vitess.io/vitess@v0.16.2/go/bucketpool/bucketpool.go (about)

     1  /*
     2  Copyright 2019 The Vitess Authors
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package bucketpool
    18  
    19  import (
    20  	"math/bits"
    21  	"sync"
    22  )
    23  
    24  type sizedPool struct {
    25  	size int
    26  	pool sync.Pool
    27  }
    28  
    29  func newSizedPool(size int) *sizedPool {
    30  	return &sizedPool{
    31  		size: size,
    32  		pool: sync.Pool{
    33  			New: func() any { return makeSlicePointer(size) },
    34  		},
    35  	}
    36  }
    37  
    38  // Pool is actually multiple pools which store buffers of specific size.
    39  // i.e. it can be three pools which return buffers 32K, 64K and 128K.
    40  type Pool struct {
    41  	minSize int
    42  	maxSize int
    43  	pools   []*sizedPool
    44  }
    45  
    46  // New returns Pool which has buckets from minSize to maxSize.
    47  // Buckets increase with the power of two, i.e with multiplier 2: [2b, 4b, 16b, ... , 1024b]
    48  // Last pool will always be capped to maxSize.
    49  func New(minSize, maxSize int) *Pool {
    50  	if maxSize < minSize {
    51  		panic("maxSize can't be less than minSize")
    52  	}
    53  	const multiplier = 2
    54  	var pools []*sizedPool
    55  	curSize := minSize
    56  	for curSize < maxSize {
    57  		pools = append(pools, newSizedPool(curSize))
    58  		curSize *= multiplier
    59  	}
    60  	pools = append(pools, newSizedPool(maxSize))
    61  	return &Pool{
    62  		minSize: minSize,
    63  		maxSize: maxSize,
    64  		pools:   pools,
    65  	}
    66  }
    67  
    68  func (p *Pool) findPool(size int) *sizedPool {
    69  	if size > p.maxSize {
    70  		return nil
    71  	}
    72  	div, rem := bits.Div64(0, uint64(size), uint64(p.minSize))
    73  	idx := bits.Len64(div)
    74  	if rem == 0 && div != 0 && (div&(div-1)) == 0 {
    75  		idx = idx - 1
    76  	}
    77  	return p.pools[idx]
    78  }
    79  
    80  // Get returns pointer to []byte which has len size.
    81  // If there is no bucket with buffers >= size, slice will be allocated.
    82  func (p *Pool) Get(size int) *[]byte {
    83  	sp := p.findPool(size)
    84  	if sp == nil {
    85  		return makeSlicePointer(size)
    86  	}
    87  	buf := sp.pool.Get().(*[]byte)
    88  	*buf = (*buf)[:size]
    89  	return buf
    90  }
    91  
    92  // Put returns pointer to slice to some bucket. Discards slice for which there is no bucket
    93  func (p *Pool) Put(b *[]byte) {
    94  	sp := p.findPool(cap(*b))
    95  	if sp == nil {
    96  		return
    97  	}
    98  	*b = (*b)[:cap(*b)]
    99  	sp.pool.Put(b)
   100  }
   101  
   102  func makeSlicePointer(size int) *[]byte {
   103  	data := make([]byte, size)
   104  	return &data
   105  }