// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements.  See the NOTICE file

// distributed with this work for additional information

// regarding copyright ownership.  The ASF licenses this file

// to you under the Apache License, Version 2.0 (the

// "License"); you may not use this file except in compliance

// with the License.  You may obtain a copy of the License at

//

//   http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing,

// software distributed under the License is distributed on an

// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

// KIND, either express or implied.  See the License for the

// specific language governing permissions and limitations

// under the License.

// Date: Fri Jun  5 18:25:40 CST 2015

// Do small memory allocations on continuous blocks.

#ifndef BUTIL_ARENA_H

#define BUTIL_ARENA_H

#include <stdint.h>

#include "butil/macros.h"

namespace butil {

struct ArenaOptions {

    size_t initial_block_size;

    size_t max_block_size;

    // Constructed with default options.

    ArenaOptions();

};

// Just a proof-of-concept, will be refactored in future CI.

class Arena {

public:

    explicit Arena(const ArenaOptions& options = ArenaOptions());

    ~Arena();

    void swap(Arena&);

    void* allocate(size_t n);

    void* allocate_aligned(size_t n);  // not implemented.

    void clear();

private:

    DISALLOW_COPY_AND_ASSIGN(Arena);

    struct Block {

        uint32_t left_space() const { return size - alloc_size; }

        Block* next;

        uint32_t alloc_size;

        uint32_t size;

        char data[0];

    };

    void* allocate_in_other_blocks(size_t n);

    void* allocate_new_block(size_t n);

    Block* pop_block(Block* & head) {

        Block* saved_head = head;

        head = head->next;

        return saved_head;

    }

    Block* _cur_block;

    Block* _isolated_blocks;

    size_t _block_size;

    ArenaOptions _options;

};

inline void* Arena::allocate(size_t n) {

    if (_cur_block != NULL && _cur_block->left_space() >= n) {

        void* ret = _cur_block->data + _cur_block->alloc_size;

        _cur_block->alloc_size += n;

        return ret;

    }

    return allocate_in_other_blocks(n);

}

}  // namespace butil

#endif  // BUTIL_ARENA_H