tidb arena 源码
tidb arena 代码
文件路径：/util/arena/arena.go
// Copyright 2015 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package arena
// Allocator pre-allocates memory to reduce memory allocation cost.
// It is not thread-safe.
type Allocator interface {
// Alloc allocates memory with 0 len and capacity cap.
Alloc(capacity int) []byte
// AllocWithLen allocates memory with length and capacity.
AllocWithLen(length int, capacity int) []byte
// Reset resets arena offset.
// Make sure all the allocated memory are not used any more.
Reset()
}
// SimpleAllocator is a simple implementation of ArenaAllocator.
type SimpleAllocator struct {
arena []byte
off int
}
type stdAllocator struct {
}
func (*stdAllocator) Alloc(capacity int) []byte {
return make([]byte, 0, capacity)
}
func (*stdAllocator) AllocWithLen(length int, capacity int) []byte {
return make([]byte, length, capacity)
}
func (*stdAllocator) Reset() {}
var _ Allocator = &stdAllocator{}
// StdAllocator implements Allocator but do not pre-allocate memory.
var StdAllocator = &stdAllocator{}
// NewAllocator creates an Allocator with a specified capacity.
func NewAllocator(capacity int) *SimpleAllocator {
return &SimpleAllocator{arena: make([]byte, 0, capacity)}
}
// Alloc implements Allocator.AllocBytes interface.
func (s *SimpleAllocator) Alloc(capacity int) []byte {
if s.off+capacity < cap(s.arena) {
slice := s.arena[s.off : s.off : s.off+capacity]
s.off += capacity
return slice
}
return make([]byte, 0, capacity)
}
// AllocWithLen implements Allocator.AllocWithLen interface.
func (s *SimpleAllocator) AllocWithLen(length int, capacity int) []byte {
slice := s.Alloc(capacity)
return slice[:length:capacity]
}
// Reset implements Allocator.Reset interface.
func (s *SimpleAllocator) Reset() {
s.off = 0
}
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