Go併發控制之sync.WaitGroup

    WaitGroup 會將main goroutine阻塞直到全部的goroutine運行結束,從而達到併發控制的目的。使用方法很是簡單,真心佩服創造Golang的大師們!golang

 

type WaitGroup               //至關於一個箱子,將main goroutine 保護到裏面

func (*WaitGroup) Add   //調用一次爲箱子加一把鎖(固然,你願意也能夠多把)

func (*WaitGroup) Done  // 調用一次開一把鎖(only one!) 

func (*WaitGroup) Wait    //箱子的蓋子,沒鎖了自動打開

 

官網說明:一個WaitGroup鎖等待一個goroutines合集結束。main goroutine裏面調用Add方法設置須要等待的goroutines 數量,而後運行每個goroutine,而且當其結束時調用Done方法。同時,main goroutine 被鎖住直到全部的goroutines完成。併發

使用方法(官網Example):fetch

var wg sync.WaitGroup var urls = []string{ "http://www.golang.org/", "http://www.google.com/", "http://www.somestupidname.com/", } for _, url := range urls {   // Increment the WaitGroup counter.
  wg.Add(1)   // Launch a goroutine to fetch the URL.
  go func(url string) {     // Decrement the counter when the goroutine completes.
    defer wg.Done()     // Fetch the URL.
    http.Get(url)   }(url) } // Wait for all HTTP fetches to complete.
wg.Wait()

 

任何放在wg.Wait() 後面的語句阻塞,直到全部的goroutine返回:google

package main

import (
        "fmt"
        "net/http"
        "sync"
)

func main() {
        var wg sync.WaitGroup
        var urls = []string{
                "http://www.golang.org/",
                "http://www.google.com/",
                "http://www.somestupidname.com/",
        }
        for _, url := range urls {
                // Increment the WaitGroup counter.
                wg.Add(1)
                // Launch a goroutine to fetch the URL.
                go func(url string) {
                        // Decrement the counter when the goroutine completes.
                        defer wg.Done()
                        // Fetch the URL.
                        http.Get(url)
                        fmt.Println("我先幹活, 主程序等着我")
                }(url)
        }
        // Wait for all HTTP fetches to complete.
        wg.Wait()
        fmt.Println("應該最後纔出來")

}
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