needWake = mBlocked && p.target == null && msg.isAsynchronous();
Message prev;
for (;;) {
prev = p;
p = p.next;
if (p == null || when < p.when) {
break;
}
if (needWake && p.isAsynchronous()) {
needWake = false;
}
}
msg.next = p;
prev.next = msg;
}
if (needWake) {
nativeWake(mPtr);
}
}
returntrue;
}
Message next() {
//与native方法相关,当mPtr为0时返回null,退出消息循环finallong ptr = mPtr;
if (ptr == 0) {
returnnull;
}
int pendingIdleHandlerCount = -1;
//0不进入睡眠,-1进入睡眠 int nextPollTimeoutMillis = 0;
for (;;) {
if (nextPollTimeoutMillis != 0) {
//处理当前线程中待处理的Binder进程间通信请求 Binder.flushPendingCommands();
}
//native方法,nextPollTimeoutMillis为-1时进入睡眠状态
//阻塞方法，主要是通过native层的epoll监听文件描述符的写入事件来实现的。
//如果nextPollTimeoutMillis=-1，一直阻塞不会超时。
//如果nextPollTimeoutMillis=0，不会阻塞，立即返回。
//如果nextPollTimeoutMillis>0，最长阻塞nextPollTimeoutMillis毫秒(超时)，如果期间有程序唤醒会立即返回 nativePollOnce(ptr, nextPollTimeoutMillis);
synchronized (this) {
finallong now = SystemClock.uptimeMillis();
Message prevMsg = null;
Message msg = mMessages;
if (msg != null && msg.target == null) {
do {
prevMsg = msg;
msg = msg.next;
} while (msg != null && !msg.isAsynchronous());
}
if (msg != null) {
if (now < msg.when) {
// Next message is not ready. Set a timeout to wake up when it is ready.
nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
} else {
//正常取出消息，设置mBlocked = false代表目前没有阻塞
mBlocked = false;
if (prevMsg != null) {
prevMsg.next = msg.next;
} else {
mMessages = msg.next;
}
msg.next = null;
msg.markInUse();
return msg;
}
} else {
// No more messages.更新到睡眠状态
nextPollTimeoutMillis = -1;
}
// Process the quit message now that all pending messages have been handled.if (mQuitting) {
dispose();
returnnull;
}
// If first time idle, then get the number of idlers to run.
// Idle handles only run if the queue is empty or if the first message
// in the queue (possibly a barrier) is due to be handled in the future.if (pendingIdleHandlerCount < 0
&& (mMessages == null || now < mMessages.when)) {
pendingIdleHandlerCount = mIdleHandlers.size();
}
if (pendingIdleHandlerCount <= 0) {
// No idle handlers to run. Loop and wait some more.
mBlocked = true;
continue;
}
if (mPendingIdleHandlers == null) {
mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
}
mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
}
}
//非睡眠状态下处理IdleHandler接口 for (int i = 0; i < pendingIdleHandlerCount; i++) {
final IdleHandler idler = mPendingIdleHandlers[i];
// release the reference to the handler
mPendingIdleHandlers[i] = null;
boolean keep = false;
try {
keep = idler.queueIdle();
} catch (Throwable t) {
Log.wtf(TAG, "IdleHandler threw exception", t);
}
if (!keep) {
synchronized (this) {
mIdleHandlers.remove(idler);
}
}
}
pendingIdleHandlerCount = 0;
nextPollTimeoutMillis = 0;
}
}
Handler.class源码分析：
/*
*通过handler类向线程的消息队列发送消息，
*每个Handler对象中都有一个Looper对象和MessageQueue对象
*/public Handler(Callback callback, boolean async) {
if (FIND_POTENTIAL_LEAKS) {
final Class<? extends Handler> klass = getClass();
if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isL