Golang内存模型解析-2

Channel通信：

1）Channel的发送和接收，满足Happen-before。（废话）

var c = make(chan int,10)
var a string

func f() {
a = "hello, world"
c <- 0
}

func main() {
go f()
<-c
print(a)
}
上述代码中，a的赋值happen-before写入channel，写入channel happen-before读取channel，读取channel happen-before print

把<-c替换成close，同样结果一样。因为 

                The closing of a channel happensbefore a receive that returns a zero value because the channel is closed.

 说的比较抽象，我的理解是close后，会存在一个阻塞的receive，从而读取所有未发送的数据。

 

2）对于无缓存channel，receive happen-before send。即先阻塞，后传值。带缓存的channel的close不会阻塞，所以无法保证happen-before

var c = make(chan int)
var a string

func f() {
a = "hello, world"
<-c
}
func main() {
go f()
c <- 0
print(a)
}
上述代码回正确打印helloworld，因为a的赋值happen-before receive， receive happen-before send。如果有缓存则不保证正确打印

3）对于缓存容量为C的channel，第k次receive happen-before
k+C次send。