocked(r);
finishReceiverLocked(r, r.resultCode, r.resultData,
r.resultExtras, r.resultAbort, false);
scheduleBroadcastsLocked();
// 如果啓動receiver失敗，需要重置state
r.state = BroadcastRecord.IDLE;
return;
}
}
// 如果目標進程沒有啓動，則需要將他啓動，見4.2.6
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) {
// 這個接收器不能使用
logBroadcastReceiverDiscardLocked(r);
finishReceiverLocked(r, r.resultCode, r.resultData,
r.resultExtras, r.resultAbort, false);
scheduleBroadcastsLocked();
r.state = BroadcastRecord.IDLE;
return;
}
mPendingBroadcast = r;
mPendingBroadcastRecvIndex = recIdx;處理靜態註冊下廣播的發送，如果進程已經啓動，則用processCurBroadcastLocked發送，然後返回，AMS等待廣播接收的結果，以便進行下一個receiver發送廣播，如果超時，就會觸發ANR；
如果沒有啓動，則AMS調用startProcessLocked來啓動接收者進程，啓動的時候，將當前這個BroadcastRecord放到mPendingBroadcast中保存，把receiver的序號放到mPendingBroadcastRecvIndex中保存，應用啓動完畢後會通知AMS，然後在進行廣播發送
4.2.3 cancelBroadcastTimeoutLocked 取消超時
文件：BroadcastQueue.java
final void cancelBroadcastTimeoutLocked() {
if (mPendingBroadcastTimeoutMessage) {
mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);
mPendingBroadcastTimeoutMessage = false;
}
}意思就是移除BROADCAST_TIMEOUT_MSG這個消息，不進行超時的處理了
4.2.4 setBroadcastTimeoutLocked 設置超時
final void setBroadcastTimeoutLocked(long timeoutTime) {
if (! mPendingBroadcastTimeoutMessage) {
Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
mHandler.sendMessageAtTime(msg, timeoutTime);
mPendingBroadcastTimeoutMessage = true;
}
}由mHandler.sendMessageAtTime(msg, timeoutTime)可以看出，如果超時了就會發送消息BROADCAST_TIMEOUT_MSG
4.2.5 processCurBroadcastLocked
文件：BroadcastQueue.java
private final void processCurBroadcastLocked(BroadcastRecord r,
ProcessRecord app) throws RemoteException {
if (app.thread == null) {
throw new RemoteException();
}
if (app.inFullBackup) {
skipReceiverLocked(r);
return;
}
r.receiver = app.thread.asBinder();
r.curApp = app;
app.curReceiver = r;
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_RECEIVER);
mService.updateLruProcessLocked(app, false, null);
mService.updateOomAdjLocked();
// 告訴應用啓動receiver.
r.intent.setComponent(r.curComponent);
boolean started = false;
try {
mService.notifyPackageUse(r.intent.getComponent().getPackageName(),
PackageManager.NOTIFY_PACKAGE_USE_BROADCAST_RECEIVER);
// 見4.4處理靜態廣播
app.thread.scheduleReceiver(new Intent(r.intent), r.curReceiver,
mService.compatibilityInfoForPackageLocked(r.curReceiver.applicationInfo),
r.resultCode, r.resultData, r.resultExtras, r.ordered, r.userId,
app.repProcState);
started = true;
} finally {
if (!started) {
r.receiver = null;
r.curApp = null;
app.curReceiver = null;
}
}
}這裏最重要的是scheduleReceiver
4.2.6 啓動進程後通知AMS
流程如下：
ActivityThread.Main
ActivityThread.attach
AMS. attachApplication
AMS. attachApplicationLocked
到了attachApplicationLocked之後裏面一行這樣的代碼：
didSomething |= sendPendingBroadcastsLocked(app);我們繼續看看sendPendingBroadcastsLocked
boolean sendPendingBroadcastsLocked(ProcessRecord app) {
boolean didSomething = false;
for (BroadcastQueue queue : mBroadcastQueues) {
didSomething |= queue.sendPendingBroadcastsLocked(app);
}
return didSomething;
}主要是這行didSomething |= queue.sendPendingBroadcastsLocked(app)，我們繼續追
public boolean sendPendingBroadcastsLocked(ProcessRecord app) {
boolean didSomething = false;
final BroadcastRecord br = mPendingBroadcast;
if (br != null && br.curApp.pid == app.pid) {
if (br.curApp != app) {
return false;
}
try {
mPendingBroadcast = null;
// 發送廣播，見4.2.5
processCurBroadcastLocked(br, app);
didSomething = true;
} catch (Exception e) {
logBroadcastReceiverDiscardLocked(br);
finishReceiverLocked(br, br.resultCode, br.resultData,
br.resultExtras, br.resultAbort, false);
scheduleBroadcastsLocked();
// We need to reset the state if we failed to start the receiver.
