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package bytebufferpool
import (
"sort"
"sync"
"sync/atomic"
)
const (
minBitSize = 6 // 2**6=64 is a CPU cache line size
steps = 20
minSize = 1 << minBitSize
maxSize = 1 << (minBitSize + steps - 1)
calibrateCallsThreshold = 42000
maxPercentile = 0.95
)
// Pool represents byte buffer pool.
//
// Distinct pools may be used for distinct types of byte buffers.
// Properly determined byte buffer types with their own pools may help reducing
// memory waste.
type Pool struct {
calls [steps]uint64
calibrating uint64
defaultSize uint64
maxSize uint64
pool sync.Pool
}
var defaultPool Pool
// Get returns an empty byte buffer from the pool.
//
// Got byte buffer may be returned to the pool via Put call.
// This reduces the number of memory allocations required for byte buffer
// management.
func Get() *ByteBuffer { return defaultPool.Get() }
// Get returns new byte buffer with zero length.
//
// The byte buffer may be returned to the pool via Put after the use
// in order to minimize GC overhead.
func (p *Pool) Get() *ByteBuffer {
v := p.pool.Get()
if v != nil {
return v.(*ByteBuffer)
}
return &ByteBuffer{
B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
}
}
// Put returns byte buffer to the pool.
//
// ByteBuffer.B mustn't be touched after returning it to the pool.
// Otherwise data races will occur.
func Put(b *ByteBuffer) { defaultPool.Put(b) }
// Put releases byte buffer obtained via Get to the pool.
//
// The buffer mustn't be accessed after returning to the pool.
func (p *Pool) Put(b *ByteBuffer) {
idx := index(len(b.B))
if atomic.AddUint64(&p.calls[idx], 1) > calibrateCallsThreshold {
p.calibrate()
}
maxSize := int(atomic.LoadUint64(&p.maxSize))
if maxSize == 0 || cap(b.B) <= maxSize {
b.Reset()
p.pool.Put(b)
}
}
func (p *Pool) 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 index(n int) int {
n--
n >>= minBitSize
idx := 0
for n > 0 {
n >>= 1
idx++
}
if idx >= steps {
idx = steps - 1
}
return idx
}
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