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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<!-- 2021-01-23 Sat 18:03 -->
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<title>go中的定时器timer</title>
<meta name="generator" content="Org mode" />
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<div id="org-div-home-and-up">
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<h1 class="title">go中的定时器timer</h1>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#orgc66beaf">1. 使用方法</a></li>
<li><a href="#org56e722c">2. 内部实现</a></li>
<li><a href="#orgc13592d">3. 其他实现方法</a></li>
</ul>
</div>
</div>
<div id="outline-container-orgc66beaf" class="outline-2">
<h2 id="orgc66beaf"><span class="section-number-2">1</span> 使用方法</h2>
<div class="outline-text-2" id="text-1">
<p>
golang中定时器的使用接口在time包中，其中最主要两个接口是time.After跟,time.AfterFunc其中第一个After接口返回一个chan Time, 当时间到时可以读出Timer, AfterFunc接受一个方法，当时间到时执行这个方法。
</p>
<div class="org-src-container">
<pre class="src src-go"><span style="color: #89DDFF;">package</span> main
<span style="color: #89DDFF;">import</span> (
<span style="color: #c3e88d;">"time"</span>
<span style="color: #c3e88d;">"fmt"</span>
)
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">main</span>() {
<span style="color: #ffcb6b;">a</span> := time.<span style="color: #82aaff;">After</span>(2 * time.Second)
<- a
fmt.<span style="color: #82aaff;">Println</span>(<span style="color: #c3e88d;">"timer receive"</span>)
time.<span style="color: #82aaff;">AfterFunc</span>(2 * time.Second, <span style="color: #89DDFF;">func</span>(){
fmt.<span style="color: #82aaff;">Println</span>(<span style="color: #c3e88d;">"timer receive"</span>)
})
}
</pre>
</div>
<p>
After其实跟AfterFunc差不多，只不过其中的func参数是先通道中写数据
</p>
</div>
</div>
<div id="outline-container-org56e722c" class="outline-2">
<h2 id="org56e722c"><span class="section-number-2">2</span> 内部实现</h2>
<div class="outline-text-2" id="text-2">
<p>
由于After跟AfterFunc差不多，这里主要看看AfterFunc的实现
</p>
<div class="org-src-container">
<pre class="src src-go"> <span style="color: #676E95;">//</span><span style="color: #676E95;">time/sleep.go</span>
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">AfterFunc</span>(<span style="color: #ffcb6b;">d</span> <span style="color: #c792ea;">Duration</span>, <span style="color: #ffcb6b;">f</span> <span style="color: #89DDFF;">func</span>()) *<span style="color: #c792ea;">Timer</span> {
<span style="color: #ffcb6b;">t</span> := &<span style="color: #c792ea;">Timer</span>{
<span style="color: #f78c6c;">r</span>: <span style="color: #c792ea;">runtimeTimer</span>{
<span style="color: #f78c6c;">when</span>: <span style="color: #82aaff;">when</span>(d),
<span style="color: #f78c6c;">f</span>: goFunc,
<span style="color: #f78c6c;">arg</span>: f,
},
}
<span style="color: #82aaff;">startTimer</span>(&t.r)
<span style="color: #89DDFF;">return</span> t
}
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">goFunc</span>(<span style="color: #ffcb6b;">arg</span> <span style="color: #89DDFF;">interface</span>{}, <span style="color: #ffcb6b;">seq</span> <span style="color: #c792ea;">uintptr</span>) {
<span style="color: #89DDFF;">go</span> arg.(<span style="color: #89DDFF;">func</span>())()
}
</pre>
</div>
<p>
AfterFunc很简单，就是把参数封装为runtimeTimer,然后启动timer(把timer添加到队列中), 这部分代码在runtime/time.go中,注意这里goFunc新启动了一个goroutine来执行用户的任务,这样用户的func就不会堵塞timer
</p>
<div class="org-src-container">
<pre class="src src-go"><span style="color: #676E95;">//</span><span style="color: #676E95;">runtime/time.go</span>
