databaseTable_tpl.h

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/****************************************************************************
 *   This file is part of the aGrUM/pyAgrum library.                        *
 *                                                                          *
 *   Copyright (c) 2005-2026 by                                             *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
 *                                                                          *
 *   The aGrUM/pyAgrum library is free software; you can redistribute it    *
 *   and/or modify it under the terms of either :                           *
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 *    - 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,                              *
 *    - the MIT license (MIT),                                              *
 *    - or both in dual license, as here.                                   *
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 *   (see https://agrum.gitlab.io/articles/dual-licenses-lgplv3mit.html)    *
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 *   SPDX-FileCopyrightText: Copyright 2005-2026                            *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
 *   SPDX-License-Identifier: LGPL-3.0-or-later OR MIT                      *
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 *   Contact  : info_at_agrum_dot_org                                       *
 *   homepage : http://agrum.gitlab.io                                      *
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 ****************************************************************************/
 
#pragma once
 

#include <agrum/base/database/databaseTable.h>
 
#ifndef DOXYGEN_SHOULD_SKIP_THIS
 
namespace gum {
 
  namespace learning {
 
    // a method to process the rows of the database in multithreading
    template < typename Functor1, typename Functor2 >
    void DatabaseTable::_threadProcessDatabase_(Functor1& exec_func, Functor2& undo_func) {
      // compute the number of threads to execute the code
      const std::size_t nb_threads = this->nbProcessingThreads_();
 
      // if there is just one thread, let it process all the rows
      if (nb_threads == 1) {
        const std::size_t db_size = this->nbRows();
        exec_func(std::size_t(0), db_size, 0);
        return;
      }
 
      // if there are multiple threads, compute the ranges of rows they should process
      const std::vector< std::pair< std::size_t, std::size_t > > ranges
          = this->rangesProcessingThreads_(nb_threads);
 
      // here, we shall create the threads, but also one std::exception_ptr
      // for each thread. This will allow us to catch the exception raised
      // by the threads
      std::vector< std::thread > threads;
      threads.reserve(nb_threads);
      std::vector< std::exception_ptr > func_exceptions(nb_threads, nullptr);
 
      // create a lambda that will execute exec_func while catching its exceptions
      auto real_exec_func = [&exec_func](std::size_t         begin,
                                         std::size_t         end,
                                         std::size_t         index,
                                         std::exception_ptr& exc) -> void {
        try {
          exec_func(begin, end, index);
        } catch (...) { exc = std::current_exception(); }
      };
 
      // launch the threads
      for (std::size_t i = std::size_t(0); i < nb_threads; ++i) {
        threads.push_back(std::thread(std::ref(real_exec_func),
                                      ranges[i].first,
                                      ranges[i].second,
                                      i,
                                      std::ref(func_exceptions[i])));
      }
 
      // wait for the threads to complete their executions
      std::for_each(threads.begin(), threads.end(), std::mem_fn(&std::thread::join));
 
      // 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 a lambda that will execute undo_func while catching
        // its exceptions
        auto real_undo_func = [&undo_func](std::size_t         begin,
                                           std::size_t         end,
                                           std::size_t         index,
                                           std::exception_ptr& exc) -> void {
          try {
            undo_func(begin, end, index);
          } catch (...) { exc = std::current_exception(); }
        };
 
        // launch the repair threads
        threads.clear();
        std::vector< std::exception_ptr > undo_func_exceptions(nb_threads, nullptr);
        for (std::size_t i = std::size_t(0); i < nb_threads; ++i) {
          // we just need to repair the threads that did not raise exceptions
          if (func_exceptions[i] == nullptr)
            threads.push_back(std::thread(std::ref(real_undo_func),
                                          ranges[i].first,
                                          ranges[i].second,
                                          i,
                                          std::ref(undo_func_exceptions[i])));
        }
 
        // wait for the threads to complete their executions
        std::for_each(threads.begin(), threads.end(), std::mem_fn(&std::thread::join));
 
        // rethrow the exception
        for (const auto& exc: func_exceptions) {
          if (exc != nullptr) { std::rethrow_exception(exc); }
        }
      }
    }
 
  } /* namespace learning */
 
} /* namespace gum */
 
#endif /* DOXYGEN_SHOULD_SKIP_THIS */