go語言channel的別樣用法

1.返回值使用通道

func main() {
    // 生成隨機數做爲一個服務
    randService := randGenerator()
    // 從服務中讀取隨機數並打印
    fmt.Printf("%d\n",<-randService)
}
func randGenerator() chan int {
    // 建立通道
    out := make(chan int)
    // 建立協程
    go func() {
        for {
            //向通道內寫入數據，若是無人讀取會等待
            out <- rand.Int()
        }
    }()
    return out
}

2.參數使用通道

//一個查詢結構體
type query struct {
    //參數Channel
    sql chan string
    //結果Channel
    result chan string
}
//執行Query
func execQuery(q query) {
    //啓動協程
    go func() {
        //獲取輸入
        sql := <-q.sql
        //訪問數據庫，輸出結果通道
        q.result <- "get" + sql
    }()
}
func main() {
    //初始化Query
    q := query{make(chan string, 1),make(chan string, 1)}
    //執行Query，注意執行的時候無需準備參數
    execQuery(q)
    //準備參數
    q.sql <- "select * from table"
    //獲取結果
    fmt.Println(<-q.result)
}

3.併發循環

func doSomething(num int) (sum int) {
    for i := 1; i <= 10; i++ {
        fmt.Printf("%d + %d = %d\n", num, num + i, num + num + i)
        sum = sum + num + i
    }
    return sum
}
func testLoop() {
    // 創建計數器，通道大小爲cpu核數
    var NumCPU = runtime.NumCPU()
    fmt.Printf("NumCPU = %d\n", NumCPU)
    sem :=make(chan int, NumCPU);
    //FOR循環體
    data := []int{1, 11, 21, 31, 41, 51, 61, 71, 81, 91}
    for _,v:= range data {
        //創建協程
        go func (v int) {
            fmt.Printf("doSomething(%d)...\n", v)
            sum := doSomething(v);
            //計數
            sem <- sum;
        } (v);
    }
    // 等待循環結束
    var total int = 0
    for i := 0; i < len(data); i++ {
        temp := <- sem
        fmt.Printf("%d <- sem\n", temp)
        total = total + temp
    }
    fmt.Printf("total = %d\n", total)
}
func main() {
    testLoop()
}

4.利用channel計算素數

// Send the sequence 2, 3, 4, ... to channel 'in'.
func Generate(ch chan int) {
    for i := 2; ; i++ {
        ch<- i // Send 'i' to channel 'in'.
    }
}
// Copy the values from channel 'in' to channel 'out',
// removing those divisible by 'prime'.
func Filter(in chan int, out chan int, prime int) {
    for {
        i := <-in // Receive valuefrom 'in'.
        if i%prime != 0 {
            out <- i // Send'i' to 'out'.
        }
    }
}
func main() {
    in := make(chan int)
    go Generate(in)      // Launch Generate goroutine.
    for i := 0; i < 100; i++ {
        prime := <-in
        print(prime, "\n")
        out := make(chan int)
        go Filter(in, out, prime)
        in = out
    }
}

5.共享變量的讀寫

//共享變量有一個讀通道和一個寫通道組成
type shardedVar struct {
    reader chan int
    writer chan int
}
//共享變量維護協程
func whachdog(v shardedVar) {
    go func() {
        //初始值
        var value int = 0
        for {
            //監聽讀寫通道，完成服務
            select {
            case value = <-v.writer:
            case v.reader <-value:
            }
        }
    }()
}
func main() {
    //初始化，並開始維護協程
    v := shardedVar{make(chan int), make(chan int)}
    whachdog(v)
    //讀取初始值
    fmt.Println(<-v.reader)
    //寫入一個值
    v.writer <- 1
    //讀取新寫入的值
    fmt.Println(<-v.reader)
}

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http://www.codeforfun.info/