br.state = BroadcastRecord.IDLE;
throw new RuntimeException(e.getMessage());
}
}
return didSomething;
}從mPendingBroadcast取出正在等待的BroadcastRecord，然後將mPendingBroadcast置爲null，接着用processCurBroadcastLocked發送廣播
4.3 deliverToRegisteredReceiverLocked 用來發送所有動態註冊的廣播
文件：BroadcastQueue.java
private void deliverToRegisteredReceiverLocked(BroadcastRecord r,
BroadcastFilter filter, boolean ordered, int index) {
boolean skip = false;
if (filter.requiredPermission != null) {
int perm = mService.checkComponentPermission(filter.requiredPermission,
r.callingPid, r.callingUid, -1, true);
// 如果接收者沒有權限，skip爲true
if (perm != PackageManager.PERMISSION_GRANTED) {
skip = true;
}
......
}
...... //中間這很長一大串代碼都是用來檢查權限，如果不符合要求skip會置爲true
if (skip) {
// 將狀態改爲DELIVERY_SKIPPED
r.delivery[index] = BroadcastRecord.DELIVERY_SKIPPED;
return;
}
// 複查一下權限
if (Build.PERMISSIONS_REVIEW_REQUIRED) {
if (!requestStartTargetPermissionsReviewIfNeededLocked(r, filter.packageName,
filter.owningUserId)) {
r.delivery[index] = BroadcastRecord.DELIVERY_SKIPPED;
return;
}
}
r.delivery[index] = BroadcastRecord.DELIVERY_DELIVERED;
// 如果是有序的動態廣播
if (ordered) {
r.receiver = filter.receiverList.receiver.asBinder();
r.curFilter = filter;
filter.receiverList.curBroadcast = r;
r.state = BroadcastRecord.CALL_IN_RECEIVE;
if (filter.receiverList.app != null) {
r.curApp = filter.receiverList.app;
filter.receiverList.app.curReceiver = r;
mService.updateOomAdjLocked(r.curApp);
}
}
try {
if (filter.receiverList.app != null && filter.receiverList.app.inFullBackup) {
if (ordered) {
skipReceiverLocked(r);
}
} else {
// 發送動態註冊的廣播，見4.3.1
performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,
new Intent(r.intent), r.resultCode, r.resultData,
r.resultExtras, r.ordered, r.initialSticky, r.userId);
}
if (ordered) {
r.state = BroadcastRecord.CALL_DONE_RECEIVE;
}
}
......
