golang中管道热替换

golang中管道替换问题

https://blog.csdn.net/cyk2396/article/details/78875347

1.运行以下代码：

var chan1 chan int
var chanLength int = 18
var interval time.Duration = 1500 * time.Millisecond

//var interval2 time.Duration = 1800 * time.Millisecond

//golang在替换通道时引起的问题
func main() {
chan1 = make(chan int, chanLength)
//该goroutine是每隔1.5秒向chan1中发送一个元素，
//当满足条件时，重置chan1,此时chan1会指向一个新通道
go func() {
for i := 0; i < chanLength; i++ {
if i > 0 && i%3 == 0 {
fmt.Println("chan1 reset")
chan1 = make(chan int, chanLength)
}
fmt.Println("send an value : ", i)
chan1 <- i
time.Sleep(interval)
}
fmt.Println("close chan1")
close(chan1)
}()

//用于接收chan1中的元素
receive(chan1)

}

func receive(chan2 chan int) {
fmt.Println("start receive value from chan1 ...")
timer := time.After(30 * time.Second)
Loop:
for {
select {
case e, ok := <-chan2:
if !ok {
fmt.Println("chan1 has closed ...")
break Loop
}

		fmt.Println("receive value : ", e)
		time.Sleep(interval)
	case <-timer:
		fmt.Println("time out")
		break Loop
	}
}

}
结果如下：

start receive value from chan1 ...
send an value : 0
receive value : 0
send an value : 1
receive value : 1
send an value : 2
receive value : 2
chan1 reset
send an value : 3
send an value : 4
send an value : 5
chan1 reset
send an value : 6
send an value : 7
send an value : 8
chan1 reset
send an value : 9
send an value : 10
send an value : 11
chan1 reset
send an value : 12
send an value : 13
send an value : 14
chan1 reset
send an value : 15
send an value : 16
send an value : 17
close chan1
time out
引起这个的原因是：对变量的重新赋值操作是无法被传递的。在上面这个demo中，当chan1指向了新管道时，receive()函数还是调用原来的旧管道。

解决办法是:通过函数调用每次都获取最新的管道。代码如下：

var chan1 chan int
var chanLength int = 18
var interval time.Duration = 1500 * time.Millisecond

var interval2 time.Duration = 1550 * time.Millisecond

//golang在替换通道时引起的问题
func main() {
chan1 = make(chan int, chanLength)
//该goroutine是每隔1.5秒向chan1中发送一个元素，
//当满足条件时，重置chan1,此时chan1会指向一个新通道
go func() {
for i := 0; i < chanLength; i++ {
if i > 0 && i%3 == 0 {
fmt.Println("chan1 reset")
chan1 = make(chan int, chanLength)
}
fmt.Println("send an value : ", i)
chan1 <- i
time.Sleep(interval)
}
fmt.Println("close chan1")
close(chan1)
}()

//用于接收chan1中的元素
receive()

}

func receive() {
fmt.Println("start receive value from chan1 ...")
timer := time.After(30 * time.Second)
Loop:
for {
select {
case e, ok := <-getChan(): //通过getChan()每次都获取最新的管道
if !ok {
fmt.Println("chan1 has closed ...")
break Loop
}

		fmt.Println("receive value : ", e)
		time.Sleep(interval2) // 时间间隔相比发送方的时间间隔增加50ms，为了在getChan()时能获取最新的chan
	case <-timer:
		fmt.Println("time out")
		break Loop
	}
}

}

//获取管道chan1
func getChan() chan int {
return chan1
}