Barrier.h

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/*
 * Copyright (C) 2007-2015 Hypertable, Inc.
 *
 * This file is part of Hypertable.
 *
 * Hypertable 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; version 3 of the
 * License, or any later version.
 *
 * Hypertable 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

#ifndef Common_Barrier_h
#define Common_Barrier_h

#include <condition_variable>
#include <mutex>

namespace Hypertable {

class Barrier {
  public:
    Barrier() { }

    void enter() {
      std::unique_lock<std::mutex> lock(m_mutex);
      m_unblocked_cond.wait(lock, [this](){ return !m_hold; });
      m_counter++;
    }

    void exit() {
      std::lock_guard<std::mutex> lock(m_mutex);
      HT_ASSERT(m_counter > 0);
      m_counter--;
      if (m_hold && m_counter == 0)
        m_quiesced_cond.notify_one();
    }

    void put_up() {
      std::unique_lock<std::mutex> lock(m_mutex);
      m_unblocked_cond.wait(lock, [this](){ return !m_hold; });
      m_hold = true;
      m_quiesced_cond.wait(lock, [this](){ return m_counter == 0; });
    }

    void take_down() {
      std::lock_guard<std::mutex> lock(m_mutex);
      m_hold = false;
      m_unblocked_cond.notify_all();
    }

    class ScopedActivator {
      public:
        ScopedActivator(Barrier &barrier) : m_barrier(barrier) {
          m_barrier.put_up();
        }

        ~ScopedActivator() {
          m_barrier.take_down();
        }

      private:
        Barrier &m_barrier;
    };

  private:
    std::mutex m_mutex;

    std::condition_variable m_unblocked_cond;

    std::condition_variable m_quiesced_cond;

    bool m_hold {};

    uint32_t m_counter {};
};

}

#endif // Common_Barrier_h