Go语言等待组sync.WaitGrou的使用示例

package main
import (
    "fmt"
    "net/http"
    "sync"
)
func main() {
    // 声明一个等待组
    var wg sync.WaitGroup
    // 准备一系列的网站地址
    var urls = []string{
        "http://www.github.com/",
        "https://www.qiniu.com/",
        "https://www.golangtc.com/",
    }
    // 遍历这些地址
    for _, url := range urls {
        // 每一个任务开始时, 将等待组增加1
        wg.Add(1)
        // 开启一个并发
        go func(url string) {
            // 使用defer, 表示函数完成时将等待组值减1
            defer wg.Done()
            // 使用http访问提供的地址
            _, err := http.Get(url)
            // 访问完成后, 打印地址和可能发生的错误
            fmt.Println(url, err)
            // 通过参数传递url地址
        }(url)
    }
    // 等待所有的任务完成
    wg.Wait()
    fmt.Println("over")
}

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()

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

const (
   num = 10000000
)

func main() {
   TestFunc("testchan", TestChan)
}

func TestFunc(name string, f func()) {
   st := time.Now().UnixNano()
   f()
   fmt.Printf("task %s cost %d \r\n", name, (time.Now().UnixNano()-st)/int64(time.Millisecond))
}

func TestChan() {
   var wg sync.WaitGroup
   c := make(chan string)
   wg.Add(1)

   go func() {
      for _ = range c {
      }
      wg.Done()
   }()

   for i := 0; i < num; i++ {
      c <- "123"
   }
   close(c)
   wg.Wait()
}