/* Copyright (C) 2014 InfiniDB, Inc.

   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; version 2 of
   the License.

   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., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

/*****************************************************************************
 * $Id$
 *
 ****************************************************************************/

/*
 * Brief description of the file contents
 *
 * More detailed description
 */

#include <iostream>
using namespace std;

#include <boost/thread.hpp>
#include <boost/thread/condition.hpp>
using namespace boost;

#define RWLOCK_LOCAL_DLLEXPORT
#include "rwlock_local.h"
#undef RWLOCK_LOCAL_DLLEXPORT

// semaphore numbers
#define MUTEX 0
#define READERS 1
#define WRITERS 2

#ifdef DEBUG
using namespace std;
#define PRINTSTATE()                                            \
  cerr << "  reading = " << state.reading << endl               \
       << "  writing = " << state.writing << endl               \
       << "  readerswaiting = " << state.readerswaiting << endl \
       << "  writerswaiting = " << state.writerswaiting << endl;

#define CHECKSAFETY()                                                               \
  if (!((state.reading == 0 && (state.writing == 0 || state.writing == 1)) ||       \
        (state.reading > 0 && state.writing == 0)))                                 \
  {                                                                                 \
    cerr << "RWLock_local::" << __func__ << ": safety invariant violation" << endl; \
    PRINTSTATE();                                                                   \
    throw std::logic_error("RWLock_local: safety invariant violation");             \
  }

#define CHECKLIVENESS()                                                               \
  if (!((!(state.readerswaiting > 0 || state.writerswaiting > 0) ||                   \
         (state.reading > 0 || state.writing > 0)) ||                                 \
        (!(state.reading == 0 && state.writing == 0) ||                               \
         (state.readerswaiting == 0 && state.writerswaiting == 0))))                  \
  {                                                                                   \
    cerr << "RWLock_local::" << __func__ << ": liveness invariant violation" << endl; \
    PRINTSTATE();                                                                     \
    throw std::logic_error("RWLock_local: liveness invariant violation");             \
  }

#undef CHECKLIVENESS
#define CHECKLIVENESS()

#endif

namespace rwlock
{
RWLock_local::RWLock_local()
{
  state.reading = 0;
  state.readerswaiting = 0;
  state.writing = 0;
  state.writerswaiting = 0;
}

RWLock_local::~RWLock_local()
{
}

void RWLock_local::read_lock()
{
  mutex.lock();
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  if (state.writerswaiting > 0 || state.writing > 0)
  {
    state.readerswaiting++;
#ifdef DEBUG
    CHECKSAFETY();
    CHECKLIVENESS();
#endif

    while (state.writerswaiting > 0 || state.writing > 0)
      okToRead.wait(mutex);

    state.readerswaiting--;
  }

  state.reading++;

#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  mutex.unlock();
}

void RWLock_local::read_unlock()
{
  mutex.lock();
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  state.reading--;

  if (state.writerswaiting > 0 && state.reading == 0)
    okToWrite.notify_one();

#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif
  mutex.unlock();
}

void RWLock_local::write_lock()
{
  mutex.lock();
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  if (state.writing > 0 || state.reading > 0)
  {
    state.writerswaiting++;

#ifdef DEBUG
    CHECKSAFETY();
    CHECKLIVENESS();
#endif

    while (state.writing > 0 || state.reading > 0)
      okToWrite.wait(mutex);

    state.writerswaiting--;
  }

  state.writing++;

#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif
}

void RWLock_local::write_unlock()
{
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  state.writing--;

  if (state.writerswaiting > 0)
    okToWrite.notify_one();
  else if (state.readerswaiting > 0)
    okToRead.notify_all();

#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif
  mutex.unlock();
}

void RWLock_local::upgrade_to_write()
{
  mutex.lock();
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif
  state.reading--;

  // try to cut in line
  if (state.reading == 0)
  {
    state.writing++;
#ifdef DEBUG
    CHECKSAFETY();
    CHECKLIVENESS();
#endif
    return;
  }

  // cut & paste from write_lock()
  if (state.writing > 0 || state.reading > 0)
  {
    state.writerswaiting++;

#ifdef DEBUG
    CHECKSAFETY();
    CHECKLIVENESS();
#endif

    while (state.writing > 0 || state.reading > 0)
      okToWrite.wait(mutex);

    state.writerswaiting--;
  }

  state.writing++;
}

/* It's safe (and necessary) to simply convert this writer to a reader without
 blocking */
void RWLock_local::downgrade_to_read()
{
#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif

  state.writing--;

  if (state.readerswaiting > 0)
    okToRead.notify_all();

  state.reading++;

#ifdef DEBUG
  CHECKSAFETY();
  CHECKLIVENESS();
#endif
  mutex.unlock();
}

void RWLock_local::lock()
{
  mutex.lock();
}

void RWLock_local::unlock()
{
  mutex.unlock();
}

int RWLock_local::getWriting()
{
  return state.writing;
}

int RWLock_local::getReading()
{
  return state.reading;
}

int RWLock_local::getWritersWaiting()
{
  return state.writerswaiting;
}

int RWLock_local::getReadersWaiting()
{
  return state.readerswaiting;
}

ScopedRWLock_local::ScopedRWLock_local(RWLock_local* l, rwlock_mode m)
{
  thelock = l;
  mode = m;
  assert(m == R || m == W);
  locked = false;
  lock();
}

ScopedRWLock_local::~ScopedRWLock_local()
{
  if (locked)
    unlock();
}

void ScopedRWLock_local::lock()
{
  if (mode == R)
    thelock->read_lock();
  else
    thelock->write_lock();

  locked = true;
}

void ScopedRWLock_local::unlock()
{
  if (mode == R)
    thelock->read_unlock();
  else
    thelock->write_unlock();

  locked = false;
}

}  // namespace rwlock