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 8 namespace leveldb { 9 10 static const int kBlockSize = 4096; 11 12 Arena::Arena() { 13 blocks_memory_ = 0; 14 alloc_ptr_ = NULL; // First allocation will allocate a block 15 alloc_bytes_remaining_ = 0; 16 } 17 18 Arena::~Arena() { 19 for (size_t i = 0; i < blocks_.size(); i++) { 20 delete[] blocks_[i]; 21 } 22 } 23 24 char* 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 42 char* Arena::AllocateAligned(size_t bytes) { 43 const int align = sizeof(void*); // We'll align to pointer size 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 61 char* 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
