Android(安卓)启动优化-IdleHandler
16lz
2022-08-09
Android 启动优化-IdleHandler
- 1、IdleHandler 的简单使用
- 2、系统使用的案例
- 3、IdleHandler的源码实现
1、IdleHandler 的简单使用
在Android中，当消息队列没有可处理的消息的时候，就是消息队列时空的，或者消息队列里的消息还没到可触发的时间，就会执行IdleHandler。
Looper.myQueue().addIdleHandler(new IdleHandler() { @Override public boolean queueIdle() { //在这里可以加载一些业务没有这么快涉及三方的sdk return false; //false 只会触发一次 ，true空闲是都会返回 } });2、系统使用的案例
我们都知道，Android系统开启应用进程的时候，会调到ActivityThread类中的main()方法，在ActivityThread类中会用到，第一次idler的时候，调了一次GC。
void scheduleGcIdler() { if (!mGcIdlerScheduled) { mGcIdlerScheduled = true; Looper.myQueue().addIdleHandler(mGcIdler); } mH.removeMessages(H.GC_WHEN_IDLE); } final class GcIdler implements MessageQueue.IdleHandler { @Override public final boolean queueIdle() { doGcIfNeeded(); return false; } }在Instrumentation 类里边。
public void waitForIdle(Runnable recipient) { mMessageQueue.addIdleHandler(new Idler(recipient)); mThread.getHandler().post(new EmptyRunnable()); } private static final class Idler implements MessageQueue.IdleHandler { private final Runnable mCallback; private boolean mIdle; public Idler(Runnable callback) { mCallback = callback; mIdle = false; } public final boolean queueIdle() { if (mCallback != null) { mCallback.run(); } synchronized (this) { mIdle = true; notifyAll(); } return false; } public void waitForIdle() { synchronized (this) { while (!mIdle) { try { wait(); } catch (InterruptedException e) { } } } } }3、IdleHandler的源码实现
当我们调用 Looper.myQueue().addIdleHandler(new IdleHandler()）的时候，会将当前的idle加入IdleHandler[] mPendingIdleHandlers，当消息队列没有可执行消息时，进入阻塞，就有回调 idler.queueIdle()
Message next() { // Return here if the message loop has already quit and been disposed. // This can happen if the application tries to restart a looper after quit // which is not supported. final long ptr = mPtr; if (ptr == 0) { return null; } int pendingIdleHandlerCount = -1; // -1 only during first iteration int nextPollTimeoutMillis = 0; for (;;) { if (nextPollTimeoutMillis != 0) { Binder.flushPendingCommands(); } nativePollOnce(ptr, nextPollTimeoutMillis); synchronized (this) { // Try to retrieve the next message. Return if found. final long now = SystemClock.uptimeMillis(); Message prevMsg = null; Message msg = mMessages; if (msg != null && msg.target == null) { // Stalled by a barrier. Find the next asynchronous message in the queue. 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 { // Got a message. mBlocked = false; if (prevMsg != null) { prevMsg.next = msg.next; } else { mMessages = msg.next; } msg.next = null; if (DEBUG) Log.v(TAG, "Returning message: " + msg); 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(); return null; } // 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 boolean keep = false; try { keep = idler.queueIdle(); } catch (Throwable t) { Log.wtf(TAG, "IdleHandler threw exception", t); } 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; } }.
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