/* 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. */

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

#include <unistd.h>
#include <iostream>
#include <stdexcept>
#include <string>
#include <sstream>
#include <iomanip>
#include <tr1/unordered_map>

#ifndef NDEBUG
#define NDEBUG
#endif
#include <cassert>
using namespace std;

#include <boost/thread/thread.hpp>

#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/sync/named_semaphore.hpp>
#include <boost/version.hpp>
namespace bi = boost::interprocess;

#define RWLOCK_DLLEXPORT
#include "rwlock.h"
#undef RWLOCK_DLLEXPORT

using namespace boost::posix_time;

#include "shmkeys.h"

#include "installdir.h"

namespace
{
using namespace rwlock;

// This mutex needs to be fully instantiated by the runtime static object
// init mechanism or the lock in makeRWLockShmImpl() will fail
boost::mutex instanceMapMutex;
typedef std::tr1::unordered_map<int, RWLockShmImpl*> LockMap_t;
// Windows doesn't init static objects the same as Linux, so make this a ptr
LockMap_t* lockMapPtr = 0;

}  // namespace

namespace rwlock
{
#if defined(DEBUG) && !defined(_MSC_VER)
#define RWLOCK_DEBUG
#endif

#ifdef RWLOCK_DEBUG
#define PRINTSTATE()                                                      \
  cerr << "  reading = " << fPImpl->fState->reading << endl               \
       << "  writing = " << fPImpl->fState->writing << endl               \
       << "  readerswaiting = " << fPImpl->fState->readerswaiting << endl \
       << "  writerswaiting = " << fPImpl->fState->writerswaiting << endl

#define CHECKSAFETY()                                                                           \
  do                                                                                            \
  {                                                                                             \
    if (!((fPImpl->fState->reading == 0 &&                                                      \
           (fPImpl->fState->writing == 0 || fPImpl->fState->writing == 1)) ||                   \
          (fPImpl->fState->reading > 0 && fPImpl->fState->writing == 0)))                       \
    {                                                                                           \
      cerr << __PRETTY_FUNCTION__ << ":" << __LINE__ << ": safety invariant violation" << endl; \
      PRINTSTATE();                                                                             \
      throw std::logic_error("RWLock: safety invariant violation");                             \
    }                                                                                           \
  } while (0)

#define CHECKLIVENESS()                                                                           \
  do                                                                                              \
  {                                                                                               \
    if (!((!(fPImpl->fState->readerswaiting > 0 || fPImpl->fState->writerswaiting > 0) ||         \
           (fPImpl->fState->reading > 0 || fPImpl->fState->writing > 0)) ||                       \
          (!(fPImpl->fState->reading == 0 && fPImpl->fState->writing == 0) ||                     \
           (fPImpl->fState->readerswaiting == 0 && fPImpl->fState->writerswaiting == 0))))        \
    {                                                                                             \
      cerr << __PRETTY_FUNCTION__ << ":" << __LINE__ << ": liveness invariant violation" << endl; \
      PRINTSTATE();                                                                               \
      throw std::logic_error("RWLock: liveness invariant violation");                             \
    }                                                                                             \
  } while (0)
#else
#define PRINTSTATE() (void)0
#define CHECKSAFETY() (void)0
#define CHECKLIVENESS() (void)0
#endif

/*static*/
RWLockShmImpl* RWLockShmImpl::makeRWLockShmImpl(int key, bool* excl)
{
  boost::mutex::scoped_lock lk(instanceMapMutex);
  LockMap_t::iterator iter;

  if (!lockMapPtr)
    lockMapPtr = new LockMap_t();

  iter = lockMapPtr->find(key);

  if (iter == lockMapPtr->end())
  {
    RWLockShmImpl* ptr = 0;
    bool bExcl = excl ? *excl : false;
    ptr = new RWLockShmImpl(key, bExcl);
    lockMapPtr->insert(make_pair(key, ptr));
    return ptr;
  }
  else if (excl)
  {
    *excl = false;  // This isn't the first time for this lock.
  }

  return iter->second;
}

RWLockShmImpl::RWLockShmImpl(int key, bool excl)
{
  string keyName = BRM::ShmKeys::keyToName(key);
  fKeyString = keyName;

  try
  {
    bi::permissions perms;
    perms.set_unrestricted();
    bi::shared_memory_object shm(bi::create_only, keyName.c_str(), bi::read_write, perms);
    shm.truncate(sizeof(struct State));
    fStateShm.swap(shm);
    bi::mapped_region region(fStateShm, bi::read_write);
    fRegion.swap(region);
    fState = static_cast<State*>(fRegion.get_address());
    fState->writerswaiting = 0;
    fState->readerswaiting = 0;
    fState->reading = 0;

