Wait for one goroutine to finish

Question

I am running a cpu intensive script on 8 different goroutines. Each of these goroutines will take at least a few minutes to complete, and I was wondering if something like this is possible:

for i := 0; i < len(input); i += 1 {
  wait_for_number_of_processes_running_to_be_less_than_8
  go calc_math_and_things(input[i])
}

Answer 1

You could use a buffered channel to return result of a goroutine and indicate termination, and when you read from this channel you start a new go routine. Something like that:

const maxNRoutine = 8
var routineCtr int
var resultCh = make(chan int, maxNRoutine)

for i := 0; i < len(input); i += 1 {
    if routineCtr < maxNRoutines {
        go calc_math_and_things(resultCh, input[i])
        routineCtr++
        continue
    }
    var result = <- resultCh // go routine is done, log result and start a new one
    println(result)
    go calc_math_and_things(resultCh, intput[i])
}

Inside your routine:

func calc_math_and_things(resultCh chan<- int, input byte) {
     // ... do some stuff
     resultCh <- 1
}