prometheus/vendor/github.com/mailru/easyjson/buffer/pool.go
2016-10-17 10:32:10 +02:00

208 lines
4.1 KiB
Go

// Package buffer implements a buffer for serialization, consisting of a chain of []byte-s to
// reduce copying and to allow reuse of individual chunks.
package buffer
import (
"io"
"sync"
)
// PoolConfig contains configuration for the allocation and reuse strategy.
type PoolConfig struct {
StartSize int // Minimum chunk size that is allocated.
PooledSize int // Minimum chunk size that is reused, reusing chunks too small will result in overhead.
MaxSize int // Maximum chunk size that will be allocated.
}
var config = PoolConfig{
StartSize: 128,
PooledSize: 512,
MaxSize: 32768,
}
// Reuse pool: chunk size -> pool.
var buffers = map[int]*sync.Pool{}
func initBuffers() {
for l := config.PooledSize; l <= config.MaxSize; l *= 2 {
buffers[l] = new(sync.Pool)
}
}
func init() {
initBuffers()
}
// Init sets up a non-default pooling and allocation strategy. Should be run before serialization is done.
func Init(cfg PoolConfig) {
config = cfg
initBuffers()
}
// putBuf puts a chunk to reuse pool if it can be reused.
func putBuf(buf []byte) {
size := cap(buf)
if size < config.PooledSize {
return
}
if c := buffers[size]; c != nil {
c.Put(buf[:0])
}
}
// getBuf gets a chunk from reuse pool or creates a new one if reuse failed.
func getBuf(size int) []byte {
if size < config.PooledSize {
return make([]byte, 0, size)
}
if c := buffers[size]; c != nil {
v := c.Get()
if v != nil {
return v.([]byte)
}
}
return make([]byte, 0, size)
}
// Buffer is a buffer optimized for serialization without extra copying.
type Buffer struct {
// Buf is the current chunk that can be used for serialization.
Buf []byte
toPool []byte
bufs [][]byte
}
// EnsureSpace makes sure that the current chunk contains at least s free bytes,
// possibly creating a new chunk.
func (b *Buffer) EnsureSpace(s int) {
if cap(b.Buf)-len(b.Buf) >= s {
return
}
l := len(b.Buf)
if l > 0 {
if cap(b.toPool) != cap(b.Buf) {
// Chunk was reallocated, toPool can be pooled.
putBuf(b.toPool)
}
if cap(b.bufs) == 0 {
b.bufs = make([][]byte, 0, 8)
}
b.bufs = append(b.bufs, b.Buf)
l = cap(b.toPool) * 2
} else {
l = config.StartSize
}
if l > config.MaxSize {
l = config.MaxSize
}
b.Buf = getBuf(l)
b.toPool = b.Buf
}
// AppendByte appends a single byte to buffer.
func (b *Buffer) AppendByte(data byte) {
if cap(b.Buf) == len(b.Buf) { // EnsureSpace won't be inlined.
b.EnsureSpace(1)
}
b.Buf = append(b.Buf, data)
}
// AppendBytes appends a byte slice to buffer.
func (b *Buffer) AppendBytes(data []byte) {
for len(data) > 0 {
if cap(b.Buf) == len(b.Buf) { // EnsureSpace won't be inlined.
b.EnsureSpace(1)
}
sz := cap(b.Buf) - len(b.Buf)
if sz > len(data) {
sz = len(data)
}
b.Buf = append(b.Buf, data[:sz]...)
data = data[sz:]
}
}
// AppendBytes appends a string to buffer.
func (b *Buffer) AppendString(data string) {
for len(data) > 0 {
if cap(b.Buf) == len(b.Buf) { // EnsureSpace won't be inlined.
b.EnsureSpace(1)
}
sz := cap(b.Buf) - len(b.Buf)
if sz > len(data) {
sz = len(data)
}
b.Buf = append(b.Buf, data[:sz]...)
data = data[sz:]
}
}
// Size computes the size of a buffer by adding sizes of every chunk.
func (b *Buffer) Size() int {
size := len(b.Buf)
for _, buf := range b.bufs {
size += len(buf)
}
return size
}
// DumpTo outputs the contents of a buffer to a writer and resets the buffer.
func (b *Buffer) DumpTo(w io.Writer) (written int, err error) {
var n int
for _, buf := range b.bufs {
if err == nil {
n, err = w.Write(buf)
written += n
}
putBuf(buf)
}
if err == nil {
n, err = w.Write(b.Buf)
written += n
}
putBuf(b.toPool)
b.bufs = nil
b.Buf = nil
b.toPool = nil
return
}
// BuildBytes creates a single byte slice with all the contents of the buffer. Data is
// copied if it does not fit in a single chunk.
func (b *Buffer) BuildBytes() []byte {
if len(b.bufs) == 0 {
ret := b.Buf
b.toPool = nil
b.Buf = nil
return ret
}
ret := make([]byte, 0, b.Size())
for _, buf := range b.bufs {
ret = append(ret, buf...)
putBuf(buf)
}
ret = append(ret, b.Buf...)
putBuf(b.toPool)
b.bufs = nil
b.toPool = nil
b.Buf = nil
return ret
}