text: /*
   * This file is part of the GROMACS molecular simulation package.
   *
   * Copyright 2017- The GROMACS Authors
   * and the project initiators Erik Lindahl, Berk Hess and David van der Spoel.
   * Consult the AUTHORS/COPYING files and https://www.gromacs.org for details.
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  /*! \file
   * \brief Declares allocation policy classes and allocators that are
   * used to make library containers compatible with alignment
   * requirements of particular hardware, e.g. memory operations for
   * SIMD or accelerators.
   *
   * \author Erik Lindahl <erik.lindahl@gmail.com>
   * \author Mark Abraham <mark.j.abraham@gmail.com>
   * \inpublicapi
   * \ingroup module_utility
   */
  #ifndef GMX_UTILITY_ALIGNEDALLOCATOR_H
  #define GMX_UTILITY_ALIGNEDALLOCATOR_H
  
  #include <cstddef>
  
  #include "gromacs/utility/allocator.h"
  
  namespace gmx
  {
  
  /*! \libinternal \brief Policy class for configuring gmx::Allocator, to manage
   * allocations of aligned memory for SIMD code.
   */
  class AlignedAllocationPolicy
  {
  public:
      /*! \brief Return the alignment size. */
      static std::size_t alignment();
      /*! \brief Allocate memory aligned to alignment() bytes.
       *
       *  \param bytes Amount of memory (bytes) to allocate. It is valid to ask for
       *               0 bytes, which will return a non-null pointer that is properly
       *               aligned and padded (but that you should not use).
       *
       * \return Valid pointer if the allocation worked, otherwise nullptr.
       *
       * The memory will always be aligned to 128 bytes, which is our
       * estimate of the longest cache lines on architectures currently in use.
       * It will also be padded by the same amount at the end of the
       * area, to help avoid false cache sharing.
       *
       *  \note Memory allocated with this routine must be released with
       *        gmx::AlignedAllocationPolicy::free(), and absolutely not the system free().
       */
      static void* malloc(std::size_t bytes);
      /*! \brief Free aligned memory
       *
       *  \param p  Memory pointer previously returned from malloc()
       *
       *  \note This routine should only be called with pointers obtained from
       *        gmx::AlignedAllocationPolicy::malloc(), and absolutely not any
       *        pointers obtained the system malloc().
       */
      static void free(void* p);
  };
  
  /*! \brief Aligned memory allocator.
   *
   *  \tparam T          Type of objects to allocate
   *
   * This convenience partial specialization can be used for the
   * optional allocator template parameter in standard library
   * containers, which is necessary e.g. to use SIMD aligned load and
   * store operations on data in those containers. The memory will
   * always be aligned according to the behavior of
   * AlignedAllocationPolicy.
   */
  template<class T>
  using AlignedAllocator = Allocator<T, AlignedAllocationPolicy>;
  
  
  /*! \brief Return the memory page size on this system
   *
   * Implements the "construct on first use" idiom to avoid the static
   * initialization order fiasco where a possible static page-aligned
   * container would be initialized before the alignment variable was.
   *
   * Note that thread-safety is guaranteed by the C++11 language
   * standard. */
  std::size_t pageSize();
  
  /*! \libinternal \brief Policy class for configuring gmx::Allocator,
   * to manage allocations of page-aligned memory that can be locked for
   * asynchronous transfer to GPU devices.
   */
  class PageAlignedAllocationPolicy
  {
  public:
      /*! \brief Return the alignment size of memory pages on this system.
       *
       * Queries sysconf/WinAPI, otherwise guesses 4096. */
      static std::size_t alignment();
      /*! \brief Allocate memory aligned to alignment() bytes.
       *
       *  \param bytes Amount of memory (bytes) to allocate. It is valid to ask for
       *               0 bytes, which will return a non-null pointer that is properly
       *               aligned and padded (but that you should not use).
       *
       * \return Valid pointer if the allocation worked, otherwise nullptr.
       *
       *  \note Memory allocated with this routine must be released with
       *        gmx::PageAlignedAllocationPolicy::free(), and absolutely not the system free().
       */
      static void* malloc(std::size_t bytes);
      /*! \brief Free aligned memory
       *
       *  \param p  Memory pointer previously returned from malloc()
       *
       *  \note This routine should only be called with pointers obtained from
       *        gmx::PageAlignedAllocationPolicy::malloc(), and absolutely not any
       *        pointers obtained the system malloc().
       */
      static void free(void* p);
  };
  
  /*! \brief PageAligned memory allocator.
   *
   *  \tparam T          Type of objects to allocate
   *
   * This convenience partial specialization can be used for the
   * optional allocator template parameter in standard library
   * containers, which is necessary for locking memory pages for
   * asynchronous transfer between a GPU device and the host.  The
   * memory will always be aligned according to the behavior of
   * PageAlignedAllocationPolicy.
   */
  template<class T>
  using PageAlignedAllocator = Allocator<T, PageAlignedAllocationPolicy>;
  
  } // namespace gmx
  
  #endif // GMX_UTILITY_ALIGNEDALLOCATOR_H
  