/*
Copyright 2020 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package parallelize

import (
	"context"
	"math"

	"k8s.io/client-go/util/workqueue"
)

var (
	parallelism = 16
)

// GetParallelism returns the currently set parallelism.
func GetParallelism() int {
	return parallelism
}

// SetParallelism sets the parallelism for all scheduler algorithms.
// TODO(#95952): Remove global setter in favor of a struct that holds the configuration.
func SetParallelism(p int) {
	parallelism = p
}

// chunkSizeFor returns a chunk size for the given number of items to use for
// parallel work. The size aims to produce good CPU utilization.
// returns max(1, min(sqrt(n), n/Parallelism))
func chunkSizeFor(n int) int {
	s := int(math.Sqrt(float64(n)))

	if r := n/parallelism + 1; s > r {
		s = r
	} else if s < 1 {
		s = 1
	}
	return s
}

// Until is a wrapper around workqueue.ParallelizeUntil to use in scheduling algorithms.
func Until(ctx context.Context, pieces int, doWorkPiece workqueue.DoWorkPieceFunc) {
	workqueue.ParallelizeUntil(ctx, parallelism, pieces, doWorkPiece, workqueue.WithChunkSize(chunkSizeFor(pieces)))
}