group.go

package pond

import (
	"context"
	"sync"
)

// TaskGroup represents a group of related tasks
type TaskGroup struct {
	pool      *WorkerPool
	waitGroup sync.WaitGroup
}

// Submit adds a task to this group and sends it to the worker pool to be executed
func (g *TaskGroup) Submit(task func()) {
	g.waitGroup.Add(1)

	g.pool.Submit(func() {
		defer g.waitGroup.Done()

		task()
	})
}

// Wait waits until all the tasks in this group have completed
func (g *TaskGroup) Wait() {

	// Wait for all tasks to complete
	g.waitGroup.Wait()
}

// TaskGroupWithContext represents a group of related tasks associated to a context
type TaskGroupWithContext struct {
	TaskGroup
	ctx     context.Context
	cancel  context.CancelFunc
	errOnce sync.Once
	err     error
}

// Submit adds a task to this group and sends it to the worker pool to be executed
func (g *TaskGroupWithContext) Submit(task func() error) {
	g.waitGroup.Add(1)

	g.pool.Submit(func() {
		defer g.waitGroup.Done()

		// If context has already been cancelled, skip task execution
		if g.ctx != nil {
			select {
			case <-g.ctx.Done():
				return
			default:
			}
		}

		// don't actually ignore errors
		err := task()
		if err != nil {
			g.errOnce.Do(func() {
				g.err = err
				if g.cancel != nil {
					g.cancel()
				}
			})
		}
	})
}

// Wait blocks until either all the tasks submitted to this group have completed,
// one of them returned a non-nil error or the context associated to this group
// was canceled.
func (g *TaskGroupWithContext) Wait() error {

	// Wait for all tasks to complete
	tasksCompleted := make(chan struct{})
	go func() {
		g.waitGroup.Wait()
		tasksCompleted <- struct{}{}
	}()

	select {
	case <-tasksCompleted:
		// If context was provided, cancel it to signal all running tasks to stop
		g.cancel()
	case <-g.ctx.Done():
	}

	return g.err
}