go - 如果 Ticker 已经在运行，则不应执行

Question

我有一些必须定期运行的功能。我为此使用了自动收报机。但是如果代码已经在运行，并且时间间隔再次过去，它不应该再次执行。

package main

import (
    "fmt"
    "time"
)

func main() {
    ticker := time.NewTicker(3*time.Second)
    flag := 0
    defer ticker.Stop()
    for {
        select {
        case t := <-ticker.C:
            flag = flag + 1
            if (flag % 2 ==0 ) {
                time.Sleep(time.Second*4)
            }   
            fmt.Println("Current time: ", t)
        }
    }
}

https://play.golang.org/p/2xV2MYInn4I

在 Playground 上，自动收报机每 3 秒打印一次，但每次自动收报机的偶数转一圈，作业所花费的时间都比间隔时间长。我希望它不会运行并放弃那些滴答声。

我该怎么做？

Answer 1

在同一个 goroutine 中休眠只会延迟执行。同时，ticker 在一个单独的 goroutine 中运行。因此，即使您使用全局变量来维持执行状态 - 它也不会为您提供所需的 sleep 结果。然而，在一个单独的 goroutine 中迁移整个“ sleep ”会产生:

package main

import (
    "fmt"
    "time"
)

type Tick struct {
    ticker *time.Ticker
    executing bool
}

func somethingYouWantToDo(tick *Tick, flag *int, t time.Time) {
    if tick.executing {
        return
    }

    tick.executing = true

    *flag = *flag + 1

    if (*flag % 2 ==0 ) {
                time.Sleep(time.Second*4)
    }   
        fmt.Println("Current time: ", t)
    tick.executing = false
}

func main() {
    tick := &Tick{
        ticker: time.NewTicker(3*time.Second),
    }
    flag := 0
    defer tick.ticker.Stop()
    for {
        select {
        case t := <-tick.ticker.C:
            go somethingYouWantToDo(tick, &flag, t)
        }
    }
}
// output
// Current time:  2009-11-10 23:00:03 +0000 UTC m=+3.000000001
// Current time:  2009-11-10 23:00:06 +0000 UTC m=+6.000000001
// Current time:  2009-11-10 23:00:12 +0000 UTC m=+12.000000001
// Current time:  2009-11-10 23:00:15 +0000 UTC m=+15.000000001
// Current time:  2009-11-10 23:00:21 +0000 UTC m=+21.000000001
// Current time:  2009-11-10 23:00:24 +0000 UTC m=+24.000000001
// Current time:  2009-11-10 23:00:30 +0000 UTC m=+30.000000001
// Current time:  2009-11-10 23:00:33 +0000 UTC m=+33.000000001
// Current time:  2009-11-10 23:00:39 +0000 UTC m=+39.000000001
// Current time:  2009-11-10 23:00:42 +0000 UTC m=+42.000000001
// Current time:  2009-11-10 23:00:48 +0000 UTC m=+48.000000001
// Current time:  2009-11-10 23:00:51 +0000 UTC m=+51.000000001
// Current time:  2009-11-10 23:00:57 +0000 UTC m=+57.000000001
// Current time:  2009-11-10 23:01:00 +0000 UTC m=+60.000000001
// Current time:  2009-11-10 23:01:06 +0000 UTC m=+66.000000001
// Current time:  2009-11-10 23:01:09 +0000 UTC m=+69.000000001

Try it on the playground