152 lines
2.9 KiB
Go
152 lines
2.9 KiB
Go
package bytebufferpool
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import (
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"sort"
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"sync"
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"sync/atomic"
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)
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const (
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minBitSize = 6 // 2**6=64 is a CPU cache line size
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steps = 20
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minSize = 1 << minBitSize
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maxSize = 1 << (minBitSize + steps - 1)
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calibrateCallsThreshold = 42000
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maxPercentile = 0.95
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)
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// Pool represents byte buffer pool.
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//
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// Distinct pools may be used for distinct types of byte buffers.
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// Properly determined byte buffer types with their own pools may help reducing
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// memory waste.
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type Pool struct {
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calls [steps]uint64
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calibrating uint64
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defaultSize uint64
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maxSize uint64
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pool sync.Pool
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}
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var defaultPool Pool
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// Get returns an empty byte buffer from the pool.
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//
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// Got byte buffer may be returned to the pool via Put call.
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// This reduces the number of memory allocations required for byte buffer
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// management.
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func Get() *ByteBuffer { return defaultPool.Get() }
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// Get returns new byte buffer with zero length.
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//
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// The byte buffer may be returned to the pool via Put after the use
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// in order to minimize GC overhead.
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func (p *Pool) Get() *ByteBuffer {
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v := p.pool.Get()
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if v != nil {
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return v.(*ByteBuffer)
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}
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return &ByteBuffer{
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B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
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}
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}
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// Put returns byte buffer to the pool.
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//
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// ByteBuffer.B mustn't be touched after returning it to the pool.
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// Otherwise data races will occur.
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func Put(b *ByteBuffer) { defaultPool.Put(b) }
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// Put releases byte buffer obtained via Get to the pool.
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//
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// The buffer mustn't be accessed after returning to the pool.
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func (p *Pool) Put(b *ByteBuffer) {
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idx := index(len(b.B))
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if atomic.AddUint64(&p.calls[idx], 1) > calibrateCallsThreshold {
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p.calibrate()
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}
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maxSize := int(atomic.LoadUint64(&p.maxSize))
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if maxSize == 0 || cap(b.B) <= maxSize {
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b.Reset()
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p.pool.Put(b)
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}
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}
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func (p *Pool) calibrate() {
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if !atomic.CompareAndSwapUint64(&p.calibrating, 0, 1) {
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return
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}
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a := make(callSizes, 0, steps)
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var callsSum uint64
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for i := uint64(0); i < steps; i++ {
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calls := atomic.SwapUint64(&p.calls[i], 0)
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callsSum += calls
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a = append(a, callSize{
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calls: calls,
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size: minSize << i,
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})
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}
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sort.Sort(a)
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defaultSize := a[0].size
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maxSize := defaultSize
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maxSum := uint64(float64(callsSum) * maxPercentile)
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callsSum = 0
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for i := 0; i < steps; i++ {
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if callsSum > maxSum {
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break
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}
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callsSum += a[i].calls
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size := a[i].size
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if size > maxSize {
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maxSize = size
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}
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}
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atomic.StoreUint64(&p.defaultSize, defaultSize)
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atomic.StoreUint64(&p.maxSize, maxSize)
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atomic.StoreUint64(&p.calibrating, 0)
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}
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type callSize struct {
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calls uint64
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size uint64
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}
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type callSizes []callSize
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func (ci callSizes) Len() int {
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return len(ci)
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}
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func (ci callSizes) Less(i, j int) bool {
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return ci[i].calls > ci[j].calls
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}
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func (ci callSizes) Swap(i, j int) {
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ci[i], ci[j] = ci[j], ci[i]
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}
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func index(n int) int {
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n--
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n >>= minBitSize
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idx := 0
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for n > 0 {
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n >>= 1
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idx++
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}
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if idx >= steps {
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idx = steps - 1
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}
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return idx
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}
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