[GO channel deadlock]在处理通道数据时遇到死锁问题无法对应到通道是在哪个场景下被阻塞。 代码不难，只为搞懂阻塞。

一个channel不能解决的问题那就用两个~~

package main

import (
    "fmt"
    "time"
)

func test(num int, ch chan int, counter chan struct{}) {
    for i := (num - 1) * 30; i < num*30; i++ {
        if i%2 == 0 {
            ch <- i
        }
    }
    counter <- struct{}{}
}

func main() {

    var count int
    var ch chan int = make(chan int, 1)
    var counter chan struct{} = make(chan struct{}, 4)

    timerc := time.NewTimer(2 * time.Second)

    for i := 1; i <= 4; i++ {
        go test(i, ch, counter)
    }

OUTFOR:
    for {
        timerc.Reset(2 * time.Second)
        select {
        case tmp := <-ch:

            fmt.Println(tmp)
        case <-counter:

            count++
        case <-timerc.C:

            if count == 4 {
                break OUTFOR
            }
        }
    }

    close(ch)
    close(counter)
}

简化下楼主代码：

package main

import (
    "fmt"
    "sync"
)

var locker sync.Mutex

func test(ch chan int) {
    fmt.Println("test start")
    for i := 0; i < 10; i++ {
        if i%2 == 0 {
            locker.Lock()
            ch <- i
            locker.Unlock()
        }
    }
    fmt.Println("test end")
}

func main() {

    var ch chan int = make(chan int)
    go test(ch)
    defer close(ch)

    for v := range ch {
        fmt.Println(v)
    }
}

执行：

❯ go run demo1.go
test start
0
2
4
6
test end
8
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
        /tmp/demo1.go:28 +0xff
exit status 2

重点关注这句 fatal error: all goroutines are asleep - deadlock!

test函数所在goroutines 已经执行完退出，只剩下main goroutines ，而这个唯一的goroutines 又阻塞了，这不就死锁了。

代码再简化下直接把test部分删去，也是一样的效果。

func main() {
    var ch = make(chan int, 5)
    defer close(ch)

    go test(ch)

    select {
    case v := <-ch:
        fmt.Println(v)
    }
}