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63 lines
1.6 KiB
63 lines
1.6 KiB
---
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Handler 的消息延时是怎么实现的？
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---
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1. 消息延时是做了什么特殊处理？
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2. 是发送延时了，还是消息延时处理了？
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3. 延时精度怎么样？
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```java
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boolean sendMessageDelayed(Message msg, long delayMillis){
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if(delayMillis<0){
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delayMillis=0;
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}
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return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);
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}
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public boolean sendMessageAtTime(Message msg, long uptimeMillis){
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MessageQueue queue = mQueue;
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return enqueueMessage(queue, msg, uptimeMillis);
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}
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boolean enqueueMessage(Message msg, long when){
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msg.when = when;
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Message p = mMessage, prew;
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if(p==null||when==0||when<p.when){
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msg.mext = p;
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mMessage = msg;
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}else{
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for(;;){
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prew = p;
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p = p.next;
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if(p==null||when<p.when){
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break;
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}
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}
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msg.next = p;
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prev.next = msg;
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}
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nativeWake(mPtr);
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}
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Message next(){
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for(int nextPollTimeoutMillis = 0;;){
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nativePollOnce(ptr, nextPollTimeoutMillis);
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final long now = SystemClock.uptimeMillis();
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Message msg = mMessages;
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if(msg != null){
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if(now<msg.when){
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nextPollTimeoutMillis = (int)Math.min(msg.when-now, Integer.MAX_VALUE);
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}else{
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mMessage = msg.next;
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msg.next = null;
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return msg;
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}
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}else{
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nextPollTimeoutMillis = -1;
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}
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}
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}
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```
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#### 总结
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1. 消息队列按消息触发时间排序
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2. 设置 epoll_wait 的超时时间，使其在特定时间唤醒
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3. 关于延时精度 |