Golang

【Golang】使用 - 限时调用一个函数（超时退出）

Posted by 西维蜀黍 on 2020-11-24, Last Modified on 2021-09-21

使用 time.After

package main

import (
   "fmt"
   "time"
)

func main() {

   c1 := make(chan string, 1)
   go func() {
      fmt.Printf("before sleep: %v\n", time.Now())
      time.Sleep(2 * time.Second)
      c1 <- "result 1"
      // Never go to here
      fmt.Printf("after sleep: %v\n", time.Now())
   }()

   fmt.Printf("before select: %v\n", time.Now())
   select {
   case res := <-c1:
      fmt.Println(res)
   case <-time.After(1 * time.Second):
      fmt.Println("timeout 1")
   }
   fmt.Printf("after select: %v\n", time.Now())
}

Output:

before select: 2020-11-24 22:57:40.129712 +0800 +08 m=+0.000122644
before sleep: 2020-11-24 22:57:40.129721 +0800 +08 m=+0.000131671
timeout 1
after select: 2020-11-24 22:57:41.13308 +0800 +08 m=+1.003459705

For our example, suppose we’re executing an external call that returns its result on a channel c1 after 2s. Note that the channel is buffered, so the send in the goroutine is nonblocking. This is a common pattern to prevent goroutine leaks in case the channel is never read.

Here’s the select implementing a timeout. res := <-c1 awaits the result and <-time.After awaits a value to be sent after the timeout of 1s. Since select proceeds with the first receive that’s ready, we’ll take the timeout case as the operation (we use hardcode time.Sleep(2 * time.Second) here) takes more than the allowed 1s.

同时考虑 context deadline

package main

import (
	"context"
	"fmt"
	"time"
)

func main() {
	AsyncCall()
}

func AsyncCall() {
	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(time.Millisecond*800))
	defer cancel()
	go func(ctx context.Context) {
		fmt.Print("sss")
	}(ctx)

	select {
	case <-ctx.Done():
		fmt.Println("call successfully!!!")
		return
	case <-time.After(time.Duration(time.Millisecond * 900)):
		fmt.Println("timeout!!!")
		return
	}
}

说明

1、通过context的WithTimeout设置一个有效时间为800毫秒的context。

2、该context会在耗尽800毫秒后或者方法执行完成后结束，结束的时候会向通道ctx.Done发送信号。

3、有人可能要问，你这里已经设置了context的有效时间，为什么还要加上这个time.After呢？

这是因为该方法内的context是自己申明的，可以手动设置对应的超时时间，但是在大多数场景，这里的ctx是从上游一直传递过来的，对于上游传递过来的context还剩多少时间，我们是不知道的，所以这时候通过time.After设置一个自己预期的超时时间就很有必要了。

4、注意，这里要记得调用cancel()，不然即使提前执行完了，还要傻傻等到800毫秒后context才会被释放。

Reference

FEATURED TAGS
algorithm algorithmproblem architecturalpattern architecture aws c# cachesystem codis compile concurrentcontrol database dataformat datastructure debug design designpattern distributedsystem django docker domain engineering freebsd git golang grafana hackintosh hadoop hardware hexo http hugo ios iot java javaee javascript kafka kubernetes linux linuxcommand linuxio lock macos markdown microservices mysql nas network networkprogramming nginx node.js npm oop openwrt operatingsystem padavan performance programming prometheus protobuf python redis router security shell software testing spring sql systemdesign truenas ubuntu vmware vpn windows wmware wordpress xml zookeeper
FRIENDS

TOC