Go 语言入门之Go 计时器介绍

引言

​Ticker​​time​​NewTicker()​​chan​​bool​

Go 的计时器

Go 提供了非常简单的语法来实现一个计时器，定时器的结构体定义：

type Ticker struct {
C <-chan Time // 抛出来的channel，给上层系统使用，实现计时
r runtimeTimer // 给系统管理使用的定时器，系统通过该字段确定定时器是否到时，如果到时，调用对应的函数向C中推送当前时间。
}

Ticker对外仅暴露一个 channel，指定的时间到来时就往该 channel 中写入系统时间，也即一个事件。

Ticker 的使用方式也很简单，代码如下：

import time
TimeTicker := time.NewTicker(1 * time.Second)
TimeTicker.Stop()

​time​​time​​NewTicker()​​1*time.Second​​1​​2*time.Millisecond​​NewTicker​​TimeTicker.Stop()​​TimeTicker.stop()​

我们可以每隔一秒输出一个结果，比如实现一个倒数 10 个数的功能：

package main
import (
"fmt"
"time"
)
func main() {
TimeTicker := time.NewTicker(1 * time.Second)
i := 10
for {
<-TimeTicker.C
fmt.Println("i = ", i)
i--
if i == 0 {
TimeTicker.Stop()
break
}
}
}

然后执行该程序：

$ go run main.go
i = 10
i = 9
i = 8
i = 7
i = 6
i = 5
i = 4
i = 3
i = 2
i = 1

Ticker 计时器是如何工作的？

​NewTicker​​NewTimer​​channel​​channel​​sendTime​​Ticker​

func NewTicker(d Duration) *Ticker {
if d <= 0 {
panic(errors.New("non-positive interval for NewTicker"))
}
// Give the channel a 1-element time buffer.
// If the client falls behind while reading, we drop ticks
// on the floor until the client catches up.
c := make(chan Time, 1)
t := &Ticker{
C: c,
r: runtimeTimer{
when: when(d),
period: int64(d),
f: sendTime,
arg: c,
},
}
startTimer(&t.r)
return t
}

NewTicker()只是构造了一个Ticker，然后把Ticker.r通过startTimer()交给系统协程维护。

period

​sendTime()​

func sendTime(c interface{}, seq uintptr) {
select {
case c.(chan Time) <- Now():
default:
}
}

​sendTime​

停止Ticker:

Ticker

函数主要实现如下：

func (t *Ticker) Stop() {
stopTimer(&t.r)
}

​stopTicker()​

Ticker 使用方式

例子一：

package main
import (
"fmt"
"time"
)
func main() {
TimeTicker := time.NewTicker(3 * time.Second)
tickerChannel := make(chan bool)
go func() {
for {
select {
case timeticker := <-TimeTicker.C:
fmt.Println("The time for current is : ", timeticker)
case <-tickerChannel:
return
}
}
}()
time.Sleep(6 * time.Second)
TimeTicker.Stop()
tickerChannel <- true
fmt.Println("Time for running ticker is completed")
}

运行该代码：

$ go run main.go
The time for current is : 2022-04-29 22:37:13.93862 +0800 CST m=+3.000267823
The time for current is : 2022-04-29 22:37:16.939081 +0800 CST m=+6.000707515
Time for running ticker is completed

例子二：

package main
import (
"fmt"
"time"
)
func main() {
tm := time.Millisecond
tickerTicker := time.NewTicker(400 * tm)
tickerChaneel := make(chan bool)
go func() {
for {
select {
case <-tickerChaneel:
return
case tmtr := <-tickerTicker.C:
fmt.Println("Ticker time at current is", tmtr)
}
}
}()
time.Sleep(1400 * time.Millisecond)
tickerTicker.Stop()
tickerChaneel <- true
fmt.Println("Ticker has stopped now")
}

运行该代码：

$ go run main.go
Ticker time at current is 2022-04-29 22:39:51.13057 +0800 CST m=+0.400159916
Ticker time at current is 2022-04-29 22:39:51.531516 +0800 CST m=+0.801102997
Ticker time at current is 2022-04-29 22:39:51.931238 +0800 CST m=+1.200822301
Ticker has stopped now

总结

​Ticker​​ticker​