Always have x number of goroutines running at any time

Question

I see lots of tutorials and examples on how to make Go wait for x number of goroutines to finish, but what I\'m trying to do is have ensure there are always x number running

Answer 1

This is a simple producer-consumer problem, which in Go can be easily solved using channels to buffer the paquets.

To put it simple: create a channel that accept your IDs. Run a number of routines which will read from the channel in a loop then process the ID. Then run your loop that will feed IDs to the channel.

Example:

func producer() {
    var buffer = make(chan uint)

    for i := 0; i < 20; i++ {
        go consumer(buffer)
    }

    for _, id :=  range IDs {
        buffer <- id
    }
}

func consumer(buffer chan uint) {
    for {
        id := <- buffer
        // Do your things here
    }
}

Things to know:

• Unbuffered channels are blocking: if the item wrote into the channel isn't accepted, the routine feeding the item will block until it is
• My example lack a closing mechanism: you must find a way to make the producer to wait for all consumers to end their loop before returning. The simplest way to do this is with another channel. I let you think about it.