// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
// vi: set et ts=4 sw=4 sts=4:
/*
  This file is part of the Open Porous Media project (OPM).

  OPM is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 2 of the License, or
  (at your option) any later version.

  OPM is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with OPM.  If not, see <http://www.gnu.org/licenses/>.

  Consult the COPYING file in the top-level source directory of this
  module for the precise wording of the license and the list of
  copyright holders.
*/
/*!
 * \file
 * \copydoc Opm::ThreadManager
 */
#ifndef EWOMS_THREAD_MANAGER_HH
#define EWOMS_THREAD_MANAGER_HH

#ifdef _OPENMP
#include <omp.h>
#endif

#include <opm/models/utils/parametersystem.hh>
#include <opm/models/utils/propertysystem.hh>

#include <dune/common/version.hh>

namespace Opm {

/*!
 * \brief Simplifies multi-threaded capabilities.
 */
template <class TypeTag>
class ThreadManager
{
public:
    enum {
#if defined(_OPENMP) || DOXYGEN
        //! Specify whether OpenMP is really available or not
        isFake = false
#else
        isFake = true
#endif
    };

    /*!
     * \brief Register all run-time parameters of the thread manager.
     */
    static void registerParameters()
    {
        EWOMS_REGISTER_PARAM(TypeTag, int, ThreadsPerProcess,
                             "The maximum number of threads to be instantiated per process "
                             "('-1' means 'automatic')");
    }

    /*!
     * \brief Initialize number of threads used thread manager.
     *
     * \param queryCommandLineParameter if set to true we will query ThreadsPerProcess
     *        and if set (disregard the environment variable OPM_NUM_THREADS).
     *        If false we will assume that the number of OpenMP threads is already set
     *        outside of this function (e.g. by OPM_NUM_THREADS or in the simulator by
     *        the ThreadsPerProcess parameter).
     */
    static void init(bool queryCommandLineParameter = true)
    {
        if (queryCommandLineParameter)
        {
            numThreads_ = EWOMS_GET_PARAM(TypeTag, int, ThreadsPerProcess);

            // some safety checks. This is pretty ugly macro-magic, but so what?
#if !defined(_OPENMP)
            if (numThreads_ != 1 && numThreads_ != -1)
                throw std::invalid_argument("OpenMP is not available. The only valid values for "
                                            "threads-per-process is 1 and -1 but it is "+std::to_string(numThreads_)+"!");
            numThreads_ = 1;
#elif !defined NDEBUG && defined DUNE_INTERFACECHECK
            if (numThreads_ != 1)
                throw std::invalid_argument("You explicitly enabled Barton-Nackman interface checking in Dune. "
                                            "The Dune implementation of this is currently incompatible with "
                                            "thread parallelism!");
            numThreads_ = 1;
#else

            if (numThreads_ == 0)
                throw std::invalid_argument("Zero threads per process are not possible: It must be at least 1, "
                                            "(or -1 for 'automatic')!");
#endif

#ifdef _OPENMP
            // actually limit the number of threads
            if (numThreads_ > 0)
                omp_set_num_threads(numThreads_);
#endif
        }

#ifdef _OPENMP
        // get the number of threads which are used in the end.
        numThreads_ = omp_get_max_threads();
#endif
    }

    /*!
     * \brief Return the maximum number of threads of the current process.
     */
    static unsigned maxThreads()
    { return static_cast<unsigned>(numThreads_); }

    /*!
     * \brief Return the index of the current OpenMP thread
     */
    static unsigned threadId()
    {
#ifdef _OPENMP
        return static_cast<unsigned>(omp_get_thread_num());
#else
        return 0;
#endif
    }

private:
    static int numThreads_;
};

template <class TypeTag>
int ThreadManager<TypeTag>::numThreads_ = 1;
} // namespace Opm

#endif
