dumb_spinlock.hpp

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/*
 * Copyright (c) 2014-2015, Hewlett-Packard Development Company, LP.
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * HP designates this particular file as subject to the "Classpath" exception
 * as provided by HP in the LICENSE.txt file that accompanied this code.
 */
#ifndef FOEDUS_ASSORTED_DUMB_SPINLOCK_HPP_
#define FOEDUS_ASSORTED_DUMB_SPINLOCK_HPP_

#include "foedus/assert_nd.hpp"
#include "foedus/assorted/assorted_func.hpp"
#include "foedus/assorted/atomic_fences.hpp"
#include "foedus/assorted/raw_atomics.hpp"

namespace foedus {
namespace assorted {

class DumbSpinlock {
 public:
  DumbSpinlock(bool* locked, bool lock_initially = true) : locked_by_me_(false), locked_(locked) {
    if (lock_initially) {
      lock();
    }
  }
  ~DumbSpinlock() { unlock(); }

  bool is_locked_by_me() const { return locked_by_me_; }

  void lock() {
    SPINLOCK_WHILE(true) {
      if (try_lock()) {
        break;
      }
    }
  }
  bool try_lock() {
    if (locked_by_me_) {
      return true;  // already locked
    }

    bool expected = false;
    if (raw_atomic_compare_exchange_weak<bool>(locked_, &expected, true)) {
      ASSERT_ND(*locked_);
      locked_by_me_ = true;
      return true;
    } else {
      ASSERT_ND(expected);
      return false;
    }
  }

  void unlock() {
    if (locked_by_me_) {
      ASSERT_ND(*locked_);
      locked_by_me_ = false;
      assorted::memory_fence_acq_rel();
      *locked_ = false;
      assorted::memory_fence_acq_rel();
    }
  }

 private:
  bool        locked_by_me_;
  bool* const locked_;
};

}  // namespace assorted
}  // namespace foedus

#endif  // FOEDUS_ASSORTED_DUMB_SPINLOCK_HPP_