    if (excl)
      fState->writing = 1;
    else
      fState->writing = 0;

    new (&fState->sems[RWLock::MUTEX]) bi::interprocess_semaphore(1);
    new (&fState->sems[RWLock::READERS]) bi::interprocess_semaphore(0);
    new (&fState->sems[RWLock::WRITERS]) bi::interprocess_semaphore(0);
  }
  catch (bi::interprocess_exception& e)
  {
    if (e.get_error_code() == bi::security_error)
    {
      cerr << "RWLock:  Failed to create the lock.  Check perms on /dev/shm; should be 1777" << endl;
      throw;
    }
    if (e.get_error_code() == bi::already_exists_error && excl)
      throw not_excl();
    if (e.get_error_code() != bi::already_exists_error)
      throw;

    try
    {
      bi::shared_memory_object shm(bi::open_only, keyName.c_str(), bi::read_write);
      fStateShm.swap(shm);
    }
    catch (exception& e)
    {
      cerr << "RWLock failed to attach to the " << keyName << " shared mem segment, got " << e.what() << endl;
      throw;
    }
    bi::mapped_region region(fStateShm, bi::read_write);
    fRegion.swap(region);
    fState = static_cast<State*>(fRegion.get_address());
  }
  catch (...)
  {
    runtime_error rex("RWLockShmImpl::RWLockShmImpl(): caught unknown exception");
    cerr << rex.what() << endl;
    throw rex;
  }
}

RWLock::RWLock(int key, bool* excl)
{
  fPImpl = RWLockShmImpl::makeRWLockShmImpl(key, excl);
}

RWLock::~RWLock()
{
}

void RWLock::down(int num, bool block)
{
again:

  try
  {
    if (block)
      fPImpl->fState->sems[num].wait();
    else
    {
      bool gotIt = fPImpl->fState->sems[num].try_wait();

      if (!gotIt)
        throw wouldblock();
    }
  }
  catch (bi::interprocess_exception& bipe)
  {
    ostringstream os;
    os << "RWLock::down(): caught boost ipe: " << bipe.what() << " key = " << fPImpl->keyString()
       << " error code = " << bipe.get_error_code();

    if (bipe.get_error_code() == 1)  // it passes through EINTR apparently
      goto again;

    runtime_error rex(os.str());
    cerr << bipe.what() << endl;
    throw rex;
  }
  catch (std::exception& ex)
  {
    cerr <<
        __PRETTY_FUNCTION__ <<
        ":" << __LINE__ << ": caught an exception: " << ex.what() << endl;
    throw;
  }
  catch (...)
  {
    cerr <<
        __PRETTY_FUNCTION__ <<
        ":" << __LINE__ << ": caught an exception" << endl;
    throw runtime_error("RWLock::down(): caught an exception");
  }
}

bool RWLock::timed_down(int num, const ptime& delay)
{
  bool gotTheLock = false;

  //	cout << "timed_down: current time = " << to_simple_string(microsec_clock::local_time()) <<
  //			"  wake time = " << to_simple_string(delay) << endl;

again:

  try
  {
    // I don't think I've seen timed_wait() ever wait, need to do this 'manually'
    // gotTheLock = fPImpl->fState->sems[num].timed_wait(delay);
    do
    {
      gotTheLock = fPImpl->fState->sems[num].try_wait();

      if (!gotTheLock)
        usleep(100000);
    } while (!gotTheLock && microsec_clock::local_time() < delay);
  }
  catch (boost::thread_interrupted&)
  {
    // no need to do anything here
  }
  catch (bi::interprocess_exception& bipe)
  {
    ostringstream os;
    os << "RWLock::timed_down(): caught boost ipe: " << bipe.what() << " key = " << fPImpl->keyString()
       << " error code = " << bipe.get_error_code();

    if (bipe.get_error_code() == 1)  // it passes through EINTR apparently
      goto again;

    runtime_error rex(os.str());
    cerr << bipe.what() << endl;
    throw rex;
  }
  catch (std::exception& ex)
  {
    cerr <<
        __PRETTY_FUNCTION__ <<
        ":" << __LINE__ << ": caught an exception: " << ex.what() << endl;
    throw;
  }
  catch (...)
  {
    cerr <<
        __PRETTY_FUNCTION__ <<
        ":" << __LINE__ << ": caught an exception" << endl;
    throw runtime_error("RWLock::timed_down(): caught an exception");
  }

