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allocator.go
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allocator.go
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// Copyright (C) 2020-2021, IrineSistiana
//
// This file is part of mosdns.
//
// mosdns is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// mosdns is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
// This file is a modified version from https://github.com/xtaci/smux/blob/master/alloc.go f386d90
// license of smux: MIT https://github.com/xtaci/smux/blob/master/LICENSE
package pool
import (
"fmt"
"math/bits"
"sync"
)
const (
// Since go 1.15, the go memory allocator is much more faster than a sync.Pool
// when allocating small object.
ignoreSmallObj = 64
)
var (
// allocator is an Allocator with 1 Megabyte maximum reusable buf size limit (1<<20).
allocator = NewAllocator(20)
)
// GetBuf returns a buf from a global allocator.
// The reuse limit is 1 Megabytes.
func GetBuf(size int) []byte {
return allocator.Get(size)
}
// ReleaseBuf releases the b
func ReleaseBuf(b []byte) {
allocator.Release(b)
}
type Allocator struct {
maxPoolLen int
buffers []sync.Pool
}
// NewAllocator initiates a []byte allocatorL.
// []byte that has less than 1 << maxPoolBitsLen bytes is managed by sync.Pool.
// The waste(memory fragmentation) of space allocation is guaranteed to be
// no more than 50%.
func NewAllocator(maxPoolBitsLen int) *Allocator {
alloc := &Allocator{
maxPoolLen: 1 << maxPoolBitsLen,
buffers: make([]sync.Pool, maxPoolBitsLen+1),
}
for i := range alloc.buffers {
bufSize := 1 << uint32(i)
alloc.buffers[i].New = func() interface{} {
return make([]byte, bufSize)
}
}
return alloc
}
// Get returns a []byte from pool with most appropriate cap
func (alloc *Allocator) Get(size int) []byte {
if size <= 0 {
panic(fmt.Sprintf("Allocator Get: negtive slice size %d", size))
}
if size > alloc.maxPoolLen || size <= ignoreSmallObj {
return make([]byte, size)
}
i := shard(size)
return alloc.buffers[i].Get().([]byte)[:size]
}
// Release releases the buf to the allocatorL.
func (alloc *Allocator) Release(buf []byte) {
if cap(buf) > alloc.maxPoolLen || cap(buf) <= ignoreSmallObj {
return
}
i := shard(cap(buf))
if cap(buf) == 0 || cap(buf) > alloc.maxPoolLen || cap(buf) != 1<<i {
panic("unexpected cap size")
}
alloc.buffers[i].Put(buf)
}
// shard returns the shard index that is suitable for the size.
func shard(size int) int {
if size <= 1 {
return 0
}
return bits.Len64(uint64(size - 1))
}