[go] chan close

close chan

• close由发送端调用，在收到最后一个发送值后关闭管道（It should be executed only by the sender, never the receiver, and has the effect of shutting down the channel after the last sent value is received）
• close管道后，所有从管道的读取会获得元素对应类型的零值（any receive from c will succeed without blocking, returning the zero value for the channel element.）

package main

import (
    "fmt"
    "time"
)

func main() {
    stop := make(chan struct{})

    go func() {
        select {
        case _, ok := <-stop:
            fmt.Println("stop 01: ", ok)
        }
    }()

    go func() {
        select {
        case _, ok := <-stop:
            fmt.Println("stop 02: ", ok)
        }
    }()

    stop <- struct{}{}
    close(stop)

    time.Sleep(time.Second * 2)

    _, ok := <-stop
    fmt.Println("stop chan: ", ok)
}

stop 02: true
stop 01: false
stop chan: false

结论：chan中发送的值被第二个协程读取，主协程和第一个协程的读取都返回了bool的零值（false）

• 不允许给已关闭的chan发送值，见下例：

  package main
  
  func main() {
    stop := make(chan struct{})
    close(stop)
  
    stop <- struct{}{}
  }

  panic: send on closed channel

• 给chan发送值，只能被读取一次

  package main
  
  import (
    "fmt"
    "time"
  )
  
  func main() {
    stop := make(chan struct{})
  
    go func() {
        select {
        case _, ok := <-stop:
            //stop = nil
            fmt.Println("stop 01: ", ok)
        }
    }()
  
    go func() {
        select {
        case _, ok := <-stop:
            fmt.Println("stop 02: ", ok)
        }
    }()
  
    stop <- struct{}{}
  
    time.Sleep(time.Second * 2)
  }

  stop 02: true

这里因为只给chan发送了一个值，所以只会退出一个协程（随机性）。