  return gotTheLock;
}

void RWLock::up(int num)
{
  try
  {
    fPImpl->fState->sems[num].post();
  }
  catch (bi::interprocess_exception& bipe)
  {
    ostringstream os;
    os << "RWLock::up(): caught boost ipe: " << bipe.what() << " key = " << fPImpl->keyString();
    runtime_error rex(os.str());
    cerr << bipe.what() << endl;
    throw rex;
  }
  catch (...)
  {
    throw runtime_error("RWLock::up(): caught an exception");
  }
}

void RWLock::read_lock(bool block)
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  if (fPImpl->fState->writerswaiting > 0 || fPImpl->fState->writing > 0)
  {
    if (!block)
    {
      up(MUTEX);
      throw wouldblock();
    }

    fPImpl->fState->readerswaiting++;
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    down(READERS);  // unblocked by write_unlock();
#ifdef RWLOCK_DEBUG
    down(MUTEX, true);
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
#endif
  }
  else
  {
    fPImpl->fState->reading++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
  }
}

void RWLock::read_lock_priority(bool block)
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  if (fPImpl->fState->writing > 0)
  {
    if (!block)
    {
      up(MUTEX);
      throw wouldblock();
    }

    fPImpl->fState->readerswaiting++;
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    down(READERS);  // unblocked by write_unlock();
#ifdef RWLOCK_DEBUG
    down(MUTEX, true);
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
#endif
  }
  else
  {
    fPImpl->fState->reading++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
  }
}

void RWLock::read_unlock()
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  /* Made this a bit more tolerant of errors b/c the lock recovery code can technically
   * be wrong.  In the practically zero chance that happens, better to take the chance
   * on a read race than a sure assertion failure
   */
  if (fPImpl->fState->reading > 0)
  {
    --fPImpl->fState->reading;

    if (fPImpl->fState->writerswaiting > 0 && fPImpl->fState->reading == 0)
    {
      --fPImpl->fState->writerswaiting;
      fPImpl->fState->writing++;
      up(WRITERS);
    }
  }

  CHECKSAFETY();
  CHECKLIVENESS();
  up(MUTEX);
}

void RWLock::write_lock(bool block)
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  if (fPImpl->fState->writing > 0 || fPImpl->fState->reading > 0)
  {
    if (!block)
    {
      up(MUTEX);
      throw wouldblock();
    }

    fPImpl->fState->writerswaiting++;
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    down(WRITERS);  // unblocked by write_unlock() or read_unlock()
#ifdef RWLOCK_DEBUG
    down(MUTEX, true);
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
#endif
  }
  else
  {
    fPImpl->fState->writing++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
  }
}

// this exists only for the sake of code cleanup
#define RETURN_STATE(mutex_state, state)                    \
  if (state)                                                \
  {                                                         \
    state->mutexLocked = mutex_state;                       \
    state->readerswaiting = fPImpl->fState->readerswaiting; \
    state->reading = fPImpl->fState->reading;               \
    state->writerswaiting = fPImpl->fState->writerswaiting; \
    state->writing = fPImpl->fState->writing;               \
  }

bool RWLock::timed_write_lock(const struct timespec& ts, struct LockState* state)
{
  bool gotIt, gotIt2;
  ptime delay;

  delay = microsec_clock::local_time() + seconds(ts.tv_sec) + microsec(ts.tv_nsec / 1000);

  gotIt = timed_down(MUTEX, delay);

  if (!gotIt)
  {
    RETURN_STATE(true, state)
    return false;
  }

  CHECKSAFETY();
  CHECKLIVENESS();

  if (fPImpl->fState->writing > 0 || fPImpl->fState->reading > 0)
  {
    fPImpl->fState->writerswaiting++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    gotIt = timed_down(WRITERS, delay);

    if (!gotIt)
    {
      // need to grab the mutex again to revoke the lock request
      // need to adjust the timeout value to make sure the attempt is made.
      delay = microsec_clock::local_time() + seconds(10);
      gotIt2 = timed_down(MUTEX, delay);

      if (!gotIt2)
      {
        RETURN_STATE(true, state);
        return false;
      }

      /* This thread could have been granted the write lock during that second
         lock grab attempt.  Observation: the thread that granted it up'd the writers sem,
         but didn't wake this thread.  If there were other writers waiting, one of those
         woke.  At this point, if writerswaiting > 0, this thread should consider itself
         one that's still waiting and should back out of the request.
         If writerswaiting == 0, this thread was the one granted the write lock, and
         needs to take possession.
       */
      if (fPImpl->fState->writerswaiting == 0)
      {
        try
        {
          down(WRITERS, false);
        }
        catch (const wouldblock&)
        {
          // Somehow another writer was able to jump in front.  This is "impossible".
          RETURN_STATE(false, state);
          up(MUTEX);
          return false;
        }

        up(MUTEX);
        return true;
      }

      fPImpl->fState->writerswaiting--;

