threadExecutorOMP_tpl.h

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/****************************************************************************
 *   This file is part of the aGrUM/pyAgrum library.                        *
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 *   Copyright (c) 2005-2026 by                                             *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
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 *   SPDX-FileCopyrightText: Copyright 2005-2026                            *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
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#pragma once
 

#include <agrum/base/core/threads/threadExecutorOMP.h>
 
 
#ifndef DOXYGEN_SHOULD_SKIP_THIS
 
 
namespace gum {
 
  namespace threadsOMP {

    template < typename FUNCTION, typename... ARGS >
    void ThreadExecutor::execute(std::size_t nb_threads, FUNCTION exec_func, ARGS&&... func_args) {
#  ifndef _OPENMP
      // without openMP we only have one thread available
      exec_func(0, 1, std::forward< ARGS >(func_args)...);
#  else
      if (nb_threads <= 1) {
        exec_func(0, 1, std::forward< ARGS >(func_args)...);
      } else {
        // allocate before incrementing so a bad_alloc leaves the counter unchanged
        std::vector< std::exception_ptr > func_exceptions(nb_threads, nullptr);
 
        // indicate that we start a new threadExecutor
        ++nbRunningThreadsExecutors_;
 
        // launch the threads and wait for their completion
#    pragma omp parallel num_threads(int(nb_threads))
        {
          // get the number of the thread
          const std::size_t this_thread = omp_get_thread_num();
 
          try {
            exec_func(this_thread, nb_threads, func_args...);
          } catch (...) { func_exceptions[this_thread] = std::current_exception(); }
        }
 
        // now, we have completed the execution of the ThreadExecutor
        --nbRunningThreadsExecutors_;
 
        // now, check if one exception has been raised
        for (const auto& exc: func_exceptions) {
          if (exc != nullptr) { std::rethrow_exception(exc); }
        }
      }
#  endif   // _OPENMP
    }

    template < typename FUNC1, typename FUNC2, typename... ARGS >
    void ThreadExecutor::executeOrUndo(std::size_t nb_threads,
                                       FUNC1       exec_func,
                                       FUNC2       undo_func,
                                       ARGS&&... func_args) {
#  ifndef _OPENMP
      // without openMP we only have one thread available
      try {
        exec_func(0, 1, std::forward< ARGS >(func_args)...);
      } catch (...) {
        undo_func(0, 1, std::forward< ARGS >(func_args)...);
        throw;
      }
#  else
      if (nb_threads <= 1) {
        try {
          exec_func(0, 1, std::forward< ARGS >(func_args)...);
        } catch (...) {
          undo_func(0, 1, std::forward< ARGS >(func_args)...);
          throw;
        }
      } else {
        // indicate that we start a new threadExecutor
        ++nbRunningThreadsExecutors_;
 
        // here, we shall create one std::exception_ptr for each thread openMP
        // that will be created. This will allow us to catch the exception raised
        // by the threads
        std::vector< std::exception_ptr > func_exceptions(nb_threads, nullptr);
 
        // launch the threads and waith for their completion
#    pragma omp parallel num_threads(int(nb_threads))
        {
          // get the number of the thread
          const std::size_t this_thread = getThreadNumber();
 
          try {
            exec_func(this_thread, nb_threads, func_args...);
          } catch (...) { func_exceptions[this_thread] = std::current_exception(); }
        }
 
        // now, check if one exception has been raised
        bool exception_raised = false;
        for (const auto& exc: func_exceptions) {
          if (exc != nullptr) {
            exception_raised = true;
            break;
          }
        }
 
        if (exception_raised) {
          // create the exceptions to catch during the repair threads executions
          std::vector< std::exception_ptr > undo_func_exceptions(nb_threads, nullptr);
 
          // launch the repair threads
#    pragma omp parallel num_threads(int(nb_threads))
          {
            // get the number of the thread
            const std::size_t this_thread = getThreadNumber();
 
            try {
              undo_func(this_thread, nb_threads, func_args...);
            } catch (...) { undo_func_exceptions[this_thread] = std::current_exception(); }
          }
 
          // now, we have completed the execution of the ThreadExecutor
          --nbRunningThreadsExecutors_;
 
          // rethrow the exception
          for (const auto& exc: func_exceptions) {
            if (exc != nullptr) { std::rethrow_exception(exc); }
          }
        } else {
          // now, we have completed the execution of the ThreadExecutor
          --nbRunningThreadsExecutors_;
        }
      }
#  endif   // _OPENMP
    }
 
  } /* namespace threadsOMP */
 
} /* namespace gum */
 
#endif /* DOXYGEN_SHOULD_SKIP_THIS */