通道就绪后，从多个通道中选择所有值

Question

I'm new in golang and I faced with the problem.

I have several channels.

Some payload gets to this channels in different time.

How I can get all values one by one from channels in the time when channel ready to spit it.

For example I wrote this code:

package main

import (
    "fmt"
    "time"
    "math/rand"
)

func main() {
    arr1 := []int8{1,2,3,4,5}
    arr2 := []int8{6,7,8,9,10}

    c1 := make(chan int8)
    c2 := make(chan int8)

    go func() {
        for _, val := range arr1 {
            time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
            c1 <- val
        }
    }()
    go func() {
        for _, val := range arr2 {
            time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
            c2 <- val
        }
    }()

    select {
        case res1 := <- c1:
            fmt.Println(res1)
        case res2 := <- c2:
            fmt.Println(res2)
    }

    fmt.Println("Hello, test")
}

But in this case, I get only first value, from one of the channels.

Please, give me advise how to solve my issue.

Link to go-play https://play.golang.org/p/FOmkP57YCyR

Answer 1

You have to do couple of things.

1) Make sure you close channels once you are done with source. 2) Iterate over channels until it's closed.

Example:

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    arr1 := []int8{1, 2, 3, 4, 5}
    arr2 := []int8{6, 7, 8, 9, 10}

    c1 := make(chan int8)
    c2 := make(chan int8)

    go func() {
        for _, val := range arr1 {
            time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
            c1 <- val
        }
        close(c1)
    }()
    go func() {
        for _, val := range arr2 {
            time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
            c2 <- val
        }
        close(c2)
    }()

    _c1 := true
    _c2 := true
    var res1, res2 int8

    for _c1 == true || _c2 == true {
        select {
        case res1, _c1 = <-c1:
            if _c1 == true {
                fmt.Println(res1)
            }
        case res2, _c2 = <-c2:
            if _c2 == true {
                fmt.Println(res2)
            }
        }
    }

    fmt.Println("Hello, test")
}

On execution, I got following output on screen.

6
1
7
2
3
4
8
5
9
10
Hello, test