golang代碼 控制並發數

 

    var sem = make(chan int, 100)


    //--------------------------------------------------------------------------------
    func handle(r *Request) {
        sem <- 1
        process(r)              // 可以控制 process 的並發數
        <-sem
    }

    func Serve(queue chan *Request) {
        for {
            req := <-queue
            go handle(req)        // 但不能控制goroutine的數量，會創建大量阻塞的goroutine
        }
    }

    //--------------------------------------------------------------------------------

    func Serve(queue chan *Request) {
        for req := range queue {
            sem <- 1                    // 改進版本
            go func(req *Request) {
                process(req)
                <-sem
            }(req)
        }
    }

    //--------------------------------------------------------------------------------
    func Serve(queue chan *Request) {
        for req := range queue {
            select {
            case sem <- 1:
                go func(req *Request) {
                    process(req)
                    <-sem
                }(req)
            default:                    // 丟棄這個request
            }
        }
    }