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/* Copyright (C) 2011 Free Software Foundation, Inc.
   Contributed by Torvald Riegel <triegel@redhat.com>.
 
   This file is part of the GNU Transactional Memory Library (libitm).
 
   Libitm 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.
 
   Libitm 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.
 
   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.
 
   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */
 
#ifndef GTM_RWLOCK_H
#define GTM_RWLOCK_H
 
#include "local_atomic"
#include "common.h"
 
namespace GTM HIDDEN {
 
struct gtm_thread;
 
// This datastructure is the blocking, futex-based version of the Dekker-style
// reader-writer lock used to provide mutual exclusion between active and
// serial transactions.
// See libitm's documentation for further details.
//
// In this implementation, writers are given highest priority access but
// read-to-write upgrades do not have a higher priority than writers.
 
class gtm_rwlock
{
  // TODO Put futexes on different cachelines?
  std::atomic<int> writers;       // Writers' futex.
  std::atomic<int> writer_readers;// A confirmed writer waits here for readers.
  std::atomic<int> readers;       // Readers wait here for writers (iff true).
 
 public:
  gtm_rwlock() : writers(0), writer_readers(0), readers(0) {};
 
  void read_lock (gtm_thread *tx);
  void read_unlock (gtm_thread *tx);
 
  void write_lock ();
  void write_unlock ();
 
  bool write_upgrade (gtm_thread *tx);
  void write_upgrade_finish (gtm_thread *tx);
 
 protected:
  bool write_lock_generic (gtm_thread *tx);
};
 
} // namespace GTM
 
#endif // GTM_RWLOCK_H