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bytebuffer.go
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bytebuffer.go
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package utils
import (
"io"
"sort"
"sync"
"sync/atomic"
)
// ByteBuffer provides byte buffer, which can be used for minimizing
// memory allocations.
//
// ByteBuffer may be used with functions appending data to the given []byte
// slice. See example code for details.
//
// Use Get for obtaining an empty byte buffer.
type ByteBuffer struct {
// B is a byte buffer to use in append-like workloads.
// See example code for details.
B []byte
}
// Len returns the size of the byte buffer.
func (b *ByteBuffer) Len() int {
return len(b.B)
}
// ReadFrom implements io.ReaderFrom.
//
// The function appends all the data read from r to b.
func (b *ByteBuffer) ReadFrom(r io.Reader) (int64, error) {
p := b.B
nStart := int64(len(p))
nMax := int64(cap(p))
n := nStart
if nMax == 0 {
nMax = 64
p = make([]byte, nMax)
} else {
p = p[:nMax]
}
for {
if n == nMax {
nMax *= 2
bNew := make([]byte, nMax)
copy(bNew, p)
p = bNew
}
nn, err := r.Read(p[n:])
n += int64(nn)
if err != nil {
b.B = p[:n]
n -= nStart
if err == io.EOF {
return n, nil
}
return n, err
}
}
}
// Bytes returns b.B, i.e. all the bytes accumulated in the buffer.
//
// The purpose of this function is bytes.Buffer compatibility.
func (b *ByteBuffer) Bytes() []byte {
return b.B
}
// Write implements io.Writer - it appends p to ByteBuffer.B
func (b *ByteBuffer) Write(p []byte) (int, error) {
b.B = append(b.B, p...)
return len(p), nil
}
// WriteByte appends the byte c to the buffer.
//
// The purpose of this function is bytes.Buffer compatibility.
//
// The function always returns nil.
func (b *ByteBuffer) WriteByte(c byte) error {
b.B = append(b.B, c)
return nil
}
// WriteString appends s to ByteBuffer.B.
func (b *ByteBuffer) WriteString(s string) (int, error) {
b.B = append(b.B, s...)
return len(s), nil
}
// Set sets ByteBuffer.B to p.
func (b *ByteBuffer) Set(p []byte) {
b.B = append(b.B[:0], p...)
}
// SetString sets ByteBuffer.B to s.
func (b *ByteBuffer) SetString(s string) {
b.B = append(b.B[:0], s...)
}
// String returns string representation of ByteBuffer.B.
func (b *ByteBuffer) String() string {
return string(b.B)
}
// Reset makes ByteBuffer.B empty.
func (b *ByteBuffer) Reset() {
b.B = b.B[:0]
}
// ChangeLen changes the buffer length.
func (b *ByteBuffer) ChangeLen(newLen int) {
if cap(b.B) < newLen {
b.B = make([]byte, newLen)
} else {
b.B = b.B[:newLen]
}
}
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
)
// BufferPool 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 BufferPool struct {
calls [steps]uint64
calibrating uint64
defaultSize uint64
maxSize uint64
pool sync.Pool
}
var defaultBufferPool BufferPool
// AcquireByteBuffer 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 AcquireByteBuffer() *ByteBuffer { return defaultBufferPool.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 *BufferPool) Get() *ByteBuffer {
v := p.pool.Get()
if v != nil {
return v.(*ByteBuffer)
}
return &ByteBuffer{
B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
}
}
// ReleaseByteBuffer returns byte buffer to the pool.
//
// ByteBuffer.B mustn't be touched after returning it to the pool.
// Otherwise data races will occur.
func ReleaseByteBuffer(b *ByteBuffer) { defaultBufferPool.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 *BufferPool) 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 *BufferPool) 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
}