done := make(chan bool)
				go func() {
					f()
					done <- true
				}()
				return done
			}
			started := false
			switch call.typ {
			case add1:
				signal := doCall(ctx.waitParallel)
				select {
				case <-signal:
					started = true
				case ctx.startParallel <- true:
					<-signal
				}
			case done:
				signal := doCall(ctx.release)
				select {
				case <-signal: