/usr/share/gocode/src/github.com/syndtr/goleveldb/leveldb/util/buffer_pool.go is in golang-github-syndtr-goleveldb-dev 0.0~git20170725.0.b89cc31-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 | // Copyright (c) 2014, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package util
import (
"fmt"
"sync"
"sync/atomic"
"time"
)
type buffer struct {
b []byte
miss int
}
// BufferPool is a 'buffer pool'.
type BufferPool struct {
pool [6]chan []byte
size [5]uint32
sizeMiss [5]uint32
sizeHalf [5]uint32
baseline [4]int
baseline0 int
mu sync.RWMutex
closed bool
closeC chan struct{}
get uint32
put uint32
half uint32
less uint32
equal uint32
greater uint32
miss uint32
}
func (p *BufferPool) poolNum(n int) int {
if n <= p.baseline0 && n > p.baseline0/2 {
return 0
}
for i, x := range p.baseline {
if n <= x {
return i + 1
}
}
return len(p.baseline) + 1
}
// Get returns buffer with length of n.
func (p *BufferPool) Get(n int) []byte {
if p == nil {
return make([]byte, n)
}
p.mu.RLock()
defer p.mu.RUnlock()
if p.closed {
return make([]byte, n)
}
atomic.AddUint32(&p.get, 1)
poolNum := p.poolNum(n)
pool := p.pool[poolNum]
if poolNum == 0 {
// Fast path.
select {
case b := <-pool:
switch {
case cap(b) > n:
if cap(b)-n >= n {
atomic.AddUint32(&p.half, 1)
select {
case pool <- b:
default:
}
return make([]byte, n)
} else {
atomic.AddUint32(&p.less, 1)
return b[:n]
}
case cap(b) == n:
atomic.AddUint32(&p.equal, 1)
return b[:n]
default:
atomic.AddUint32(&p.greater, 1)
}
default:
atomic.AddUint32(&p.miss, 1)
}
return make([]byte, n, p.baseline0)
} else {
sizePtr := &p.size[poolNum-1]
select {
case b := <-pool:
switch {
case cap(b) > n:
if cap(b)-n >= n {
atomic.AddUint32(&p.half, 1)
sizeHalfPtr := &p.sizeHalf[poolNum-1]
if atomic.AddUint32(sizeHalfPtr, 1) == 20 {
atomic.StoreUint32(sizePtr, uint32(cap(b)/2))
atomic.StoreUint32(sizeHalfPtr, 0)
} else {
select {
case pool <- b:
default:
}
}
return make([]byte, n)
} else {
atomic.AddUint32(&p.less, 1)
return b[:n]
}
case cap(b) == n:
atomic.AddUint32(&p.equal, 1)
return b[:n]
default:
atomic.AddUint32(&p.greater, 1)
if uint32(cap(b)) >= atomic.LoadUint32(sizePtr) {
select {
case pool <- b:
default:
}
}
}
default:
atomic.AddUint32(&p.miss, 1)
}
if size := atomic.LoadUint32(sizePtr); uint32(n) > size {
if size == 0 {
atomic.CompareAndSwapUint32(sizePtr, 0, uint32(n))
} else {
sizeMissPtr := &p.sizeMiss[poolNum-1]
if atomic.AddUint32(sizeMissPtr, 1) == 20 {
atomic.StoreUint32(sizePtr, uint32(n))
atomic.StoreUint32(sizeMissPtr, 0)
}
}
return make([]byte, n)
} else {
return make([]byte, n, size)
}
}
}
// Put adds given buffer to the pool.
func (p *BufferPool) Put(b []byte) {
if p == nil {
return
}
p.mu.RLock()
defer p.mu.RUnlock()
if p.closed {
return
}
atomic.AddUint32(&p.put, 1)
pool := p.pool[p.poolNum(cap(b))]
select {
case pool <- b:
default:
}
}
func (p *BufferPool) Close() {
if p == nil {
return
}
p.mu.Lock()
if !p.closed {
p.closed = true
p.closeC <- struct{}{}
}
p.mu.Unlock()
}
func (p *BufferPool) String() string {
if p == nil {
return "<nil>"
}
return fmt.Sprintf("BufferPool{B·%d Z·%v Zm·%v Zh·%v G·%d P·%d H·%d <·%d =·%d >·%d M·%d}",
p.baseline0, p.size, p.sizeMiss, p.sizeHalf, p.get, p.put, p.half, p.less, p.equal, p.greater, p.miss)
}
func (p *BufferPool) drain() {
ticker := time.NewTicker(2 * time.Second)
defer ticker.Stop()
for {
select {
case <-ticker.C:
for _, ch := range p.pool {
select {
case <-ch:
default:
}
}
case <-p.closeC:
close(p.closeC)
for _, ch := range p.pool {
close(ch)
}
return
}
}
}
// NewBufferPool creates a new initialized 'buffer pool'.
func NewBufferPool(baseline int) *BufferPool {
if baseline <= 0 {
panic("baseline can't be <= 0")
}
p := &BufferPool{
baseline0: baseline,
baseline: [...]int{baseline / 4, baseline / 2, baseline * 2, baseline * 4},
closeC: make(chan struct{}, 1),
}
for i, cap := range []int{2, 2, 4, 4, 2, 1} {
p.pool[i] = make(chan []byte, cap)
}
go p.drain()
return p
}
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