package main

import (
    "fmt"
    "time"
)

func generator() chan int{
    out := make(chan int)
    go func() {
        i:=0
        for true {
            time.Sleep(time.Second)
            out <- i
            i++
        }
    }()

    return out
}

func worker(id int, w chan int) {
    for n := range w {
        time.Sleep(time.Second * 5)
        fmt.Printf("Worker %d received %d\n", id, n)
    }
}

func createWorker(id int) chan<- int {
    w := make(chan int)
    go worker(id, w)
    return w
}

func main() {
    var c1, c2 = generator(), generator()

    worker := createWorker(0)

    // channel 是同步阻塞的，如果不想阻塞就可以使用select
    n := 0
    hasVaule := false
    for  {
        var activeWorker chan<- int  // activeWorker 默认是nil，所以不会case到
        if hasVaule {
            activeWorker = worker // worker 给activeWorker，会case到
        }
        select {
        case n = <-c1:
            hasVaule = true
        case n = <-c2:
            hasVaule = true
        case activeWorker<-n: // 注意如果这里消耗太慢，前面的n可能被覆盖多次了
            hasVaule = false
        }
    }

}

为了避免任务处理太慢，n被覆盖，所以我们把所有值放到values

package main

import (
    "fmt"
    "time"
)

func generator() chan int{
    out := make(chan int)
    go func() {
        i:=0
        for true {
            time.Sleep(time.Second)
            out <- i
            i++
        }
    }()

    return out
}

func worker(id int, w chan int) {
    for n := range w {
        time.Sleep(time.Second * 5)
        fmt.Printf("Worker %d received %d\n", id, n)
    }
}

func createWorker(id int) chan<- int {
    w := make(chan int)
    go worker(id, w)
    return w
}

func main() {
    var c1, c2 = generator(), generator()

    worker := createWorker(0)

    var values []int
    for  {
        var activeWorker chan<- int
        var activeValue int

        // 只要values有内容，就把值送到worker
        if len(values) > 0{
            activeWorker = worker
            activeValue = values[0]
        }
        select {
        case n := <-c1:
            values = append(values, n)     // 把所有的值都放到values
        case n := <-c2:
            values = append(values, n)     // 把所有的值都放到values
        case activeWorker<-activeValue: // 每次从values拿一个值发送过去
            values = values[1:]
        }
    }

}