ParallelExecutorOPENMP.hpp

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////////////////////////////////////////////////////////////////////////////////
// This file is distributed under the University of Illinois/NCSA Open Source
// License.  See LICENSE file in top directory for details.
//
// Copyright (c) 2020 QMCPACK developers.
//
// File developed by: Peter Doak, doakpw@ornl.gov, Oak Ridge National Lab
//                    Ye Luo, yeluo@anl.gov, Argonne National Laboratory
//
// File created by: Peter Doak, doakpw@ornl.gov, Oak Ridge National Lab
////////////////////////////////////////////////////////////////////////////////


/** @file
 *  @brief implementation of openmp specialization of ParallelExecutor
 */
#ifndef QMCPLUSPLUS_PARALLELEXECUTOR_OPENMP_HPP
#define QMCPLUSPLUS_PARALLELEXECUTOR_OPENMP_HPP

#include <stdexcept>
#include <string>
#include <iostream>

#include "Concurrency/ParallelExecutor.hpp"
#include "Concurrency/OpenMP.h"

namespace qmcplusplus
{
/** implements parallel tasks executed by threads in an OpenMP thread pool.
 *
 *  This specialization throws below the top openmp theading level
 *  exception must be caught at thread level or terminate is called.
 *
 */
template<>
template<typename F, typename... Args>
void ParallelExecutor<Executor::OPENMP>::operator()(int num_tasks, F&& f, Args&&... args)
{
  const std::string nesting_error{"ParallelExecutor should not be used for nested openmp threading\n"};
  if (omp_get_level() > 0)
    throw std::runtime_error(nesting_error);
  int nested_throw_count = 0;
  int throw_count        = 0;
#pragma omp parallel for reduction(+ : nested_throw_count, throw_count)
  for (int task_id = 0; task_id < num_tasks; ++task_id)
  {
    try
    {
      f(task_id, std::forward<Args>(args)...);
    }
    catch (const std::runtime_error& re)
    {
      if (nesting_error == re.what())
        ++nested_throw_count;
      else
      {
        std::cerr << re.what() << std::flush;
        ++throw_count;
      }
    }
    catch (...)
    {
      ++throw_count;
    }
  }
  if (throw_count > 0)
    throw std::runtime_error("Unexpected exception thrown in threaded section");
  else if (nested_throw_count > 0)
    throw std::runtime_error(nesting_error);
}

} // namespace qmcplusplus

#endif