Go併發模式/設計模式之複製請求

複製請求
程序正在處理 用戶的HTTP請求， 或者檢索一個數據塊。你可以將請求分發到多個處理程序（無論是 goroutine ，進程， 還是服務器），其中一個將比其他
處理程序返回更快，可以 立即返回結果。
下面例子 在 單個進程中， 使用多個goroutine 作爲處理程序。
goroutine 將隨機休眠一段時間以模擬不同的負載，

func main() {
	doWork := func(done <-chan interface{}, id int, wg *sync.WaitGroup, result chan <- int) {
		started := time.Now()
		defer wg.Done()

		//模擬隨機負載
		simulatedLoadTime := time.Duration(1 + rand.Intn(5))*time.Second

		select{
		case <-done:
		case <-time.After(simulatedLoadTime):
		}

		select{
		case <-done:
		case result <- id:
		}

		took := time.Since(started)
		//顯示處理程序需要多長時間
		if took < simulatedLoadTime{
			took = simulatedLoadTime
		}

		fmt.Printf("%v took %v\n", id, took)
	}

	done := make(chan interface{})
	result := make(chan int)

	var wg sync.WaitGroup
	wg.Add(10)

	for i := 0; i<10; i++{
		go doWork(done, i, &wg, result)
	}

	firstReturned := <- result
	close(done)
	wg.Wait()

	fmt.Printf("Received an answer from #%v\n", firstReturned)

}

//6 took 1.002598933s
//0 took 1.002687636s
//9 took 2s
//2 took 5s
//3 took 1.002655195s
//4 took 3s
//5 took 2s
//1 took 3s
//8 took 4s
//7 took 2s
//Received an answer from #6

所有的處理程序 都應該是儘可能 等價的，有相同的機會處理請求。
建立和維護這樣一套系統 有很大的代價， 但如果你追求的是響應速度， 那是一種非常有價值的架構。這種方式天然提供了容錯 和 可擴展性。