並發控制 Cancel Example

通過使用WithCancel可以取消一個或多個goroutine的執行，以實現對並發的控制。

package main 

import (
    "context"
    "fmt"
    "time"
)

func PrintTask(ctx context.Context) {

    for {
    
        select {
        
        case <- ctx.Done():
            return
        default:
            time.Sleep(2*time.Second)
            fmt.Println("A man must walk down many roads.")
        }
    
    }


}


func main() {

    ctx := context.Background()
    ctx, cancel := context.WithCancel(ctx)
    
    defer cancel()

    go PrintTask(ctx)
    go PrintTask(ctx)
    go PrintTask(ctx)

    time.Sleep(3*time.Second)
    fmt.Println("main exit...")
}

 

WithCancel返回cancel函數，調用cancel函數會關閉Done channel，PrintTask就會結束。

output

A man must walk down many roads.

A man must walk down many roads.

A man must walk down many roads.

main exit...

並發超時控制 Timeout Example

WithTimeout可以實現並發超時控制，使goroutine執行超時時自動結束。

package main 

import (
    "context"
    "fmt"
    "time"
)


func main() {

    ctx := context.Background()
    timeout := 50*time.Millisecond
    ctx, cancel := context.WithTimeout(ctx, timeout)
    
    defer cancel()

    done := make(chan int,1)

    go func() {
        // do something
        time.Sleep(1*time.Second)
        done<- 1
    }()

    select{
    case <-done:
        fmt.Println("work done on time")
    case <-ctx.Done():
        // timeout
        fmt.Println(ctx.Err())
    }


    fmt.Println("main exit...")
}


 

output:

context deadline exceeded

main exit...

Go並發控制--context的使用