parallel.h

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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2009 - 2024 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Part of the source code is dual licensed under Apache-2.0 WITH
// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
// governing the source code and code contributions can be found in
// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
//
// ------------------------------------------------------------------------
 
#ifndef dealii_parallel_h
#define dealii_parallel_h
 
 
#include <deal.II/base/config.h>
 
#include <deal.II/base/exceptions.h>
#include <deal.II/base/mutex.h>
#include <deal.II/base/synchronous_iterator.h>
#include <deal.II/base/template_constraints.h>
 
#include <cstddef>
#include <functional>
#include <memory>
#include <tuple>
 
#ifdef DEAL_II_WITH_TBB
#  include <tbb/blocked_range.h>
#  include <tbb/parallel_for.h>
#  include <tbb/parallel_reduce.h>
#  include <tbb/partitioner.h>
#else
#  include <boost/range/iterator_range.hpp>
#endif
 
#ifdef DEAL_II_HAVE_CXX20
#  include <concepts>
#endif
 
 
// TODO[WB]: allow calling functions to pass along a tbb::affinity_partitioner
// object to ensure that subsequent calls use the same cache lines
 
DEAL_II_NAMESPACE_OPEN
 
namespace parallel
{
  namespace internal
  {
    template <typename Number>
    struct EnableOpenMPSimdFor
    {
      static const bool value = true;
    };
 
#ifdef __INTEL_COMPILER
    // Disable long double SIMD instructions on ICC. This is to work around a
    // bug that generates wrong code at least up to intel 15 (see
    // tests/lac/vector-vector, tests/lac/intel-15-bug, and the discussion at
    // https://github.com/dealii/dealii/issues/598).
    template <>
    struct EnableOpenMPSimdFor<long double>
    {
      static const bool value = false;
    };
#endif
 
 
#ifdef DEAL_II_WITH_TBB
    template <typename Iterator, typename Functor>
    void
    parallel_for(Iterator           x_begin,
                 Iterator           x_end,
                 const Functor     &functor,
                 const unsigned int grainsize)
    {
      tbb::parallel_for(tbb::blocked_range<Iterator>(x_begin, x_end, grainsize),
                        functor,
                        tbb::auto_partitioner());
    }
 
 
 
    template <typename Iterator, typename Functor>
    void
    parallel_for(Iterator                                          x_begin,
                 Iterator                                          x_end,
                 const Functor                                    &functor,
                 const unsigned int                                grainsize,
                 const std::shared_ptr<tbb::affinity_partitioner> &partitioner)
    {
      tbb::parallel_for(tbb::blocked_range<Iterator>(x_begin, x_end, grainsize),
                        functor,
                        *partitioner);
    }
 
#else
 
    template <typename Iterator, typename Functor>
    void
    parallel_for(Iterator       x_begin,
                 Iterator       x_end,
                 const Functor &functor,
                 const unsigned int)
    {
      functor(boost::iterator_range<Iterator>(x_begin, x_end));
    }
 
#endif
  } // namespace internal
 
  template <typename InputIterator, typename OutputIterator, typename Function>
  DEAL_II_CXX20_REQUIRES(
    (std::invocable<Function, decltype(*std::declval<InputIterator>())> &&
     std::assignable_from<
       decltype(*std::declval<OutputIterator>()),
       std::invoke_result_t<Function,
                            decltype(*std::declval<InputIterator>())>>))
  void transform(const InputIterator &begin_in,
                 const InputIterator &end_in,
                 OutputIterator       out,
                 const Function      &function,
                 const unsigned int   grainsize)
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)grainsize;
 
    for (OutputIterator in = begin_in; in != end_in;)
      *out++ = function(*in++);
#else
    using Iterators     = std::tuple<InputIterator, OutputIterator>;
    using SyncIterators = SynchronousIterators<Iterators>;
    Iterators x_begin(begin_in, out);
    Iterators x_end(end_in, OutputIterator());
    internal::parallel_for(
      SyncIterators(x_begin),
      SyncIterators(x_end),
      [function](const auto &range) {
        for (const auto &p : range)
          *std::get<1>(p) = function(*std::get<0>(p));
      },
      grainsize);
#endif
  }
 
