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
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)
}
func main() {
in := make(chan bool)
close(in)
go func() { <-in }()
in <- true // panic: send on closed channel
}
func main() {
in := make(chan int, 2)
close(in)
_, ok := <-in
log.Printf("ok:%v", ok) // ok:false
}