/******************************************************************************
 * src/tools/jobqueue.h
 *
 * Job queue class for work-balancing parallel string sorting algorithms.
 *
 ******************************************************************************
 * Copyright (C) 2013 Timo Bingmann <tb@panthema.net>
 *
 * This program 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 3 of the License, or (at your option)
 * any later version.
 *
 * This program 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
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 *****************************************************************************/

#include <iostream>
#include <assert.h>
#include <omp.h>

#include "src/config.h"

#if defined(HAVE_ATOMIC_H)
#include <atomic>
#elif defined(HAVE_CSTDATOMIC_H)
#include <cstdatomic>
#endif

#include <tbb/concurrent_queue.h>

#include "../tools/debug.h"

namespace jobqueue {

static const bool debug_queue = false;

// ****************************************************************************
// *** Job and JobQueue system with lock-free queue and OpenMP threads

class Job
{
public:
    virtual ~Job() {};

    /// virtual function that is called by the JobQueue
    virtual void run(class JobQueue& jobqueue) = 0;
};

class JobQueue
{
private:

    /// lock-free data structure containing pointers to Job objects.
    tbb::concurrent_queue<Job*>   m_queue;

    /// number of threads idle
    std::atomic<int>            m_idle_count;

public:

    JobQueue()
        : m_queue(),
          m_idle_count( 0 )
    {
    }

    bool has_idle() const
    {
        return (m_idle_count != 0);
    }

    void enqueue(class Job* job)
    {
        m_queue.push(job);
    }

    void loop()
    {
#pragma omp parallel
        {
            Job* job = NULL;

            while(1)
            {
                if (m_queue.try_pop(job))
                {
                RUNJOB:
                    job->run(*this);
                    delete job;
                }
                else
                {
                    DBG(debug_queue, "Queue is empty");
                    ++m_idle_count;

                    while (m_idle_count != omp_get_num_threads())
                    {
                        DBG(debug_queue, "Idle thread - m_idle_count: " << m_idle_count);
                        if (m_queue.try_pop(job))
                        {
                            --m_idle_count;
                            goto RUNJOB;
                        }
                    }

                    assert(m_idle_count == omp_get_num_threads());
                    break;
                }
            }
        } // end omp parallel
    }
};

} // namespace jobqueue