如何在没有死锁的情况下在缓冲通道上循环？

Question

I'm wondering how can I drain / close the buffered channels so that I don't get into the deadlock? I'm using range to loop through the channels but it seems that although they are "read" they don't get closed like the non-buffered channels do.

package main

func main() {

    cp := 2
    ch := make(chan string, cp)

    for i := 0; i < cp; i++ {
        go send(ch)
    }
    go send(ch)

    for lc := range ch {
        print(lc)

    }

}

func send(ch chan string) {

    ch <- "hello
"

}

Play

Answer 1

You can close channels using the close() builtin. This has to be called after all of your concurrent processing is done. How you're doing that depends on what you want to do.

In your current architecture it seems that you have to establish a global state, something that tracks all your processes and determines that the last one finished. Such a state can be achieved by using a sync.WaitGroup for example.

func send(c chan string, wg *sync.WaitGroup) {
    defer wg.Done()
    // ...
}

wg := &sync.WaitGroup{}

for i := 0; i < cp; i++ {
    wg.Add(1)
    go send(ch, wg)
}
wg.Add(1)
go send(ch, wg)

wg.Wait()
close(ch)

for e := range(ch) {
    // ...
}

Note that closing the channel and then iterating over it will give you only the elements that are queued in the channel. This means that any goroutine that wanted to put a value in the channel can't do this anymore as the channel is closed.