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 | |
7 | namespace leveldb { |
8 | |
9 | static const int kBlockSize = 4096; |
10 | |
11 | Arena::Arena() |
12 | : alloc_ptr_(nullptr), alloc_bytes_remaining_(0), memory_usage_(0) {} |
13 | |
14 | Arena::~Arena() { |
15 | for (size_t i = 0; i < blocks_.size(); i++) { |
16 | delete[] blocks_[i]; |
17 | } |
18 | } |
19 | |
20 | char* 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 | |
38 | char* 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 | |
58 | char* 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 |