Demo how to cancel asynchronous processing after getting exactly n successful results

cancellation-on-success.go

package main

import (
	"fmt"
	"time"

	"github.com/odeke-em/semalim"
)

type echo struct {
	id uint64
}

func (e echo) Do() (interface{}, error) { return fmt.Sprintf("done %d", e.id), nil }
func (e echo) Id() interface{}          { return e.id }

var _ semalim.Job = (*echo)(nil)

func main() {
	jobsChan := make(chan semalim.Job)
	cancellation := make(chan bool)
	go func() {
		defer close(jobsChan)

		throttle := time.NewTicker(1e9 / 20)
		id := uint64(0)
		working := true
		for working {
			select {
			case <-cancellation: // If they cancel on us, stop all work and break
				working = false
				break
			case <-throttle.C:
				jobsChan <- &echo{id: id}
				id += 1
			}
		}
	}()

	defer close(cancellation)
	resultsChan := semalim.Run(jobsChan, 10)

	success := uint64(0)
	for res := range resultsChan {
		if success >= 10000 {
			// We've reached out limit, time to break out
			// but also send the cancellation signal
			fmt.Printf("\033[32mcancellation now\033[00m\n")
			cancellation <- true
			break
		}

		// We are only counting successes
		if err := res.Err(); err == nil {
			success += 1
		}
	}
}