OCCT

// Created on: 2005-03-15
// Created by: Peter KURNEV
// Copyright (c) 2005-2014 OPEN CASCADE SAS
//
// This file is part of Open CASCADE Technology software library.
//
// This library is free software; you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License version 2.1 as published
// by the Free Software Foundation, with special exception defined in the file
// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
// distribution for complete text of the license and disclaimer of any warranty.
//
// Alternatively, this file may be used under the terms of Open CASCADE
// commercial license or contractual agreement.

#ifndef _Standard_MMgrOpt_HeaderFile
#define _Standard_MMgrOpt_HeaderFile

#include <Standard_MMgrRoot.hxx>

#include <mutex>

/**
 * @brief Open CASCADE memory manager optimized for speed.
 *
 * The behaviour is different for memory blocks of different sizes,
 * according to specified options provided to constructor:
 *
 * - Small blocks with size less than or equal to aCellSize are allocated
 *   in big pools of memory. The parameter aNbPages specifies size of
 *   these pools in pages (operating system-dependent).
 *   When freed, small block is not returned to the system but added
 *   into free blocks list and reused when block of the same size is
 *   requested.
 *
 * - Medium size blocks with size less than aThreshold are allocated
 *   using malloc() or calloc() function but not returned to the system
 *   when method Free() is called; instead they are put into free list
 *   and reused when block of the same size is requested.
 *   Blocks of medium size stored in free lists can be released to the
 *   system (by free()) by calling method Purge().
 *
 * - Large blocks with size greater than or equal to aThreshold are allocated
 *   and freed directly: either using malloc()/calloc() and free(), or using
 *   memory mapped files (if option aMMap is True)
 *
 * Thus the optimization of memory allocation/deallocation is reached
 * for small and medium size blocks using free lists method;
 * note that space allocated for small blocks cannot be (currently) released
 * to the system while space for medium size blocks can be released by method Purge().
 *
 * Note that destructor of that class frees all free lists and memory pools
 * allocated for small blocks.
 *
 * Note that size of memory blocks allocated by this memory manager is always
 * rounded up to 16 bytes. In addition, 8 bytes are added at the beginning
 * of the memory block to hold auxiliary information (size of the block when
 * in use, or pointer to the next free block when in free list).
 * This the expense of speed optimization. At the same time, allocating small
 * blocks is usually less costly than directly by malloc since allocation is made
 * once (when allocating a pool) and overheads induced by malloc are minimized.
 */
class Standard_MMgrOpt : public Standard_MMgrRoot
{
public:
  //! Constructor. If aClear is True, the allocated emmory will be
  //! nullified. For description of other parameters, see description
  //! of the class above.
  Standard_EXPORT Standard_MMgrOpt(const bool   aClear     = true,
                                   const bool   aMMap      = true,
                                   const size_t aCellSize  = 200,
                                   const int    aNbPages   = 10000,
                                   const size_t aThreshold = 40000);

  //! Frees all free lists and pools allocated for small blocks
  Standard_EXPORT ~Standard_MMgrOpt() override;

  //! Allocate aSize bytes; see class description above
  Standard_EXPORT void* Allocate(const size_t aSize) override;

  //! Reallocate previously allocated aPtr to a new size; new address is returned.
  //! In case that aPtr is null, the function behaves exactly as Allocate.
  Standard_EXPORT void* Reallocate(void* thePtr, const size_t theSize) override;

  //! Free previously allocated block.
  //! Note that block can not all blocks are released to the OS by this
  //! method (see class description)
  Standard_EXPORT void Free(void* thePtr) override;

  //! Release medium-sized blocks of memory in free lists to the system.
  //! Returns number of actually freed blocks
  Standard_EXPORT int Purge(bool isDestroyed) override;

  //! Declaration of a type pointer to the callback function that should accept the following
  //! arguments:
  //! @param theIsAlloc   true if the data is allocated, false if it is freed
  //! @param theStorage   address of the allocated/freed block
  //! @param theRoundSize the real rounded size of the block
  //! @param theSize      the size of the block that was requested by application (this value is
  //! correct only if theIsAlloc is true)
  typedef void (*TPCallBackFunc)(const bool   theIsAlloc,
                                 void* const  theStorage,
                                 const size_t theRoundSize,
                                 const size_t theSize);

  //! Set the callback function. You may pass 0 there to turn off the callback.
  //! The callback function, if set, will be automatically called from within
  //! Allocate and Free methods.
  Standard_EXPORT static void SetCallBackFunction(TPCallBackFunc pFunc);

protected:
  //! Internal - initialization of buffers
  Standard_EXPORT void Initialize();

  //! Internal - allocation of memory using either malloc or memory mapped files.
  //! The size of the actually allocated block may be greater than requested one
  //! when memory mapping is used, since it is aligned to page size
  size_t* AllocMemory(size_t& aSize);

  //! Internal - deallocation of memory taken by AllocMemory
  void FreeMemory(void* aPtr, const size_t aSize);

  //! Internal - free memory pools allocated for small size blocks
  void FreePools();

protected:
  bool myClear; //!< option to clear allocated memory

  size_t   myFreeListMax; //!< last allocated index in the free blocks list
  size_t** myFreeList;    //!< free blocks list

  size_t  myCellSize;  //!< small blocks size
  int     myNbPages;   //!< size (pages) for small block memory pools
  size_t  myPageSize;  //!< system-dependent memory page size
  size_t* myAllocList; //!< list of memory pools for small blocks
  size_t* myNextAddr;  //!< next free address in the active memory pool
  size_t* myEndBlock;  //!< end of the active memory pool

  // clang-format off
  int myMMap;          //!< non-null if using memory mapped files for allocation of large blocks
  // clang-format on
  size_t myThreshold; //!< large block size

  std::mutex myMutex;      //!< Mutex to protect free lists data
  std::mutex myMutexPools; //!< Mutex to protect small block pools data
};

#endif