github.com/m3db/m3@v1.5.0/src/dbnode/encoding/multi_reader_iterator_array_pool.go

// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package encoding

import (
	"sort"
	"sync"

	"github.com/m3db/m3/src/x/pool"
)

// TODO(r): there should be an ArrayPool that can take an alloc function
// that given a "capacity" can return a "interface{}" which consists of an array
// with the specifified capacity and does the bucket logic for the type safe
// higher level specific array pool, i.e. IteratorArrayPool.
// This way we can avoid having the bucketing logic for each pool in each concrete
// array pool.

// TODO(r): instrument this to tune pooling
type multiReaderIteratorArrayPool struct {
	sizesAsc          []pool.Bucket
	buckets           []multiReaderIteratorArrayPoolBucket
	maxBucketCapacity int
}

type multiReaderIteratorArrayPoolBucket struct {
	capacity   int
	values     chan []MultiReaderIterator
	valuesPool *sync.Pool
}

// NewMultiReaderIteratorArrayPool creates a new pool
func NewMultiReaderIteratorArrayPool(sizes []pool.Bucket) MultiReaderIteratorArrayPool {
	sizesAsc := make([]pool.Bucket, len(sizes))
	copy(sizesAsc, sizes)
	sort.Sort(pool.BucketByCapacity(sizesAsc))
	var maxBucketCapacity int
	if len(sizesAsc) != 0 {
		maxBucketCapacity = sizesAsc[len(sizesAsc)-1].Capacity
	}
	return &multiReaderIteratorArrayPool{sizesAsc: sizesAsc, maxBucketCapacity: maxBucketCapacity}
}

func (p *multiReaderIteratorArrayPool) alloc(capacity int) []MultiReaderIterator {
	return make([]MultiReaderIterator, 0, capacity)
}

func (p *multiReaderIteratorArrayPool) Init() {
	buckets := make([]multiReaderIteratorArrayPoolBucket, len(p.sizesAsc))
	for i := range p.sizesAsc {
		buckets[i].capacity = p.sizesAsc[i].Capacity

		if !p.sizesAsc[i].Count.IsDynamic() {
			buckets[i].values = make(chan []MultiReaderIterator, p.sizesAsc[i].Count)
			for j := 0; pool.Size(j) < p.sizesAsc[i].Count; j++ {
				buckets[i].values <- p.alloc(p.sizesAsc[i].Capacity)
			}
			continue
		}

		i := i
		buckets[i].valuesPool = &sync.Pool{New: func() interface{} {
			// NB: if leaking slices is ever a problem, change APIs to return *[]MultiReaderIterator
			return p.alloc(p.sizesAsc[i].Capacity)
		}}
	}
	p.buckets = buckets
}

func (p *multiReaderIteratorArrayPool) Get(capacity int) []MultiReaderIterator {
	if capacity > p.maxBucketCapacity {
		return p.alloc(capacity)
	}
	for i := range p.buckets {
		if p.buckets[i].capacity >= capacity {
			if p.sizesAsc[i].Count.IsDynamic() {
				return p.buckets[i].valuesPool.Get().([]MultiReaderIterator)
			}
			select {
			case b := <-p.buckets[i].values:
				return b
			default:
				// NB(r): use the bucket's capacity so can potentially
				// be returned to pool when it's finished with.
				return p.alloc(p.buckets[i].capacity)
			}
		}
	}
	return p.alloc(capacity)
}

func (p *multiReaderIteratorArrayPool) Put(array []MultiReaderIterator) {
	capacity := cap(array)
	if capacity > p.maxBucketCapacity {
		return
	}

	for i := range array {
		array[i] = nil
	}
	array = array[:0]
	for i := range p.buckets {
		if p.buckets[i].capacity >= capacity {
			if p.sizesAsc[i].Count.IsDynamic() {
				p.buckets[i].valuesPool.Put(array) //nolint:staticcheck
				return
			}
			select {
			case p.buckets[i].values <- array:
			default:
			}
			return
		}
	}
}