      // need to unblock whatever was blocked by this lock attempt
      if (fPImpl->fState->writing == 0 && fPImpl->fState->writerswaiting == 0)
      {
        fPImpl->fState->reading += fPImpl->fState->readerswaiting;

        while (fPImpl->fState->readerswaiting > 0)
        {
          --fPImpl->fState->readerswaiting;
          up(READERS);
        }
      }

      // else if there's an active writer, do nothing

      CHECKSAFETY();
      CHECKLIVENESS();
      RETURN_STATE(false, state);
      up(MUTEX);
      return false;
    }
    else
      return true;
  }
  else
  {
    fPImpl->fState->writing++;
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    return true;
  }
}

void RWLock::write_unlock()
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  assert(fPImpl->fState->writing > 0);
  --fPImpl->fState->writing;

  if (fPImpl->fState->writerswaiting > 0)
  {
    --fPImpl->fState->writerswaiting;
    fPImpl->fState->writing++;
    up(WRITERS);
  }
  else if (fPImpl->fState->readerswaiting > 0)
  {
    // let up to state->readerswaiting readers go

    fPImpl->fState->reading = fPImpl->fState->readerswaiting;

    while (fPImpl->fState->readerswaiting > 0)
    {
      --fPImpl->fState->readerswaiting;
      up(READERS);
    }
  }

  CHECKSAFETY();
  CHECKLIVENESS();
  up(MUTEX);
}

void RWLock::upgrade_to_write()
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();

  /* Made this a bit more tolerant of errors b/c the lock recovery code can technically
   * be wrong.  In the practically zero chance that happens, better to take the chance
   * on a read race than a sure assertion failure
   */
  if (fPImpl->fState->reading > 0)
  {
    --fPImpl->fState->reading;

    // try to cut in line
    // On entry we hold a read lock, so reading > 0, and at this point, reading >= 0
    if (fPImpl->fState->reading == 0)
    {
      fPImpl->fState->writing++;
      CHECKSAFETY();
      CHECKLIVENESS();
      up(MUTEX);
      return;
    }
  }

  // cut & paste from write_lock()
  // The invariants hold that, on entry, writing == 0 and, by now, reading > 0, so this branch is always taken
  if (fPImpl->fState->writing > 0 || fPImpl->fState->reading > 0)
  {
    fPImpl->fState->writerswaiting++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
    down(WRITERS, true);  // unblocked by write_unlock() or read_unlock()
#ifdef RWLOCK_DEBUG
    down(MUTEX, true);
    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
#endif
  }
  else  // don't think we can get here: reading > 0 && writing == 0 && reading == 0
  {
    fPImpl->fState->writing++;

    CHECKSAFETY();
    CHECKLIVENESS();
    up(MUTEX);
  }
}

/* It's safe (and necessary) to simply convert this writer to a reader without
 blocking */
void RWLock::downgrade_to_read()
{
  down(MUTEX, true);
  CHECKSAFETY();
  CHECKLIVENESS();
  assert(fPImpl->fState->writing > 0);
  --fPImpl->fState->writing;

  if (fPImpl->fState->readerswaiting > 0)
  {
    // let up to state->readerswaiting readers go
    fPImpl->fState->reading = fPImpl->fState->readerswaiting;

    while (fPImpl->fState->readerswaiting > 0)
    {
      --fPImpl->fState->readerswaiting;
      up(READERS);
    }
  }

  fPImpl->fState->reading++;
  CHECKSAFETY();
  CHECKLIVENESS();
  up(MUTEX);
}

void RWLock::reset()
{
  fPImpl->fState->writerswaiting = 0;
  fPImpl->fState->readerswaiting = 0;
  fPImpl->fState->reading = 0;
  fPImpl->fState->writing = 0;

  for (int i = 0; i < 3; i++)
  {
    while (fPImpl->fState->sems[i].try_wait())
    {
    }
  }

  fPImpl->fState->sems[MUTEX].post();
}

LockState RWLock::getLockState()
{
  bool gotIt;
  LockState ret;

  gotIt = fPImpl->fState->sems[MUTEX].try_wait();
  ret.reading = fPImpl->fState->reading;
  ret.writing = fPImpl->fState->writing;
  ret.readerswaiting = fPImpl->fState->readerswaiting;
  ret.writerswaiting = fPImpl->fState->writerswaiting;
  ret.mutexLocked = !gotIt;

  if (gotIt)
    fPImpl->fState->sems[MUTEX].post();

  return ret;
}

}  // namespace rwlock