golang channel 总结

1、未初始化的channel读，阻塞

package main import ( "fmt" "time" ) func main() { var ch chan int go check(ch) fmt.Println("main runtime end") time.Sleep(time.Second * 1000) } func check(ch chan int) { select { case i := <-ch: fmt.Println("read ch data=", i) } fmt.Println("check runtime exit") } 

2、未初始化的channel写，阻塞

package main import ( "fmt" "time" ) func main() { go func() { for { time.Sleep(time.Second * 1) } }() var ch chan int go check(ch) time.Sleep(time.Second * 1) fmt.Println("xxxxxxx") <-ch fmt.Println("main runtime end") time.Sleep(time.Second * 1000) } func check(ch chan int) { defer func() { if r := recover(); r != nil { fmt.Println("recover ", r) } }() ch <- 1 fmt.Println("check runtime exit") } 

3、向已关闭的channel读，返回默认值和false

package main import ( "fmt" "time" ) func main() { var ch chan int ch = make(chan int) go check(ch) fmt.Println("main runtime end") close(ch) time.Sleep(time.Second * 1000) } func check(ch chan int) { select { case i, k := <-ch: fmt.Println("read ch data=", i, " k=", k) //k=false i=0 } fmt.Println("check runtime exit") } 

4、向已关闭的channel写，panic

package main import ( "fmt" "time" ) func main() { var ch chan int ch = make(chan int) close(ch) ch <- 1 fmt.Println("end") time.Sleep(time.Second * 1000) } 

5、time.Timer Stop后，time.Timer.C将阻塞

package main import ( "fmt" "time" ) func main() { tm := time.NewTimer(time.Second * 3) go check(tm) time.Sleep(time.Second * 1) tm.Stop() fmt.Println("main runtime end") time.Sleep(time.Second * 1000) } func check(tm *time.Timer) { select { case i, k := <-tm.C: //阻塞 fmt.Println("read ch data=", i, " k=", k) } fmt.Println("check runtime exit") } 

6、无缓冲与有缓冲channel的重要区别，无缓冲的channel在写时必须有读携程，否则会阻塞。如下例子，超时后向exit发数据会阻塞，因为只有一个携程，此时没有其他携程对exit进行读。【踩了坑才理解深刻】

package main import ( "fmt" "time" ) func main() { exit := make(chan int) go check(exit) time.Sleep(time.Second * 100) } func check(exit chan int) { tm := time.NewTimer(time.Second * 3) select { case <-exit: fmt.Println("exit") case <-tm.C: fmt.Println("time out") exit <- 1 fmt.Println("exit <- 1 ok") } fmt.Println("check runtime exit") } 

例子2：

package main import ( "fmt" "time" ) func main() { go func() { for { time.Sleep(time.Second * 1) } }() exit := make(chan int, 1) exit <- 1 fmt.Println("end") } 

这里会直接END，如果exit:=make(chan int),会阻塞在exit<-1

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