channel

README

golang channel tips

1.向关闭的channel发送数据会panic

2.重复关闭channel会导致panic

3.从关闭的channel读数据不会panic,读出channel中已有的数据之后再读就是channel类似的默认值,比如chan int类型的channel关闭之后读取到的值为0

4.当channel是nil的时候,无论是传入数据还是取出数据,都会永久的block

5.所有的goroutines协程都处于休眠(阻塞)状态时会报错:"all goroutines are asleep - deadlock!"

操作	nil channel	closed channel	not-closed non-nil channel
close	panic	panic	成功 close
写 ch <-	一直阻塞	panic	阻塞或成功写入数据
读 <- ch	一直阻塞	读取对应类型零值	阻塞或成功读取数据

写入 关闭的channel

向关闭的channel中写入数据时会触发painc操作

panic 类型: runtime.plainError

panic 值: "send on closed channel"

读取 关闭的channel

往关闭的channel中读数据时, 当读到第二个返回值为false时 就表示已无数据;

v, ok := <- chan

0-1-channel-close

go build -gcflags "-N -l" -ldflags=-compressdwarf=false -o 0-1-channel-close.out 0-1-channel-close.go
go tool objdump -s "main.main" 0-1-channel-close.out > 0-1-channel-close.S

汇编分析

func main() {
	in := make(chan int, 2) // CALL runtime.makechan(SB)
	in <- 1                 // CALL runtime.chansend1(SB)
	close(in)               // CALL runtime.closechan(SB)
	_, ok := <-in           // CALL runtime.chanrecv2(SB)

	// LEAQ runtime.staticbytes(SB), DX
	// LEAQ go.string.*+794(SB), AX
	// CALL log.Printf(SB)
	log.Printf("ok:%v", ok)
	// LEAQ runtime/internal/sys.DefaultGoroot.str+376(SB), CX
	// LEAQ runtime.staticbytes(SB), CX
	// CALL fmt.Println(SB)
	fmt.Println("ok:", ok)
}

0-2-send-on-closed-channel

func main() {
	in := make(chan bool)
	close(in)
	go func() { <-in }()
	in <- true // panic: send on closed channel
}

0-3-read-on-closed-channel

func main() {
	in := make(chan int, 2)
	close(in)
	_, ok := <-in
	log.Printf("ok:%v", ok) // ok:false
}