Function ParHeapOr

parallel.go:184–259

ParHeapOr computes the union (OR) of all provided bitmaps in parallel, where the parameter "parallelism" determines how many workers are to be used (if it is set to 0, a default number of workers is chosen) ParHeapOr uses a heap to compute the union. For rare cases it might be faster than ParOr

(parallelism int, bitmaps ...*Bitmap)

// (if it is set to 0, a default number of workers is chosen)
// ParHeapOr uses a heap to compute the union. For rare cases it might be faster than ParOr
func ParHeapOr(parallelism int, bitmaps ...*Bitmap) *Bitmap {

	bitmapCount := len(bitmaps)
	if bitmapCount == 0 {
		return NewBitmap()
	} else if bitmapCount == 1 {
		return bitmaps[0].Clone()
	}

	if parallelism == 0 {
		parallelism = defaultWorkerCount
	}

	h := newBitmapContainerHeap(bitmaps...)

	bitmapChan := make(chan *Bitmap)
	inputChan := make(chan multipleContainers, 128)
	resultChan := make(chan keyedContainer, 32)
	expectedKeysChan := make(chan int)

	pool := sync.Pool{
		New: func() interface{} {
			return make([]container, 0, len(bitmaps))
		},
	}

	orFunc := func() {
		// Assumes only structs with >=2 containers are passed
		for input := range inputChan {
			c := toBitmapContainer(input.containers[0]).lazyOR(input.containers[1])
			for _, next := range input.containers[2:] {
				c = c.lazyIOR(next)
			}
			c = repairAfterLazy(c)
			kx := keyedContainer{
				input.key,
				c,
				input.idx,
			}
			resultChan <- kx
			pool.Put(input.containers[:0])
		}
	}

	go appenderRoutine(bitmapChan, resultChan, expectedKeysChan)

	for i := 0; i < parallelism; i++ {
		go orFunc()
	}

	idx := 0
	for h.Len() > 0 {
		ck := h.Next(pool.Get().([]container))
		if len(ck.containers) == 1 {
			resultChan <- keyedContainer{
				ck.key,
				ck.containers[0],
				idx,