CODEWITHSUNDEEP
concurrencygo
user310291
user310291

Reputation: 38180

Go Select and multiple cases at once

How to adapt the code below to do something when C1 and C2 have been BOTH received https://gobyexample.com/select

import "time"
import "fmt"

func main() {

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

    go func() {
        time.Sleep(time.Second * 1)
        c1 <- "one"
    }()
    go func() {
        time.Sleep(time.Second * 2)
        c2 <- "two"
    }()

    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}

Upvotes: 7

Views: 11863

Answers (1)

VonC
VonC

Reputation: 1323433

That could be a pipeline technique, called fan-in:

A function can read from multiple inputs and proceed until all are closed by multiplexing the input channels onto a single channel that's closed when all the inputs are closed. This is called fan-in. 

func merge(cs ...<-chan int) <-chan int {
    var wg sync.WaitGroup
    out := make(chan string)

    // Start an output goroutine for each input channel in cs.  output
    // copies values from c to out until c is closed or it receives a value
    // from done, then output calls wg.Done.
    output := func(c <-chan string) {
        for n := range c {
            select {
            case out <- "received " + n:
            case <-done:
            }
        }
        wg.Done()
    }
    wg.Add(len(cs))
    for _, c := range cs {
        go output(c)
    }

    // Start a goroutine to close out once all the output goroutines are
    // done.  This must start after the wg.Add call.
    go func() {
        wg.Wait()
        close(out)
    }()
    return out
}

See a complete example in this playground

Note: whatever solution you will end up using, a good read remains:

Principles of designing Go APIs with channels by Alan Shreve.

In particular:

Principle #1

An API should declare the directionality of its channels.

Upvotes: 7

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