Go语言WaitGroup

冷不防 2023-10-03 10:08 1阅读 0赞

# `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

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

> 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

type WaitGroup
      func (wg *WaitGroup) Add(delta int)
      func (wg *WaitGroup) Done()
      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

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()
    }