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 Arena()12Arena::Arena() : memory_usage_(0) { 13 alloc_ptr_ = NULL; // First allocation will allocate a block 14 alloc_bytes_remaining_ = 0; 15 } 16 ~Arena()17Arena::~Arena() { 18 for (size_t i = 0; i < blocks_.size(); i++) { 19 delete[] blocks_[i]; 20 } 21 } 22 AllocateFallback(size_t bytes)23char* Arena::AllocateFallback(size_t bytes) { 24 if (bytes > kBlockSize / 4) { 25 // Object is more than a quarter of our block size. Allocate it separately 26 // to avoid wasting too much space in leftover bytes. 27 char* result = AllocateNewBlock(bytes); 28 return result; 29 } 30 31 // We waste the remaining space in the current block. 32 alloc_ptr_ = AllocateNewBlock(kBlockSize); 33 alloc_bytes_remaining_ = kBlockSize; 34 35 char* result = alloc_ptr_; 36 alloc_ptr_ += bytes; 37 alloc_bytes_remaining_ -= bytes; 38 return result; 39 } 40 AllocateAligned(size_t bytes)41char* Arena::AllocateAligned(size_t bytes) { 42 const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8; 43 assert((align & (align-1)) == 0); // Pointer size should be a power of 2 44 size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1); 45 size_t slop = (current_mod == 0 ? 0 : align - current_mod); 46 size_t needed = bytes + slop; 47 char* result; 48 if (needed <= alloc_bytes_remaining_) { 49 result = alloc_ptr_ + slop; 50 alloc_ptr_ += needed; 51 alloc_bytes_remaining_ -= needed; 52 } else { 53 // AllocateFallback always returned aligned memory 54 result = AllocateFallback(bytes); 55 } 56 assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0); 57 return result; 58 } 59 AllocateNewBlock(size_t block_bytes)60char* Arena::AllocateNewBlock(size_t block_bytes) { 61 char* result = new char[block_bytes]; 62 blocks_.push_back(result); 63 memory_usage_.NoBarrier_Store( 64 reinterpret_cast<void*>(MemoryUsage() + block_bytes + sizeof(char*))); 65 return result; 66 } 67 68 } // namespace leveldb 69