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">startTimer</span>(<span style="color: #ffcb6b;">t</span> *<span style="color: #c792ea;">timer</span>) {
<span style="color: #89DDFF;">if</span> raceenabled {
<span style="color: #82aaff;">racerelease</span>(unsafe.<span style="color: #82aaff;">Pointer</span>(t))
}
<span style="color: #82aaff;">addtimer</span>(t)
}
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">addtimer</span>(<span style="color: #ffcb6b;">t</span> *<span style="color: #c792ea;">timer</span>) {
<span style="color: #82aaff;">lock</span>(&timers.lock)
<span style="color: #82aaff;">addtimerLocked</span>(t)
<span style="color: #82aaff;">unlock</span>(&timers.lock)
}
<span style="color: #676E95;">// </span><span style="color: #676E95;">Add a timer to the heap and start or kick the timer proc.</span>
<span style="color: #676E95;">// </span><span style="color: #676E95;">If the new timer is earlier than any of the others.</span>
<span style="color: #676E95;">// </span><span style="color: #676E95;">Timers are locked.</span>
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">addtimerLocked</span>(<span style="color: #ffcb6b;">t</span> *<span style="color: #c792ea;">timer</span>) {
<span style="color: #676E95;">// </span><span style="color: #676E95;">when must never be negative; otherwise timerproc will overflow</span>
<span style="color: #676E95;">// </span><span style="color: #676E95;">during its delta calculation and never expire other runtime·timers.</span>
<span style="color: #89DDFF;">if</span> t.when < 0 {
t.when = 1<<63 - 1
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">添加time到全局timer</span>
t.i = <span style="color: #82aaff;">len</span>(timers.t)
timers.t = <span style="color: #82aaff;">append</span>(timers.t, t)
<span style="color: #676E95;">//</span><span style="color: #676E95;">使用最小堆算法维护timer队列</span>
<span style="color: #82aaff;">siftupTimer</span>(t.i)
<span style="color: #676E95;">//</span><span style="color: #676E95;">如果是第一个</span>
<span style="color: #89DDFF;">if</span> t.i == 0 {
<span style="color: #676E95;">// </span><span style="color: #676E95;">siftup moved to top: new earliest deadline.</span>
<span style="color: #676E95;">//</span><span style="color: #676E95;">如果在sleep中, 唤醒</span>
<span style="color: #89DDFF;">if</span> timers.sleeping {
timers.sleeping = <span style="color: #f78c6c;">false</span>
<span style="color: #82aaff;">notewakeup</span>(&timers.waitnote)
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">如果在调度中, 等待</span>
<span style="color: #89DDFF;">if</span> timers.rescheduling {
timers.rescheduling = <span style="color: #f78c6c;">false</span>
<span style="color: #82aaff;">goready</span>(timers.gp, 0)
}
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">如果timer还没创建,则创建</span>
<span style="color: #89DDFF;">if</span> <span style="color: #89DDFF; font-weight: bold;">!</span>timers.created {
timers.created = <span style="color: #f78c6c;">true</span>
<span style="color: #89DDFF;">go</span> <span style="color: #82aaff;">timerproc</span>()
}
}
<span style="color: #89DDFF;">func</span> <span style="color: #82aaff;">timerproc</span>() {
timers.gp = <span style="color: #82aaff;">getg</span>()
<span style="color: #89DDFF;">for</span> {
<span style="color: #82aaff;">lock</span>(&timers.lock)
timers.sleeping = <span style="color: #f78c6c;">false</span>
<span style="color: #ffcb6b;">now</span> := <span style="color: #82aaff;">nanotime</span>()
<span style="color: #ffcb6b;">delta</span> := <span style="color: #82aaff;">int64</span>(-1)
<span style="color: #89DDFF;">for</span> {
