go之select

package csp
 
import (
  "fmt"
  "testing"
  "time"
)
 
func service() string {
  time.Sleep(time.Millisecond * 50)
  return "Done"
}
 
//异步 chan在go中是一个通道有可读可写的chan,也存在只读只写的chan 异步返回
func AsyncService() chan string {
  //创建接受通道
  retCh := make(chan string, 1)
  go func() {
    ret := service()
    fmt.Println("returned result.")
    //chan放数据
    retCh <- ret
    fmt.Println("service exited.")
  }()
  return retCh
}
 
//多路选择、超时
func TestSelect(t *testing.T) {
  //使用select监听
  select {
  case ret := <-AsyncService():
    t.Log(ret)
  //  设置超时等待
  case <-time.After(time.Millisecond * 100):
    t.Error("time out")
 
  }
}

package csp
 
import (
  "fmt"
  "sync"
  "testing"
)
 
//生产者
func dataProducer(ch chan int, wg *sync.WaitGroup) {
  go func() {
    for i := 0; i < 10; i++ {
      //给通道添加数据
      ch <- i
    }
    //关闭channel,向关闭的channel发送数据，会导致panic
    close(ch)
    //ch <- -1 //panic: send on closed channel
    wg.Done()
  }()
}
 
//消费者
func dataReceiver(ch chan int, wg *sync.WaitGroup) {
  go func() {
    for {
      //从通道取数据,ok为bool值，true表示正常接收，false表示通道关闭
      //关闭通道，接收数据，返回零值
      if data, ok := <-ch; ok {
        fmt.Println(data)
      } else {
        break
      }
    }
    wg.Done()
  }()
}
 
func TestCloseChannel(t *testing.T) {
  var wg sync.WaitGroup
  //创建通道
  ch := make(chan int)
  wg.Add(1)
  //生成数据
  dataProducer(ch, &wg)
  wg.Add(1)
  //消费数据
  dataReceiver(ch, &wg)
  wg.Add(1)
  //消费数据
  dataReceiver(ch, &wg)
  wg.Wait()
}