}進來時首先檢查權限，不滿足的將skip設置爲true，並將對應的receiver的狀態設置爲DELIVERY_DELIVERED
如果是有序的動態廣播，以一種同步的方式發送廣播，並且在BroadcastRecord中保存receiver，curFilter和state，其中state爲CALL_IN_RECEIVE
通過performReceiveLocked發送動態註冊的廣播
如果有序的動態廣播，state改爲CALL_DONE_RECEIVE
4.3.1 performReceiveLocked
文件：BroadcastQueue.java
void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
Intent intent, int resultCode, String data, Bundle extras,
boolean ordered, boolean sticky, int sendingUser) throws RemoteException {
// 進程已經啓動的情況，用binder異步機制向receiver發送數據
if (app != null) {
if (app.thread != null) {
try {
// 見4.3.2
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
data, extras, ordered, sticky, sendingUser, app.repProcState);
} catch (RemoteException ex) {
synchronized (mService) {
app.scheduleCrash("can't deliver broadcast");
}
throw ex;
}
} else {
// 應用已經死亡，Receiver不存在
throw new RemoteException("app.thread must not be null");
}
} else {
// 調用進程爲null時，則走這個分支
receiver.performReceive(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
}
}這裏分爲兩種情況：
調用進程和app.thread都不爲null，這時通過binder方式向註冊進程發起調用，其中Binder調用裏會加上IBinder.FLAG_ONEWAY標記
調用流程爲：調用進程爲null，這時執行receiver.performReceive(intent, resultCode, data, extras, ordered,sticky, sendingUser);
其中app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,data, extras, ordered, sticky, sendingUser, app.repProcState)的調用流程爲：
ApplicationThreadNative.ApplicationThreadProxy. scheduleRegisteredReceiver(system_server進程)
Binder驅動（Binder驅動進程，ONEWAY）
ApplicationThreadNative. scheduleRegisteredReceiver(應用進程，Binder線程向主線程發送消息)
Binder驅動返回 (Binder驅動進程)
ActivityThread. scheduleRegisteredReceiver(應用進程，處理消息)
4.3.2 scheduleRegisteredReceiver
public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
int resultCode, String dataStr, Bundle extras, boolean ordered,
boolean sticky, int sendingUser, int processState) throws RemoteException {
updateProcessState(processState, false);
// 見4.3.3
receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
sticky, sendingUser);
}4.3.3 performReceive
這是LoadedApk.ReceiverDispatcher.InnerReceiver.performReceive
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
final LoadedApk.ReceiverDispatcher rd;
......
if (rd != null) {
// 見4.3.4
rd.performReceive(intent, resultCode, data, extras,
ordered, sticky, sendingUser);
}
......
}4.3.4 ReceiverDispatcher.performReceive
文件：LoadedApk.java
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
// 見4.3.5
final Args args = new Args(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
if (intent == null) {
Log.wtf(TAG, "Null intent received");
} else {
if (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction()
+ " seq=" + seq + " to " + mReceiver);
}
}
// 將廣播信息放到args中，post到主線程中執行，見4.3.5
if (intent == null || !mActivityThread.post(args)) {
if (mRegistered && ordered) {
IActivityManager mgr = ActivityManagerNative.getDefault();
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing sync broadcast to " + mReceiver);
// 告訴AMS，廣播處理完畢，動態的有序廣播會走這裏見4.3.6
args.sendFinished(mgr);
}
}
}4.3.5 Args
final class Args extends BroadcastReceiver.PendingResult implements Runnable {
private Intent mCurIntent;
private final boolean mOrdered;
private boolean mDispatched;
public Args(Intent intent, int resultCode, String resultData, Bundle resultExtras,
boolean ordered, boolean sticky, int sendingUser) {
super(resultCode, resultData, resultExtras,
mRegistered ? TYPE_REGISTERED : TYPE_UNREGISTERED, ordered,
sticky, mIIntentReceiver.asBinder(), sendingUser, intent.getFlags());
mCurIntent = intent;
mOrdered = ordered;
}
public void run() {
final BroadcastReceiver receiver = mReceiver;