<span style="color: #89DDFF;">if</span> <span style="color: #82aaff;">len</span>(timers.t) == 0 {
delta = -1
<span style="color: #89DDFF;">break</span>
}
<span style="color: #ffcb6b;">t</span> := timers.t[0]
<span style="color: #676E95;">//</span><span style="color: #676E95;">得到剩余时间, 还没到时间就sleep</span>
delta = t.when - now
<span style="color: #89DDFF;">if</span> delta > 0 {
<span style="color: #89DDFF;">break</span>
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">如果是周期性的就算下一次时间</span>
<span style="color: #89DDFF;">if</span> t.period > 0 {
<span style="color: #676E95;">// </span><span style="color: #676E95;">leave in heap but adjust next time to fire</span>
t.when += t.period * (1 + -delta/t.period)
<span style="color: #676E95;">//</span><span style="color: #676E95;">最小堆下沉</span>
<span style="color: #82aaff;">siftdownTimer</span>(0)
} <span style="color: #89DDFF;">else</span> {
<span style="color: #676E95;">// </span><span style="color: #676E95;">remove from heap</span>
<span style="color: #676E95;">//</span><span style="color: #676E95;">删除将要执行的timer,(最小堆算法)</span>
<span style="color: #ffcb6b;">last</span> := <span style="color: #82aaff;">len</span>(timers.t) - 1
<span style="color: #89DDFF;">if</span> last > 0 {
timers.t[0] = timers.t[last]
timers.t[0].i = 0
}
timers.t[last] = <span style="color: #f78c6c;">nil</span>
timers.t = timers.t[:last]
<span style="color: #89DDFF;">if</span> last > 0 {
<span style="color: #82aaff;">siftdownTimer</span>(0)
}
t.i = -1 <span style="color: #676E95;">// </span><span style="color: #676E95;">mark as removed</span>
}
<span style="color: #ffcb6b;">f</span> := t.f
<span style="color: #ffcb6b;">arg</span> := t.arg
<span style="color: #ffcb6b;">seq</span> := t.seq
<span style="color: #82aaff;">unlock</span>(&timers.lock)
<span style="color: #89DDFF;">if</span> raceenabled {
<span style="color: #82aaff;">raceacquire</span>(unsafe.<span style="color: #82aaff;">Pointer</span>(t))
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">执行函数调用函数</span>
<span style="color: #82aaff;">f</span>(arg, seq)
<span style="color: #82aaff;">lock</span>(&timers.lock)
}
<span style="color: #676E95;">//</span><span style="color: #676E95;">继续下一个,因为可能下一个timer也到时间了</span>
<span style="color: #89DDFF;">if</span> delta < 0 || faketime > 0 {
<span style="color: #676E95;">// </span><span style="color: #676E95;">No timers left - put goroutine to sleep.</span>
timers.rescheduling = <span style="color: #f78c6c;">true</span>
<span style="color: #82aaff;">goparkunlock</span>(&timers.lock, <span style="color: #c3e88d;">"timer goroutine (idle)"</span>, traceEvGoBlock, 1)
<span style="color: #89DDFF;">continue</span>
}
<span style="color: #676E95;">// </span><span style="color: #676E95;">At least one timer pending. Sleep until then.</span>
timers.sleeping = <span style="color: #f78c6c;">true</span>
<span style="color: #82aaff;">noteclear</span>(&timers.waitnote)
<span style="color: #82aaff;">unlock</span>(&timers.lock)
<span style="color: #676E95;">//</span><span style="color: #676E95;">没到时间,睡眠delta时间</span>
<span style="color: #82aaff;">notetsleepg</span>(&timers.waitnote, delta)
}
}
</pre>
</div>
</div>
</div>
<div id="outline-container-orgc13592d" class="outline-2">
<h2 id="orgc13592d"><span class="section-number-2">3</span> 其他实现方法</h2>
<div class="outline-text-2" id="text-3">
<p>
以前也看过erlang的timer的实现，不过erlang的实现是使用时间轮的方式，不同的时间挂在不同的时间刻度上，而golang使用的最小堆维护的一个timer队列。总的来说golang的实现方式比较简单，erlang的方式比较复杂，但是erlang在支持比较大量的timer情况下比较好,效率比较高。而go比较费时，每次操作最坏情况下都是logn（n为时间队列长度）.
</p>
</div>
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