一.WaitGroup简介

  • Golang中sync包提供了基本同步基元,如互斥锁等.除了Once和WaitGroup类型, 大部分都只适用于低水平程序线程,高水平同步线程使用channel通信更好一些
  • WaitGroup直译为等待组,其实就是计数器,只要计数器中有内容将一直阻塞

  • 在Golang中WaitGroup存在于sync包中,在sync包中类型都是不应该被拷贝的.源码定义如下

    1. // A WaitGroup waits for a collection of goroutines to finish.
    2. // The main goroutine calls Add to set the number of
    3. // goroutines to wait for. Then each of the goroutines
    4. // runs and calls Done when finished. At the same time,
    5. // Wait can be used to block until all goroutines have finished.
    6. //
    7. // A WaitGroup must not be copied after first use.
    8. type WaitGroup struct {
    9.   noCopy noCopy
    11.   // 64-bit value: high 32 bits are counter, low 32 bits are waiter count.
    12.   // 64-bit atomic operations require 64-bit alignment, but 32-bit
    13.   // compilers do not ensure it. So we allocate 12 bytes and then use
    14.   // the aligned 8 bytes in them as state.
    15.   state1 [12]byte
    16.   sema   uint32
    17. }

  • Go语言标准库中WaitGroup只有三个方法

    • Add(delta int)表示向内部计数器添加增量(delta),其中参数delta可以是负数
    • Done()表示减少WaitGroup计数器的值,应当在程序最后执行.相当于Add(-1)
    • Wait()表示阻塞直到WaitGroup计数器为0
      1. type WaitGroup
      2. func (wg *WaitGroup) Add(delta int)
      3. func (wg *WaitGroup) Done()
      4. func (wg *WaitGroup) Wait()

二.代码示例

  • 使用WaitGroup可以有效解决goroutine未执行完成主协程执行完成,导致程序结束,goroutine未执行问题 ```go package main

import ( “fmt” “sync” )

var wg sync.WaitGroup

func main() {

for i := 1; i <= 3; i++ { wg.Add(1) go demo(i) } //阻塞,知道WaitGroup队列中所有任务执行结束时自动解除阻塞 fmt.Println(“开始阻塞”) wg.Wait() fmt.Println(“任务执行结束,解除阻塞”)

}

func demo(index int) { for i := 1; i <= 5; i++ { fmt.Printf(“第%d次执行,i的值为:%d\n”, index, i) } wg.Done() } ```