resource_shared_pool.hpp

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/*
 * Copyright 2008 Search Solution Corporation
 * Copyright 2016 CUBRID Corporation
 *
 *  Licensed 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.
 *
 */

/*
 * resource_shared_pool - template implementation for preallocated shared resources pool & dispatch
 */

#ifndef _RESOURCE_SHARED_POOL_HPP_
#define _RESOURCE_SHARED_POOL_HPP_

#include <mutex>

template <class T>
class resource_shared_pool
{
  public:
    resource_shared_pool (size_t size, bool allow_claimed_on_destruction = false)
      : m_size (size)
      , m_free_stack_size (size)
      , m_mutex ()
      , m_allow_claimed_on_destruction (allow_claimed_on_destruction)
    {
      m_resources = new T [size];
      m_own_resources = m_resources;
      populate_free_stack ();
    }

    resource_shared_pool (T *resources, size_t size, bool allow_claimed_on_destruction = false)
      : m_size (size)
      , m_free_stack_size (size)
      , m_mutex ()
      , m_resources (resources)
      , m_own_resources (NULL)
      , m_free_stack (NULL)
      , m_allow_claimed_on_destruction (allow_claimed_on_destruction)
    {
      populate_free_stack ();
    }

    ~resource_shared_pool ()
    {
      assert (m_allow_claimed_on_destruction || m_free_stack_size == m_size);
      delete [] m_free_stack;
      delete [] m_own_resources;
    }

    inline T *claim (void)
    {
      assert (m_free_stack_size <= m_size);

      std::unique_lock<std::mutex> ulock (m_mutex);
      if (m_free_stack_size == 0)
    {
      return NULL;
    }
      return m_free_stack[--m_free_stack_size];
    }

    inline void retire (T &claimed)
    {
      assert (&claimed >= m_resources && &claimed < m_resources + m_size);
      assert (m_free_stack_size < m_size);

      std::unique_lock<std::mutex> ulock (m_mutex);

      m_free_stack[m_free_stack_size++] = &claimed;
    }

  private:
    resource_shared_pool ();    // no implicit constructor
    resource_shared_pool (const resource_shared_pool &); // no copy constructor

    void populate_free_stack ()
    {
      m_free_stack = new T* [m_size];
      for (size_t i = 0; i < m_free_stack_size; i++)
    {
      m_free_stack[i] = &m_resources[i];
    }
    }

    size_t m_size;
    size_t m_free_stack_size;
    std::mutex m_mutex;

    T *m_resources;
    T *m_own_resources;
    T **m_free_stack;

    bool m_allow_claimed_on_destruction;
};

#endif // _RESOURCE_SHARED_POOL_HPP_