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pool.go
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pool.go
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package bytebufferpool
import (
"sort"
"sync"
"sync/atomic"
)
const (
minBitSize = 6
steps = 20
minSize = 1 << minBitSize
maxSize = 1 << (minBitSize + steps - 1)
calibrateCallsThreshold = 42000
maxPercentile = 0.95
)
type byteBufferPool struct {
calls [steps]uint64
calibrating uint64
defaultSize uint64
maxSize uint64
pool sync.Pool
}
func (p *byteBufferPool) Acquire() *ByteBuffer {
v := p.pool.Get()
if v != nil {
return v.(*ByteBuffer)
}
return &ByteBuffer{
B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
}
}
func (p *byteBufferPool) Release(b *ByteBuffer) {
idx := bitSize(len(b.B)-1) - minBitSize
if idx < 0 {
idx = 0
} else if idx >= steps {
idx = steps - 1
}
if atomic.AddUint64(&p.calls[idx], 1) > calibrateCallsThreshold {
p.calibrate()
}
maxSize := int(atomic.LoadUint64(&p.maxSize))
if maxSize > 0 && cap(b.B) <= maxSize {
b.B = b.B[:0]
p.pool.Put(b)
}
}
func (p *byteBufferPool) calibrate() {
if !atomic.CompareAndSwapUint64(&p.calibrating, 0, 1) {
return
}
a := make(callSizes, 0, steps)
var callsSum uint64
for i := uint64(0); i < steps; i++ {
calls := atomic.SwapUint64(&p.calls[i], 0)
callsSum += calls
a = append(a, callSize{
calls: calls,
size: minSize << i,
})
}
sort.Sort(a)
defaultSize := a[0].size
maxSize := defaultSize
maxSum := uint64(float64(callsSum) * maxPercentile)
callsSum = 0
for i := 0; i < steps; i++ {
if callsSum > maxSum {
break
}
callsSum += a[i].calls
size := a[i].size
if size > maxSize {
maxSize = size
}
}
atomic.StoreUint64(&p.defaultSize, defaultSize)
atomic.StoreUint64(&p.maxSize, maxSize)
atomic.StoreUint64(&p.calibrating, 0)
}
type callSize struct {
calls uint64
size uint64
}
type callSizes []callSize
func (ci callSizes) Len() int {
return len(ci)
}
func (ci callSizes) Less(i, j int) bool {
return ci[i].calls > ci[j].calls
}
func (ci callSizes) Swap(i, j int) {
ci[i], ci[j] = ci[j], ci[i]
}
func bitSize(n int) int {
s := 0
for n > 0 {
n >>= 1
s++
}
return s
}