fixedAllocator.h

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/**
 *
 *   Copyright 2005-2020 Pierre-Henri WUILLEMIN(@LIP6) & Christophe GONZALES(@AMU)
 *   info_at_agrum_dot_org
 *
 *  This library is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */


/**
 * @file
 * @brief Headers of gum::FixedAllocator
 *
 * @author Pierre-Henri WUILLEMIN(@LIP6) and Jean-Christophe MAGNAN and Christophe
 * GONZALES(@AMU)
 *
 */
#ifndef GUM_FIXED_ALLOCATOR_H
#define GUM_FIXED_ALLOCATOR_H

// ============================================================================
#include <mutex>
#include <thread>
// ============================================================================
#include <agrum/agrum.h>
// ============================================================================

namespace gum {
  /**
   * @class FixedAllocator
   * @headerfile fixedAllocator.h <agrum/tools/core/fixedAllocator.h>
   *
   * @brief Allocates objects of one given size
   *
   * Fixed allocator knows how to allocate and deallocate blocks of fixed size
   * but is not limited to a chunck size. Its capacity is limited only by the
   * available memory.
   * To achieve this, FixedAllocator aggregates a vector of Chunk objects.
   * Whenever an allocation request occurs, FixedAllocators looks for a Chunk
   * that can accomodate the request.
   * If all Chunks are filled up, FixedAllocator appends a new Chunk.
   *
   * @ingroup core
   */

  class FixedAllocator {
    // clang-format off
    /**
     * @struct Chunk__ fixedAllocator.h <agrum/tools/core/smallobjectallocator/fixedAllocator.h>
     *
     * @brief Allocates objects of one given size. Has a fixed limit of
     * allocation
     *
     * Each object of type Chunk contains and manages a chunk of memory
     * containing a
     * amount of blocks. At construction time, you configure the block size and
     * the
     * number of blocks.
     * A Chunk contains logic that allows you to allocate and deallocate memory
     * blocks
     * from that chunk of memory. When there are no more blocks available in the
     * chunk,
     * the allocation function returns zero.
     *
     * @ingroup core
     */
    // clang-format on
    struct Chunk__ {
      // ============================================================================
      /// Initializes a Chunk object
      // ============================================================================
      void init__(const std::size_t& blockSize, const unsigned char& numBlocks);

      // ============================================================================
      /// Allocates a block of memory
      // ============================================================================
      void* allocate__(const std::size_t& blockSize);

      // ============================================================================
      /// Deallocates a block of memory
      // ============================================================================
      void deallocat__(void* p, const std::size_t& blockSize);

      // ============================================================================
      /// Releases the allocated memory
      // ============================================================================
      void release__();

      // ============================================================================
      /// Pointer to the managed memory itself
      // ============================================================================
      unsigned char* pData__;

      // ============================================================================
      /// Holds the index of the first block available in this chunck
      // ============================================================================
      unsigned char firstAvailableBlock__;

      // ============================================================================
      /// Number of blocks available in this chunck
      // ============================================================================
      unsigned char blocksAvailable__;
    };

    public:
    // ############################################################################
    /// @name Constructors / Destructors
    // ############################################################################
    /// @{

    // ============================================================================
    /**
     * Constructor.
     * @param blockSize is the size of an allocated block.
     * @param numBlocks is the number of block allocated per chunk
     * numBlock * blockSize is the size that a chunk allocates directly
     * when it is created
     */
    // ============================================================================
    FixedAllocator(const std::size_t&   blockSize,
                   const unsigned char& numBlocks = UCHAR_MAX);

    // ============================================================================
    /// Destructor.
    // ============================================================================
    ~FixedAllocator();

    /// @}

    // ############################################################################
    /// @name Allocator / Deallocator
    // ############################################################################
    /// @{

    // ============================================================================
    /// Allocates a block
    // ============================================================================
    void* allocate();

    // ============================================================================
    /// Deallocates a block
    // ============================================================================
    void deallocate(void* pDeallocatedBlock);

    /// @}

    // ============================================================================
    /// Returns the size of block allocated by this FixedAllocator
    // ============================================================================
    const size_t& objectSize() { return blockSize__; }

    private:
    // ============================================================================
    /// Size of a memory block allocated
    // ============================================================================
    std::size_t blockSize__;

    // ============================================================================
    /// The maximum number of blocks a chunk can allocate
    // ============================================================================
    unsigned char numBlocks__;

    // ============================================================================
    /// Vector of Chunk__ objects
    // ============================================================================
    typedef std::vector< Chunk__ > Chunks__;
    Chunks__                       chunks__;

    // ============================================================================
    /// Last Chunk used for an allocation
    // ============================================================================
    Chunks__::iterator allocChunk__;

    // ============================================================================
    /// Last Chunk used for a deallocation
    // ============================================================================
    Chunks__::iterator deallocChunk__;
  };

}   // namespace gum

#ifndef GUM_NO_INLINE
#  include <agrum/tools/core/smallobjectallocator/fixedAllocator_inl.h>
#endif

#endif   // FIXEDALLOCATOR_H