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80 lines
2.2 KiB
80 lines
2.2 KiB
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package arena
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// Allocator pre-allocates memory to reduce memory allocation cost.
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// It is not thread-safe.
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type Allocator interface {
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// Alloc allocates memory with 0 len and capacity cap.
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Alloc(capacity int) []byte
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// AllocWithLen allocates memory with length and capacity.
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AllocWithLen(length int, capacity int) []byte
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// Reset resets arena offset.
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// Make sure all the allocated memory are not used any more.
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Reset()
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}
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// SimpleAllocator is a simple implementation of ArenaAllocator.
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type SimpleAllocator struct {
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arena []byte
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off int
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}
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type stdAllocator struct {
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}
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func (a *stdAllocator) Alloc(capacity int) []byte {
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return make([]byte, 0, capacity)
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}
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func (a *stdAllocator) AllocWithLen(length int, capacity int) []byte {
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return make([]byte, length, capacity)
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}
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func (a *stdAllocator) Reset() {
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}
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var _ Allocator = &stdAllocator{}
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// StdAllocator implements Allocator but do not pre-allocate memory.
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var StdAllocator = &stdAllocator{}
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// NewAllocator creates an Allocator with a specified capacity.
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func NewAllocator(capacity int) *SimpleAllocator {
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return &SimpleAllocator{arena: make([]byte, 0, capacity)}
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}
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// Alloc implements Allocator.AllocBytes interface.
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func (s *SimpleAllocator) Alloc(capacity int) []byte {
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if s.off+capacity < cap(s.arena) {
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slice := s.arena[s.off : s.off : s.off+capacity]
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s.off += capacity
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return slice
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}
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return make([]byte, 0, capacity)
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}
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// AllocWithLen implements Allocator.AllocWithLen interface.
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func (s *SimpleAllocator) AllocWithLen(length int, capacity int) []byte {
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slice := s.Alloc(capacity)
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return slice[:length:capacity]
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}
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// Reset implements Allocator.Reset interface.
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func (s *SimpleAllocator) Reset() {
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s.off = 0
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}
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