golang 基础（25）channel

golang_real.jpg

func chanDemo(){
    // var c chan int
    //定义 c 类型是 chan int 此时为 nil
    c := make(chan int)
    c <- 1
    c <- 2
    n := <-c
    fmt.Println(n)
}

atal error: all goroutines are asleep - deadlock!

运行上面的代码为什么会是 deadlock，这是因为 channel 是 goroutine 和 goroutine 之间通道，这个通道进行发送，如果没有其他通道进行接收就会发生 deadlock。

func chanDemo(){
    // var c chan int
    //定义 c 类型是 chan int 此时为 nil
    c := make(chan int)
    go func(){
        for{
            n := <-c
            fmt.Println(n)
        }
    }()
    c <- 1
    c <- 2
    
}

func main()  {
    chanDemo()
}

这样我们通过匿名函数创建 goroutine 来接受 channel 发送数据，就不会造成 deadlock。在 go 语言中 channel 和 function 一样都是一等公民，我们这里 channel 作为参数和返回值来使用。

go func(){
        for{
            n := <-c
            fmt.Println(n)
        }
    }()

这里 func() 是一个匿名函数作为闭包使用，闭包是可以访问到其环境变量 c 的。我们可让 c 作为参数传入。

func worker(c chan int){
    for{
        n := <-c
        fmt.Println(n)
    }
}

func chanDemo(){
    // var c chan int
    //定义 c 类型是 chan int 此时为 nil
    c := make(chan int)
    go worker(c)
    c <- 1
    c <- 2
    
}

进行改造，将匿名函数提出为 worker 然后将 c 作为参数传入 worker 进行使用。在 worker 中我们接受 channel 发送数据。

func worker(id int,c chan int){
    for{
        fmt.Printf("Worker %d received %c\n",id,<-c)
    }
}

func chanDemo(){
    // var c chan int
    //定义 c 类型是 chan int 此时为 nil
    var channels [10]chan int
    for i:= 0; i < 10; i++{
        channels[i] = make(chan int)
        go worker(i,channels[i])
    }
    
    for i := 0; i < 10; i++{
        channels[i] <- 'a' + i
    }

  
    time.Sleep(time.Millisecond)
    
}

我们可创建 chan 的集合，然后遍历出 10 chan 可以作为参数传入到 worker 中使用，这次我们一次就创建了 10 chan 来用于接受数据，然后再为 worker 添加一个参数作为 channel 的 id 来表示 channel。

Worker 0 received a
Worker 2 received c
Worker 3 received d
Worker 5 received f
Worker 6 received g
Worker 7 received h
Worker 8 received i
Worker 4 received e

for i := 0; i < 10; i++{
        channels[i] <- 'a' + i
    }

    for i := 0; i < 10; i++{
        channels[i] <- 'A' + i
    }

我们可以做个遍历来想channel 传入数据，用于接受。

th.jpeg

Worker 9 received j
Worker 5 received f
Worker 6 received g
Worker 0 received a
Worker 0 received A
Worker 1 received b
Worker 1 received B
Worker 7 received h
Worker 2 received c
Worker 2 received C
Worker 8 received i
Worker 3 received d
Worker 6 received G
Worker 3 received D
Worker 5 received F
Worker 9 received J
Worker 8 received I
Worker 4 received E
Worker 7 received H

这里顺序是乱的，在 workder 虽然接受是按顺序的，但是随后的 fmt.Printf 是 IO 操作。goroutine 会进行调度，调度之后有可能会发送顺序乱。

我们的 channel 还可以作为返回值来使用，现在创建一个 createWorker 这个函数可以返回一个 chan

func createWorker(id int ) chan int{
    c := make(chan int)
    go func(){
        for{
            fmt.Printf("Worker %d received %c\n",id,<-c)
        }
    }()

    return c
}

var channels [10]chan int
for i:= 0; i < 10; i++{
    channels[i] = createWorker(i)
}

th (2).jpeg