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// Package iobufpool implements a global segregated-fit pool of buffers for IO.
//
// It uses *[]byte instead of []byte to avoid the sync.Pool allocation with Put. Unfortunately, using a pointer to avoid
// an allocation is purposely not documented. https://github.com/golang/go/issues/16323
package iobufpool
import "sync"
const minPoolExpOf2 = 8
var pools [18]*sync.Pool
func init() {
for i := range pools {
bufLen := 1 << (minPoolExpOf2 + i)
pools[i] = &sync.Pool{
New: func() any {
buf := make([]byte, bufLen)
return &buf
},
}
}
}
// Get gets a []byte of len size with cap <= size*2.
func Get(size int) *[]byte {
i := getPoolIdx(size)
if i >= len(pools) {
buf := make([]byte, size)
return &buf
}
ptrBuf := (pools[i].Get().(*[]byte))
*ptrBuf = (*ptrBuf)[:size]
return ptrBuf
}
func getPoolIdx(size int) int {
size--
size >>= minPoolExpOf2
i := 0
for size > 0 {
size >>= 1
i++
}
return i
}
// Put returns buf to the pool.
func Put(buf *[]byte) {
i := putPoolIdx(cap(*buf))
if i < 0 {
return
}
pools[i].Put(buf)
}
func putPoolIdx(size int) int {
minPoolSize := 1 << minPoolExpOf2
for i := range pools {
if size == minPoolSize<<i {
return i
}
}
return -1
}
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