How to send message to multiple channels in go

Question

so my question is how to send message to channels that broadcast function gets only if channel is not closed and just for once.

after sending message should increase sentNumber.

I say just to remind, there is a time limit for sending message to all channels!

package main

import (
    "fmt"
    "sync"
    "time"
)

var (
    sentNumber int
)

func broadcast(waitTime time.Duration, message string, ch ...chan string) (sentNumber int) {
    start := time.Now()
    for _, channel := range ch {
        if time.Since(start) >= waitTime {
            break
        }
        go send(channel, message)
    }
    return 0
}

func send(channel chan string, message string) {
    for {
        if _,open := <-channel; open{
            break
        }
    }
    var wg sync.WaitGroup
    wg.Add(1)
    go func() {
        wg.Done()
        channel <- message
    }()
    wg.Wait()
}

func main() {
    a := make(chan string, 1)
    b := make(chan string, 1)
    broadcast(5, "secret message", a, b)
    fmt.Println(<-a)
    fmt.Println(<-b)
}

emptyhua · Accepted Answer · 2021-10-15T02:30:18.257

time.Since(start) >= waitTime can't break the send function
go send(channel, message) should not be more efficient than a single thread queue in this case
broadcast has no responsibility to check if channel has been closed, channels were not created/closed by broadcast

package main

import (
    "context"
    "fmt"
    "time"
)

func broadcast(waitTime time.Duration, message string, chs ...chan string) (sentNumber int) {
    ctx, cancel := context.WithTimeout(context.Background(), waitTime)
    defer cancel()

    jobQueue := make(chan chan string, len(chs))
    for _, c := range chs {
        jobQueue <- c
    }

queue:
    for c := range jobQueue {
        select {
        case c <- message:
            // sent success
            sentNumber += 1
            if sentNumber == len(chs) {
                cancel()
            }
        case <-ctx.Done():
            // timeout, break job queue
            break queue
        default:
            // if send failed, retry later
            jobQueue <- c
        }
    }

    return
}

func main() {
    a := make(chan string)
    b := make(chan string)

    go func() {
        time.Sleep(time.Second)
        fmt.Println("a:", <-a)
    }()

    go func() {
        time.Sleep(3 * time.Second)
        fmt.Println("b:", <-b)
    }()

    c := broadcast(2*time.Second, "secret message", a, b)
    fmt.Printf("sent count:%d\n", c)

    time.Sleep(3 * time.Second)
}

How to send message to multiple channels in go

1 Answers1