async.go

var sem = make(chan int, MaxOutstanding)

func handle(r *Request) {
    <-sem          // Wait for active queue to drain.
    process(r)     // May take a long time.
    sem <- 1       // Done; enable next request to run.
}

func init() {
    for i := 0; i < MaxOutstanding; i++ {
        sem <- 1
    }
}

func Serve(queue chan *Request) {
    for {
        req := <-queue
        go handle(req)  // Don't wait for handle to finish.
    }
}