Go: one channel with multiple listeners

Question

I am new to go so sorry if the topic is incorrect, but I hope you understand my question. I want to handle events for different running procedures through a channel. Here is a sample code

type Event struct {
    Host string
    Command string
    Output string
}


var (
    incoming        = make(chan Event)
)

func processEmail(ticker* time.Ticker) {
    for {
        select {
        case t := <-ticker.C:
            fmt.Println("Email Tick at", t)
        case e := <-incoming:
            fmt.Println("EMAIL GOT AN EVENT!")
            fmt.Println(e)
        }
    }
}

func processPagerDuty(ticker* time.Ticker) {
    for {
        select {
        case t := <-ticker.C:
            fmt.Println("Pagerduty Tick at", t)
        case e := <-incoming:
            fmt.Println("PAGERDUTY GOT AN EVENT!")
            fmt.Println(e)
        }
    }
}

func main() {

    err := gcfg.ReadFileInto(&cfg, "dispatch-api.cfg")
    if err != nil {
        fmt.Printf("Error loading the config")
    }

    ticker := time.NewTicker(time.Second * 10)
    go processEmail(ticker)

    ticker := time.NewTicker(time.Second * 1)
    go processPagerDuty(ticker)
}


func eventAdd(r render.Render, params martini.Params, req *http.Request) {

    // create an event now
    e := Event{Host: "web01-east.domain.com", Command: "foo", Output: "bar"}
    incoming <- e
}

So, ticker events only work to create. When I call the API call to create an event, I just get the output from the processEmail function. Its all that is called routine, called first, will receive the event on the channel.

Is there a way for both functions to get this event?

Answer 1

You can use a fan and a fan (from Rob Pike's speech):

package main

func main() {
    // feeders - feeder1, feeder2 and feeder3 are used to fan in
    // data into one channel
    go func() {
        for {
            select {
            case v1 := <-feeder1:
                mainChannel <- v1
            case v2 := <-feeder2:
                mainChannel <- v2
            case v3 := <-feeder3:
                mainChannel <- v3
            }
        }
    }()

    // dispatchers - not actually fan out rather dispatching data
    go func() {
        for {
            v := <-mainChannel

            // use this to prevent leaking goroutines
            // (i.e. when one consumer got stuck)
            done := make(chan bool)

            go func() {
                consumer1 <- v
                done <- true
            }()
            go func() {
                consumer2 <- v
                done <- true
            }()
            go func() {
                consumer3 <- v
                done <- true
            }()

            <-done
            <-done
            <-done
        }
    }()

    // or fan out (when processing the data by just one consumer is enough)
    go func() {
        for {
            v := <-mainChannel
            select {
            case consumer1 <- v:
            case consumer2 <- v:
            case consumer3 <- v:
            }
        }
    }()

    // consumers(your logic)
    go func() { <-consumer1 /* using the value */ }()
    go func() { <-consumer2 /* using the value */ }()
    go func() { <-consumer3 /* using the value */ }()
}

type payload int

var (
    feeder1 = make(chan payload)
    feeder2 = make(chan payload)
    feeder3 = make(chan payload)

    mainChannel = make(chan payload)

    consumer1 = make(chan payload)
    consumer2 = make(chan payload)
    consumer3 = make(chan payload)
)

Answer 2

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