// 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