// 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.

#ifndef STORAGE_LEVELDB_UTIL_ARENA_H_

#define STORAGE_LEVELDB_UTIL_ARENA_H_

#include <atomic>

#include <cassert>

#include <cstddef>

#include <cstdint>

#include <vector>

namespace leveldb {

class Arena {

 public:

  Arena();

  Arena(const Arena&) = delete;

  Arena& operator=(const Arena&) = delete;

  ~Arena();

  // Return a pointer to a newly allocated memory block of "bytes" bytes.

  char* Allocate(size_t bytes);

  // Allocate memory with the normal alignment guarantees provided by malloc.

  char* AllocateAligned(size_t bytes);

  // Returns an estimate of the total memory usage of data allocated

  // by the arena.

  size_t MemoryUsage() const {

    return memory_usage_.load(std::memory_order_relaxed);

  }

 private:

  char* AllocateFallback(size_t bytes);

  char* AllocateNewBlock(size_t block_bytes);

  // Allocation state

  char* alloc_ptr_;

  size_t alloc_bytes_remaining_;

  // Array of new[] allocated memory blocks

  std::vector<char*> blocks_;

  // Total memory usage of the arena.

  //

  // TODO(costan): This member is accessed via atomics, but the others are

  //               accessed without any locking. Is this OK?

  std::atomic<size_t> memory_usage_;

};

inline char* Arena::Allocate(size_t bytes) {

  // The semantics of what to return are a bit messy if we allow

  // 0-byte allocations, so we disallow them here (we don't need

  // them for our internal use).

  assert(bytes > 0);

  if (bytes <= alloc_bytes_remaining_) {

    char* result = alloc_ptr_;

    alloc_ptr_ += bytes;

    alloc_bytes_remaining_ -= bytes;

    return result;

  }

  return AllocateFallback(bytes);

}

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_UTIL_ARENA_H_