final boolean ordered = mOrdered;
final IActivityManager mgr = ActivityManagerNative.getDefault();
final Intent intent = mCurIntent;
if (intent == null) {
Log.wtf(TAG, "Null intent being dispatched, mDispatched=" + mDispatched);
}
mCurIntent = null;
mDispatched = true;
if (receiver == null || intent == null || mForgotten) {
if (mRegistered && ordered) {
sendFinished(mgr);
}
return;
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveReg");
try {
ClassLoader cl = mReceiver.getClass().getClassLoader();
intent.setExtrasClassLoader(cl);
intent.prepareToEnterProcess();
setExtrasClassLoader(cl);
receiver.setPendingResult(this);
// 調用接收者BroadcastReceiver.onReceive()
receiver.onReceive(mContext, intent);
} catch (Exception e) {
if (mRegistered && ordered) {
sendFinished(mgr);
}
if (mInstrumentation == null ||
!mInstrumentation.onException(mReceiver, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw new RuntimeException(
"Error receiving broadcast " + intent
+ " in " + mReceiver, e);
}
}
if (receiver.getPendingResult() != null) {
// 見4.3.6
finish();
}
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}這裏主要調用的是receiver.onReceive(mContext, intent)，至此非串行的動態註冊的廣播已經接收完畢，值得一提的是下面那個finish()函數，作用是結束這個廣播，並將結果發送給下一個廣播
4.3.6 sendFinished
文件：BroadcastReceiver.java
public void sendFinished(IActivityManager am) {
synchronized (this) {
if (mFinished) {
throw new IllegalStateException("Broadcast already finished");
}
mFinished = true;
try {
if (mResultExtras != null) {
mResultExtras.setAllowFds(false);
}
// 是否是有序的
if (mOrderedHint) {
// 見4.3.7
am.finishReceiver(mToken, mResultCode, mResultData, mResultExtras,
mAbortBroadcast, mFlags);
} else {
// 什麼都不幹，目的是告訴ActivityManager，這個廣播我處理我完了
am.finishReceiver(mToken, 0, null, null, false, mFlags);
}
} catch (RemoteException ex) {
}
}
}通過前面的分析，我們知道，動態廣播如果是無序，在執行finish的時候，因爲mType等於TYPE_REGISTERED，ordered爲false，所以什麼都不執行；只有有序的動態廣播最終調用sendFinished，走mOrderedHint爲true的那條線路，這裏面mAbortBroadcast值得注意，如果爲true，級別高的接收器收到廣播後，級別低的就收不到廣播了，好了，我們來看看finishReceiver，看這裏函數你能知道動態的廣播爲什麼可以循環起來
4.3.7 finishReceiver
文件：ActivityManagerService.java
public void finishReceiver(IBinder who, int resultCode, String resultData,
Bundle resultExtras, boolean resultAbort, int flags) {
// Refuse possible leaked file descriptors
if (resultExtras != null && resultExtras.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Bundle");
}
final long origId = Binder.clearCallingIdentity();
try {
boolean doNext = false;
BroadcastRecord r;
synchronized(this) {
BroadcastQueue queue = (flags & Intent.FLAG_RECEIVER_FOREGROUND) != 0
? mFgBroadcastQueue : mBgBroadcastQueue;
r = queue.getMatchingOrderedReceiver(who);
if (r != null) {
doNext = r.queue.finishReceiverLocked(r, resultCode,
resultData, resultExtras, resultAbort, true);
}
}
if (doNext) {
// 處理下一條廣播
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}首先判斷是不是是前臺廣播還是後臺廣播，如果是後臺廣播則開始執行下一條廣播，值得一提的是resultAbort和mAbortBroadcast上面的一致，最終的影響是這行代碼：
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {4.4 scheduleReceiver處理靜態廣播
我們還是一步步來看，首先:
文件：ActivityThread.java
public final void scheduleReceiver(Intent intent, ActivityInfo info,
CompatibilityInfo compatInfo, int resultCode, String data, Bundle extras,
boolean sync, int sendingUser, int processState) {
updateProcessState(processState, false);
ReceiverData r = new ReceiverData(intent, resultCode, data, extras,
sync, false, mAppThread.asBinder(), sendingUser);
r.info = info;
r.compatInfo = compatInfo;
// 見4.4.1
sendMessage(H.RECEIVER, r);
}4.4.1 H
文件：ActivityThread.java
public void handleMessage(Message msg) {
switch (msg.what) {
......
