how to stop a goroutine which may or may not be running?

Question

I have a go func which I want to stop if running its running in default. The below approach get's blocked at quit <- true if go func already returned.

quit := make(chan bool)
go func() {
    for {
        select {
        case <- quit:
            return
        default:
            // Do other stuff and return if complete.
        }
    }
}()

// Do stuff

// Quit goroutine
quit <- true

Answer 1

Close the quit channel instead of sending a value. The loop will exit because receive on a closed channel returns a zero value.

Also, declare the channel as chan struct{} to indicate that the channel values are unimportant to the program:

quit := make(chan struct{})
go func() {
    for {
        select {
        case <- quit:
            return
        default:
            // Do other stuff and return if complete.
        }
    }
}()

// Do stuff

// Quit goroutine
close(quit)

If you need to break out of "other stuff", then pass the quit channel to the "other stuff" and check every now and again with:

select {
case <- quit:
    return
default:
}
... keep going

If you are doing anything more than the first snippet in this answer, then you should consider using the standard context package for cancelation signals.