How to get a response from the consumer in a producer / consumer scenario?

Question

I've been trying to use channels to build some kind of producer / consumer. I have a requests channel where the many producers push requests, then I have processRequests that handles the requests.

package main

var requests chan string

func processRequests() {
    for {
        request <- requests
        // Process request...
        // And return response - how?
    }
}

func main() {
    requests = make(chan string)

    go processRequests()

    requests <- "doSomething"
    requests <- "doSomethingElse"
    requests <- "etc"

    select {} // Block forever
}

What I'm wondering is what would be the best way to send back a response to the producer (and to the right one, since there's more than one), once the request is fulfilled? Basically how to make this a two way channel?

Any idea how it could be done?

Answer 1

You should really use two channels. Trying to make it work with one channel will be messy.

There's a Google Sites on the Producer/Consumer pattern that may be useful.

For the producer to know what the consumer is responding to, you could use a struct for the response:

type responseMessage struct {
    Request string
    Response string
}

var requests chan string
var responses chan *responseMessage

func processRequests() {
    for {
        request <- requests
        // Process request...
        responses <- &responseMessage{request, "some response string"}
    }
}

func processResponses() {
    someResponseMessage := <- responses
    if someResponseMessage.Request == "doSomething" {
        // do something!
    }
}

func main() {
    requests = make(chan string)
    responses = make(chan *responseMessage)

    go processRequests()
    go processResponses()

    requests <- "doSomething"
    requests <- "doSomethingElse"
    requests <- "etc"

    select {} // Block forever
}