You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 
rocksdb/util/arena.cc

92 lines
2.9 KiB

// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "util/arena.h"
#include <algorithm>
namespace rocksdb {
const size_t Arena::kMinBlockSize = 4096;
const size_t Arena::kMaxBlockSize = 2 << 30;
static const int kAlignUnit = sizeof(void*);
size_t OptimizeBlockSize(size_t block_size) {
// Make sure block_size is in optimal range
block_size = std::max(Arena::kMinBlockSize, block_size);
block_size = std::min(Arena::kMaxBlockSize, block_size);
// make sure block_size is the multiple of kAlignUnit
if (block_size % kAlignUnit != 0) {
block_size = (1 + block_size / kAlignUnit) * kAlignUnit;
}
return block_size;
}
Arena::Arena(size_t block_size) : kBlockSize(OptimizeBlockSize(block_size)) {
assert(kBlockSize >= kMinBlockSize && kBlockSize <= kMaxBlockSize &&
kBlockSize % kAlignUnit == 0);
}
Arena::~Arena() {
for (const auto& block : blocks_) {
delete[] block;
}
}
char* Arena::AllocateFallback(size_t bytes, bool aligned) {
if (bytes > kBlockSize / 4) {
// Object is more than a quarter of our block size. Allocate it separately
// to avoid wasting too much space in leftover bytes.
return AllocateNewBlock(bytes);
}
// We waste the remaining space in the current block.
auto block_head = AllocateNewBlock(kBlockSize);
alloc_bytes_remaining_ = kBlockSize - bytes;
if (aligned) {
aligned_alloc_ptr_ = block_head + bytes;
unaligned_alloc_ptr_ = block_head + kBlockSize;
return block_head;
} else {
aligned_alloc_ptr_ = block_head;
unaligned_alloc_ptr_ = block_head + kBlockSize - bytes;
return unaligned_alloc_ptr_;
}
}
char* Arena::AllocateAligned(size_t bytes) {
assert((kAlignUnit & (kAlignUnit - 1)) ==
0); // Pointer size should be a power of 2
size_t current_mod =
reinterpret_cast<uintptr_t>(aligned_alloc_ptr_) & (kAlignUnit - 1);
size_t slop = (current_mod == 0 ? 0 : kAlignUnit - current_mod);
size_t needed = bytes + slop;
char* result;
if (needed <= alloc_bytes_remaining_) {
result = aligned_alloc_ptr_ + slop;
aligned_alloc_ptr_ += needed;
alloc_bytes_remaining_ -= needed;
} else {
// AllocateFallback always returned aligned memory
result = AllocateFallback(bytes, true /* aligned */);
}
assert((reinterpret_cast<uintptr_t>(result) & (kAlignUnit - 1)) == 0);
return result;
}
char* Arena::AllocateNewBlock(size_t block_bytes) {
char* block = new char[block_bytes];
blocks_memory_ += block_bytes;
blocks_.push_back(block);
return block;
}
} // namespace rocksdb