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// 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"
namespace leveldb {
static const int kBlockSize = 4096;
Arena::Arena()
: alloc_ptr_(nullptr), alloc_bytes_remaining_(0), memory_usage_(0) {}
Arena::~Arena() {
for (size_t i = 0; i < blocks_.size(); i++) {
delete[] blocks_[i];
}
}
char* Arena::AllocateFallback(size_t bytes) {
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.
char* result = AllocateNewBlock(bytes);
return result;
}
// We waste the remaining space in the current block.
alloc_ptr_ = AllocateNewBlock(kBlockSize);
alloc_bytes_remaining_ = kBlockSize;
char* result = alloc_ptr_;
alloc_ptr_ += bytes;
alloc_bytes_remaining_ -= bytes;
return result;
}
char* Arena::AllocateAligned(size_t bytes) {
const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
static_assert((align & (align - 1)) == 0,
"Pointer size should be a power of 2");
size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align - 1);
size_t slop = (current_mod == 0 ? 0 : align - current_mod);
size_t needed = bytes + slop;
char* result;
if (needed <= alloc_bytes_remaining_) {
result = alloc_ptr_ + slop;
alloc_ptr_ += needed;
alloc_bytes_remaining_ -= needed;
} else {
// AllocateFallback always returned aligned memory
result = AllocateFallback(bytes);
}
assert((reinterpret_cast<uintptr_t>(result) & (align - 1)) == 0);
return result;
}
char* Arena::AllocateNewBlock(size_t block_bytes) {
char* result = new char[block_bytes];
blocks_.push_back(result);
memory_usage_.fetch_add(block_bytes + sizeof(char*),
std::memory_order_relaxed);
return result;
}
} // namespace leveldb
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