1// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5#include "util/arena.h"
6#include <assert.h>
7
8namespace leveldb {
9
10static const int kBlockSize = 4096;
11
12Arena::Arena() {
13  blocks_memory_ = 0;
14  alloc_ptr_ = NULL;  // First allocation will allocate a block
15  alloc_bytes_remaining_ = 0;
16}
17
18Arena::~Arena() {
19  for (size_t i = 0; i < blocks_.size(); i++) {
20    delete[] blocks_[i];
21  }
22}
23
24char* Arena::AllocateFallback(size_t bytes) {
25  if (bytes > kBlockSize / 4) {
26    // Object is more than a quarter of our block size.  Allocate it separately
27    // to avoid wasting too much space in leftover bytes.
28    char* result = AllocateNewBlock(bytes);
29    return result;
30  }
31
32  // We waste the remaining space in the current block.
33  alloc_ptr_ = AllocateNewBlock(kBlockSize);
34  alloc_bytes_remaining_ = kBlockSize;
35
36  char* result = alloc_ptr_;
37  alloc_ptr_ += bytes;
38  alloc_bytes_remaining_ -= bytes;
39  return result;
40}
41
42char* Arena::AllocateAligned(size_t bytes) {
43  const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
44  assert((align & (align-1)) == 0);   // Pointer size should be a power of 2
45  size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
46  size_t slop = (current_mod == 0 ? 0 : align - current_mod);
47  size_t needed = bytes + slop;
48  char* result;
49  if (needed <= alloc_bytes_remaining_) {
50    result = alloc_ptr_ + slop;
51    alloc_ptr_ += needed;
52    alloc_bytes_remaining_ -= needed;
53  } else {
54    // AllocateFallback always returned aligned memory
55    result = AllocateFallback(bytes);
56  }
57  assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
58  return result;
59}
60
61char* Arena::AllocateNewBlock(size_t block_bytes) {
62  char* result = new char[block_bytes];
63  blocks_memory_ += block_bytes;
64  blocks_.push_back(result);
65  return result;
66}
67
68}  // namespace leveldb
69