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
7namespace leveldb {
8
9static const int kBlockSize = 4096;
10
11Arena::Arena()
12 : alloc_ptr_(nullptr), alloc_bytes_remaining_(0), memory_usage_(0) {}
13
14Arena::~Arena() {
15 for (size_t i = 0; i < blocks_.size(); i++) {
16 delete[] blocks_[i];
17 }
18}
19
20char* Arena::AllocateFallback(size_t bytes) {
21 if (bytes > kBlockSize / 4) {
22 // Object is more than a quarter of our block size. Allocate it separately
23 // to avoid wasting too much space in leftover bytes.
24 char* result = AllocateNewBlock(bytes);
25 return result;
26 }
27
28 // We waste the remaining space in the current block.
29 alloc_ptr_ = AllocateNewBlock(kBlockSize);
30 alloc_bytes_remaining_ = kBlockSize;
31
32 char* result = alloc_ptr_;
33 alloc_ptr_ += bytes;
34 alloc_bytes_remaining_ -= bytes;
35 return result;
36}
37
38char* Arena::AllocateAligned(size_t bytes) {
39 const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
40 static_assert((align & (align - 1)) == 0,
41 "Pointer size should be a power of 2");
42 size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align - 1);
43 size_t slop = (current_mod == 0 ? 0 : align - current_mod);
44 size_t needed = bytes + slop;
45 char* result;
46 if (needed <= alloc_bytes_remaining_) {
47 result = alloc_ptr_ + slop;
48 alloc_ptr_ += needed;
49 alloc_bytes_remaining_ -= needed;
50 } else {
51 // AllocateFallback always returned aligned memory
52 result = AllocateFallback(bytes);
53 }
54 assert((reinterpret_cast<uintptr_t>(result) & (align - 1)) == 0);
55 return result;
56}
57
58char* Arena::AllocateNewBlock(size_t block_bytes) {
59 char* result = new char[block_bytes];
60 blocks_.push_back(result);
61 memory_usage_.fetch_add(block_bytes + sizeof(char*),
62 std::memory_order_relaxed);
63 return result;
64}
65
66} // namespace leveldb
67