 
 
  template <typename InputIterator1,
            typename InputIterator2,
            typename OutputIterator,
            typename Function>
  DEAL_II_CXX20_REQUIRES(
    (std::invocable<Function,
                    decltype(*std::declval<InputIterator1>()),
                    decltype(*std::declval<InputIterator2>())> &&
     std::assignable_from<
       decltype(*std::declval<OutputIterator>()),
       std::invoke_result_t<Function,
                            decltype(*std::declval<InputIterator1>()),
                            decltype(*std::declval<InputIterator2>())>>))
  void transform(const InputIterator1 &begin_in1,
                 const InputIterator1 &end_in1,
                 InputIterator2        in2,
                 OutputIterator        out,
                 const Function       &function,
                 const unsigned int    grainsize)
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)grainsize;
 
    for (OutputIterator in1 = begin_in1; in1 != end_in1;)
      *out++ = function(*in1++, *in2++);
#else
    using Iterators =
      std::tuple<InputIterator1, InputIterator2, OutputIterator>;
    using SyncIterators = SynchronousIterators<Iterators>;
    Iterators x_begin(begin_in1, in2, out);
    Iterators x_end(end_in1, InputIterator2(), OutputIterator());
    internal::parallel_for(
      SyncIterators(x_begin),
      SyncIterators(x_end),
      [function](const auto &range) {
        for (const auto &p : range)
          *std::get<2>(p) = function(*std::get<0>(p), *std::get<1>(p));
      },
      grainsize);
#endif
  }
 
 
 
  template <typename InputIterator1,
            typename InputIterator2,
            typename InputIterator3,
            typename OutputIterator,
            typename Function>
  DEAL_II_CXX20_REQUIRES(
    (std::invocable<Function,
                    decltype(*std::declval<InputIterator1>()),
                    decltype(*std::declval<InputIterator2>()),
                    decltype(*std::declval<InputIterator3>())> &&
     std::assignable_from<
       decltype(*std::declval<OutputIterator>()),
       std::invoke_result_t<Function,
                            decltype(*std::declval<InputIterator1>()),
                            decltype(*std::declval<InputIterator2>()),
                            decltype(*std::declval<InputIterator3>())>>))
  void transform(const InputIterator1 &begin_in1,
                 const InputIterator1 &end_in1,
                 InputIterator2        in2,
                 InputIterator3        in3,
                 OutputIterator        out,
                 const Function       &function,
                 const unsigned int    grainsize)
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)grainsize;
 
    for (OutputIterator in1 = begin_in1; in1 != end_in1;)
      *out++ = function(*in1++, *in2++, *in3++);
#else
    using Iterators = std::
      tuple<InputIterator1, InputIterator2, InputIterator3, OutputIterator>;
    using SyncIterators = SynchronousIterators<Iterators>;
    Iterators x_begin(begin_in1, in2, in3, out);
    Iterators x_end(end_in1,
                    InputIterator2(),
                    InputIterator3(),
                    OutputIterator());
    internal::parallel_for(
      SyncIterators(x_begin),
      SyncIterators(x_end),
      [function](const auto &range) {
        for (const auto &p : range)
          *std::get<3>(p) =
            function(*std::get<0>(p), *std::get<1>(p), *std::get<2>(p));
      },
      grainsize);
#endif
  }
 
 
  namespace internal
  {
#ifdef DEAL_II_WITH_TBB
    template <typename Iterator, typename Function>
    DEAL_II_CXX20_REQUIRES((std::invocable<Function, Iterator, Iterator>))
    void apply_to_subranges(const tbb::blocked_range<Iterator> &range,
                            const Function                     &f)
    {
      f(range.begin(), range.end());
    }
#endif
  } // namespace internal
 
