// 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