ANR的原理是进行了超时告警，在执行一个需要被监控的任务时，注册一个超时提醒，如果很快执行好了，删除这个提醒，如果超时，这个提醒就被触发，这个超时处理是通过handler方式来调用的，这里我们来关注一个细节，任务在执行，超时处理显然应该是在另外一个线程里来进行监控的。这是显而易见的，这里我们就通过广播里的ANR处理来查看这个显而易见的线程问题，
在广播发送过程中，会调用到AMS中的
ActivityManagerService.java - Android社区 - https://www.androidos.net.cn/
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) {
r.queue.processNextBroadcastLocked(/*fromMsg=*/ false, /*skipOomAdj=*/ true);
}这是AMS中的一个线程，调用了BroadcastQueue中的processNextBroadcastLocked
final void processNextBroadcastLocked(boolean fromMsg, boolean skipOomAdj) {
BroadcastRecord r;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "processNextBroadcast ["
+ mQueueName + "]: "
+ mParallelBroadcasts.size() + " parallel broadcasts, "
+ mOrderedBroadcasts.size() + " ordered broadcasts");
mService.updateCpuStats();
if (fromMsg) {
mBroadcastsScheduled = false;
}
// First, deliver any non-serialized broadcasts right away.
while (mParallelBroadcasts.size() > 0) {
r = mParallelBroadcasts.remove(0);
r.dispatchTime = SystemClock.uptimeMillis();
r.dispatchClockTime = System.currentTimeMillis();
if (Trace.isTagEnabled(Trace.TRACE_TAG_ACTIVITY_MANAGER)) {
Trace.asyncTraceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER,
createBroadcastTraceTitle(r, BroadcastRecord.DELIVERY_PENDING),
System.identityHashCode(r));
Trace.asyncTraceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
createBroadcastTraceTitle(r, BroadcastRecord.DELIVERY_DELIVERED),
System.identityHashCode(r));
}
final int N = r.receivers.size();
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing parallel broadcast ["
+ mQueueName + "] " + r);
for (int i=0; i<N; i++) {
Object target = r.receivers.get(i);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Delivering non-ordered on [" + mQueueName + "] to registered "
+ target + ": " + r);
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);
}
addBroadcastToHistoryLocked(r);
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Done with parallel broadcast ["
+ mQueueName + "] " + r);
}
// Now take care of the next serialized one...
// If we are waiting for a process to come up to handle the next
// broadcast, then do nothing at this point. Just in case, we
// check that the process we're waiting for still exists.
if (mPendingBroadcast != null) {
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST,
"processNextBroadcast [" + mQueueName + "]: waiting for "
+ mPendingBroadcast.curApp);
boolean isDead;
if (mPendingBroadcast.curApp.pid > 0) {
synchronized (mService.mPidsSelfLocked) {
ProcessRecord proc = mService.mPidsSelfLocked.get(
mPendingBroadcast.curApp.pid);
isDead = proc == null || proc.crashing;
}
} else {
final ProcessRecord proc = mService.mProcessNames.get(
mPendingBroadcast.curApp.processName, mPendingBroadcast.curApp.uid);
isDead = proc == null || !proc.pendingStart;
}
if (!isDead) {
// It's still alive, so keep waiting
return;
} else {
Slog.w(TAG, "pending app ["
+ mQueueName + "]" + mPendingBroadcast.curApp
+ " died before responding to broadcast");
mPendingBroadcast.state = BroadcastRecord.IDLE;
mPendingBroadcast.nextReceiver = mPendingBroadcastRecvIndex;
mPendingBroadcast = null;
}
}
boolean looped = false;
do {
if (mOrderedBroadcasts.size() == 0) {
// No more broadcasts pending, so all done!
mService.scheduleAppGcsLocked();
if (looped) {
// If we had finished the last ordered broadcast, then
// make sure all processes have correct oom and sched
// adjustments.
mService.updateOomAdjLocked();
}
return;
}
r = mOrderedBroadcasts.get(0);
boolean forceReceive = false;
// Ensure that even if something goes awry with the timeout
// detection, we catch "hung" broadcasts here, discard them,
// and continue to make progress.
//
// This is only done if the system is ready so that PRE_BOOT_COMPLETED
// receivers don't get executed with timeouts. They're intended for
// one time heavy lifting after system upgrades and can take
// significant amounts of time.
int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
if (mService.mProcessesReady && r.dispatchTime > 0) {
long now = SystemClock.uptimeMillis();
if ((numReceivers > 0) &&
(now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {
Slog.w(TAG, "Hung broadcast ["
+ mQueueName + "] discarded after timeout failure:"
+ " now=" + now
+ " dispatchTime=" + r.dispatchTime
+ " startTime=" + r.receiverTime
+ " intent=" + r.intent
+ " numReceivers=" + numReceivers
+ " nextReceiver=" + r.nextReceiver
+ " state=" + r.state);
broadcastTimeoutLocked(false); // forcibly finish this broadcast
forceReceive = true;
r.state = BroadcastRecord.IDLE;
}这里面调用了broadcastTimeoutLocked来进行ANR埋雷，
这个broadcastTimeoutLocked埋雷后的处理，显然应当是在另外一个线程中，
查看其定义
final void setBroadcastTimeoutLocked(long timeoutTime) {
if (! mPendingBroadcastTimeoutMessage) {
Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
mHandler.sendMessageAtTime(msg, timeoutTime);
mPendingBroadcastTimeoutMessage = true;
}
}使用了mHandler相应的线程looper去处理，这个mHander是什么
是在这里定义的，继续查看传入的handler是什么，在AMS中，有
mHandlerThread = new ServiceThread(TAG, THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
mHandler = new MainHandler(mHandlerThread.getLooper());
mFgBroadcastQueue = new BroadcastQueue(this, mHandler, "foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler, "background", BROADCAST_BG_TIMEOUT, true);可以看到，是定义了一个ServiceThread，启动了一个线程looper，得证。