golang

package main
import (
 "fmt"   
 "sync"
)
 
func main() {
   var once sync.Once
   onceBody := func() {
      fmt.Println("Only once")
   }
   done := make(chan bool)

   // 创建 10 个 goroutine，但是 onceBody 只会执行 1 次
   for i := 0; i < 10; i++ {
      go func() {
         once.Do(onceBody)
         done <- true
      }()
   }

   // 等待 10 个 goroutine 结束
   for i := 0; i < 10; i++ {
      <-done
   }
}

输出结果：

js
Only once

如何通过select 和ticker配合定时执行任务

js
package main

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

func runTask(ctx context.Context, wg *sync.WaitGroup, name string, interval time.Duration) {
	defer wg.Done()
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		select {
		case <-ticker.C:
			fmt.Println("run task", name, time.Now())
		case <-ctx.Done():
			fmt.Println("stop task", name)
			return
		}
	}
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	var wg sync.WaitGroup

	wg.Add(2)
	go runTask(ctx, &wg, "task1", time.Second*3)
	go runTask(ctx, &wg, "task2", time.Second*9)
	time.Sleep(time.Second * 20)
	cancel()
	wg.Wait()
	fmt.Println("exit")
}