case RECEIVER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp");
// 見4.4.2
handleReceiver((ReceiverData)msg.obj);
maybeSnapshot();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
......4.4.2 handleReceiver
文件：ActivityThread.java
private void handleReceiver(ReceiverData data) {
unscheduleGcIdler();
String component = data.intent.getComponent().getClassName();
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
IActivityManager mgr = ActivityManagerNative.getDefault();
BroadcastReceiver receiver;
try {
java.lang.ClassLoader cl = packageInfo.getClassLoader();
data.intent.setExtrasClassLoader(cl);
data.intent.prepareToEnterProcess();
data.setExtrasClassLoader(cl);
// 用反射的方式生成BroadcastReceiver
receiver = (BroadcastReceiver)cl.loadClass(component).newInstance();
} catch (Exception e) {
data.sendFinished(mgr);
throw new RuntimeException(
"Unable to instantiate receiver " + component
+ ": " + e.toString(), e);
}
try {
Application app = packageInfo.makeApplication(false, mInstrumentation);
ContextImpl context = (ContextImpl)app.getBaseContext();
sCurrentBroadcastIntent.set(data.intent);
receiver.setPendingResult(data);
// 調用目標Receiver的onReceive()
receiver.onReceive(context.getReceiverRestrictedContext(),
data.intent);
} catch (Exception e) {
data.sendFinished(mgr);
if (!mInstrumentation.onException(receiver, e)) {
throw new RuntimeException(
"Unable to start receiver " + component
+ ": " + e.toString(), e);
}
} finally {
sCurrentBroadcastIntent.set(null);
}
if (receiver.getPendingResult() != null) {
data.finish();
}
}用反射的方法獲得類，然後生成BroadcastReceiver，接着調用onReceive()方法
5 總結與建議
5.1 並行廣播和串行廣播的發送特點
這是發廣播給動態註冊接收器時的特點，採用異步的形式，廣播之間不會互相干擾
這是採用串行發送廣播的方式，採用的是同步的機制，根據優先級來發送，優先級高的receiver可以停止廣播想優先級低的發送；靜態註冊的Receiver和有序的動態註冊的Receiver均採用這個方式
5.2 廣播處理的流程圖
這張圖展示了有序和無序廣播的處理流程
5.3 廣播處理的時序圖
5.4 建議
判斷自己的所需要獲取的廣播是否能夠動態註冊獲取，因爲Google基於優化考慮，比如SCREEN_OFF或SCREEN_OFF已經不能通過靜態註冊來獲取了
不要在onReceiver中進行耗時的操作，如果必須要這樣做，可以發送Intent啓動一個service來做
如果需要一直對廣播保持監聽，建議使用靜態註冊，因爲靜態註冊就算是目標進程不在了也可以重啓，而動態註冊的Receiver的生命週期會受應用的影響，應用銷燬了，Receiver也就收不到廣播了
如果只在同一APP內部發送和接收廣播，將exported屬性設置成false，或者可以使用LocalBroadcastManager類（本地廣播）
廣播發送和接收建議帶上權限
如果在onReceive()中開了一個子線程來執行工作，會碰上onReceive()已經返回，而子線程還沒有做完工作的情況，這時候如果AMS結束了進程，這時子線程也會掛掉，但是工作卻沒有做完，可以利用要PendingResult來規避這個問題，一般finish()方法一般都是PendingResult不等於null的時候調用（參考4.3.6），使用方法如下：
public void onReceive(final Context context, final Intent intent) {
//得到PendingResult
final PendingResult result = goAsync();
//放到異步線程中執行
AsyncHandler.post(new Runnable() {
@Override
public void run() {
handleIntent(context, intent);//可進行一些耗時操作
result.finish();
}
});
}一旦調用goAsync()，那麼BroadcastReceiver中的PendingResult將爲null，這時finish方法得不到執行，AMS就收不到onReceive()執行完的消息，一直要到子線程調用result.finish()纔會知道，這個目的只是爲了不阻塞主線程，操作還是要在規定時間內完成