 
  template <typename Iterator, typename Function>
  DEAL_II_CXX20_REQUIRES((std::invocable<Function, Iterator, Iterator>))
  void apply_to_subranges(const Iterator                             &begin,
                          const std_cxx20::type_identity_t<Iterator> &end,
                          const Function                             &f,
                          const unsigned int                          grainsize)
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)grainsize;
 
    f(begin, end);
#else
    internal::parallel_for(
      begin,
      end,
      [&f](const tbb::blocked_range<Iterator> &range) {
        internal::apply_to_subranges<Iterator, Function>(range, f);
      },
      grainsize);
#endif
  }
 
 
 
  struct ParallelForInteger
  {
    virtual ~ParallelForInteger() = default;
 
    void
    apply_parallel(const std::size_t begin,
                   const std::size_t end,
                   const std::size_t minimum_parallel_grain_size) const;
 
    virtual void
    apply_to_subrange(const std::size_t, const std::size_t) const = 0;
  };
 
 
 
  template <typename ResultType, typename Iterator, typename Function>
  DEAL_II_CXX20_REQUIRES(
    (std::invocable<Function, Iterator, Iterator> &&
     std::convertible_to<std::invoke_result_t<Function, Iterator, Iterator>,
                         ResultType>))
  ResultType
    accumulate_from_subranges(const Function                             &f,
                              const Iterator                             &begin,
                              const std_cxx20::type_identity_t<Iterator> &end,
                              const unsigned int grainsize)
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)grainsize;
 
    return f(begin, end);
#else
    return tbb::parallel_reduce(
      tbb::blocked_range<Iterator>(begin, end, grainsize),
      ResultType(0),
      [f](const auto &range, const ResultType &starting_value) {
        ResultType value = starting_value;
        value += f(range.begin(), range.end());
        return value;
      },
      std::plus<ResultType>(),
      tbb::auto_partitioner());
#endif
  }
 
 
  // --------------------- for loop affinity partitioner -----------------------
 
  namespace internal
  {
    class TBBPartitioner
    {
    public:
      TBBPartitioner();
 
#ifdef DEAL_II_WITH_TBB
      ~TBBPartitioner();
 
      std::shared_ptr<tbb::affinity_partitioner>
      acquire_one_partitioner();
 
      void
      release_one_partitioner(
        const std::shared_ptr<tbb::affinity_partitioner> &p);
 
    private:
      std::shared_ptr<tbb::affinity_partitioner> my_partitioner;
 
      bool in_use;
 
      Threads::Mutex mutex;
#endif
    };
  } // namespace internal
} // namespace parallel
 
 
namespace internal
{
  namespace VectorImplementation
  {
    extern unsigned int minimum_parallel_grain_size;
  } // namespace VectorImplementation
 
 
  namespace SparseMatrixImplementation
  {
    extern unsigned int minimum_parallel_grain_size;
  } // namespace SparseMatrixImplementation
 
} // end of namespace internal
 
 
/* --------------------------- inline functions ------------------------- */
 
namespace parallel
{
  inline void
  ParallelForInteger::apply_parallel(
    const std::size_t begin,
    const std::size_t end,
    const std::size_t minimum_parallel_grain_size) const
  {
#ifndef DEAL_II_WITH_TBB
    // make sure we don't get compiler
    // warnings about unused arguments
    (void)minimum_parallel_grain_size;
 
    apply_to_subrange(begin, end);
#else
    internal::parallel_for(
      begin,
      end,
      [this](const tbb::blocked_range<std::size_t> &range) {
        apply_to_subrange(range.begin(), range.end());
      },
      minimum_parallel_grain_size);
#endif
  }
 
} // end of namespace parallel
 
DEAL_II_NAMESPACE_CLOSE
 
#endif