//Looper.java privatestaticvoidprepare(boolean quitAllowed){ if (sThreadLocal.get() != null) { thrownew RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper(quitAllowed)); }
privateLooper(boolean quitAllowed){ mQueue = new MessageQueue(quitAllowed); mThread = Thread.currentThread(); }
//ThreadLocal.java public T get(){ Thread t = Thread.currentThread(); ThreadLocalMap map = getMap(t); if (map != null) { ThreadLocalMap.Entry e = map.getEntry(this); if (e != null) { @SuppressWarnings("unchecked") T result = (T)e.value; return result; } } return setInitialValue(); }
//MessageQueue.java booleanenqueueMessage(Message msg, long when){ if (msg.target == null) { thrownew IllegalArgumentException("Message must have a target."); } if (msg.isInUse()) { thrownew IllegalStateException(msg + " This message is already in use."); } synchronized (this) { if (mQuitting) { msg.recycle(); returnfalse; } msg.markInUse(); msg.when = when; Message p = mMessages; boolean needWake; if (p == null || when == 0 || when < p.when) { // New head, wake up the event queue if blocked. msg.next = p; mMessages = msg; needWake = mBlocked; } else { // Inserted within the middle of the queue. Usually we don't have to wake // up the event queue unless there is a barrier at the head of the queue // and the message is the earliest asynchronous message in the queue. 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; // invariant: p == prev.next prev.next = msg; } // We can assume mPtr != 0 because mQuitting is false. if (needWake) { nativeWake(mPtr); } } returntrue; }
//MessageQueue.java Message next(){ //... int pendingIdleHandlerCount = -1; // -1 only during first iteration int nextPollTimeoutMillis = 0; for (;;) { if (nextPollTimeoutMillis != 0) { Binder.flushPendingCommands(); } //阻塞操作,等待 nextPollTimeoutMillis 时长或者消息队列被唤醒时会返回,是一个 native 方法 nativePollOnce(ptr, nextPollTimeoutMillis);
synchronized (this) { // Try to retrieve the next message. Return if found. finallong now = SystemClock.uptimeMillis(); Message prevMsg = null; Message msg = mMessages; //... 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 { // Got a message. mBlocked = false; if (prevMsg != null) { prevMsg.next = msg.next; } else { mMessages = msg.next; } msg.next = null; msg.markInUse(); return msg; } } else { // No more messages. nextPollTimeoutMillis = -1; }
// Process the quit message now that all pending messages have been handled. if (mQuitting) { dispose(); returnnull; }
// Run the idle handlers. // ... 关于 IdleHandler 可以在 [四、Handler 扩展] 中查看 } }
//MessageQueue.java Message next(){ //... int pendingIdleHandlerCount = -1; // -1 only during first iteration int nextPollTimeoutMillis = 0; for (;;) { //...
synchronized (this) { //...
// 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); }
// Run the idle handlers. // We only ever reach this code block during the first iteration. for (int i = 0; i < pendingIdleHandlerCount; i++) { final IdleHandler idler = mPendingIdleHandlers[i]; mPendingIdleHandlers[i] = null; // release the reference to the handler
if (!keep) { synchronized (this) { mIdleHandlers.remove(idler); } } }
// Reset the idle handler count to 0 so we do not run them again. pendingIdleHandlerCount = 0;
// While calling an idle handler, a new message could have been delivered // so go back and look again for a pending message without waiting. nextPollTimeoutMillis = 0; } }