Simple JobQueue for goroutines.

jobqueue.go

import "sync"

type JobQueue struct {
    limit   int
    wg      sync.WaitGroup
    mu      sync.Mutex
    running int
    waiting []func()
}

func NewJobQueue(limit int) *JobQueue {
    return &JobQueue{limit: limit, running: 0}
}

func (q *JobQueue) Enqueue(job func()) {
    q.wg.Add(1)
    wrapper := func() {
        defer q.wg.Done()
        defer func() {
            q.mu.Lock()
            q.running -= 1
            q.mu.Unlock()
            q.reschedule()
        }()
        job()
    }
    q.waiting = append(q.waiting, wrapper)
    q.reschedule()
}

func (q *JobQueue) reschedule() {
    if len(q.waiting) > 0 && q.running < q.limit {
        q.mu.Lock()
        defer q.mu.Unlock()

        first := q.waiting[0]
        q.waiting = q.waiting[1:]
        q.running += 1
        go first()
    }
}

func (q *JobQueue) Wait() {
    q.wg.Wait()
}

// func main() {
//     queue := NewJobQueue(2)
//     for i := 0; i < 9; i++ {
//         queue.Enqueue(func() {
//             time.Sleep(time.Second)
//             t := time.Now()
//             fmt.Printf("Job %v\n", t)
//         })
//     }
//     queue.Wait()
// }