arangodb/lib/Basics/ReadWriteLock.cpp

////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Frank Celler
/// @author Achim Brandt
////////////////////////////////////////////////////////////////////////////////

#include "ReadWriteLock.h"

using namespace triagens::basics;


////////////////////////////////////////////////////////////////////////////////
/// @brief constructs a read-write lock
////////////////////////////////////////////////////////////////////////////////

ReadWriteLock::ReadWriteLock() : _rwlock(), _writeLocked(false) {
  TRI_InitReadWriteLock(&_rwlock);

#ifdef TRI_READ_WRITE_LOCK_COUNTER
  TRI_InitMutex(&_mutex);

  _readLockedCounter = 0;
  _writeLockedCounter = 0;
#endif
}

////////////////////////////////////////////////////////////////////////////////
/// @brief deletes read-write lock
////////////////////////////////////////////////////////////////////////////////

ReadWriteLock::~ReadWriteLock() {
  TRI_DestroyReadWriteLock(&_rwlock);

#ifdef TRI_READ_WRITE_LOCK_COUNTER
  TRI_DestroyMutex(&_mutex);
#endif
}


////////////////////////////////////////////////////////////////////////////////
/// @brief check for read locked
////////////////////////////////////////////////////////////////////////////////

#ifdef TRI_READ_WRITE_LOCK_COUNTER

bool ReadWriteLock::isReadLocked() const { return _readLockedCounter > 0; }

#endif

////////////////////////////////////////////////////////////////////////////////
/// @brief locks for reading
////////////////////////////////////////////////////////////////////////////////

void ReadWriteLock::readLock() {
  TRI_ReadLockReadWriteLock(&_rwlock);

#ifdef TRI_READ_WRITE_LOCK_COUNTER

  TRI_LockMutex(&_mutex);
  _readLockedCounter++;
  TRI_UnlockMutex(&_mutex);

#endif
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tries to lock for reading
////////////////////////////////////////////////////////////////////////////////

bool ReadWriteLock::tryReadLock() {
  if (!TRI_TryReadLockReadWriteLock(&_rwlock)) {
    return false;
  }

#ifdef TRI_READ_WRITE_LOCK_COUNTER

  TRI_LockMutex(&_mutex);
  _readLockedCounter++;
  TRI_UnlockMutex(&_mutex);

#endif
  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief check for write locked
////////////////////////////////////////////////////////////////////////////////

#ifdef TRI_READ_WRITE_LOCK_COUNTER

bool ReadWriteLock::isWriteLocked() const { return _writeLockedCounter > 0; }

#endif

////////////////////////////////////////////////////////////////////////////////
/// @brief locks for writing
////////////////////////////////////////////////////////////////////////////////

void ReadWriteLock::writeLock() {
  TRI_WriteLockReadWriteLock(&_rwlock);

  _writeLocked = true;

#ifdef TRI_READ_WRITE_LOCK_COUNTER

  TRI_LockMutex(&_mutex);
  _writeLockedCounter++;
  TRI_UnlockMutex(&_mutex);

#endif
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tries to lock for writing
////////////////////////////////////////////////////////////////////////////////

bool ReadWriteLock::tryWriteLock() {
  if (!TRI_TryWriteLockReadWriteLock(&_rwlock)) {
    return false;
  }

  _writeLocked = true;

#ifdef TRI_READ_WRITE_LOCK_COUNTER

  TRI_LockMutex(&_mutex);
  _writeLockedCounter++;
  TRI_UnlockMutex(&_mutex);

#endif
  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief releases the read-lock or write-lock
////////////////////////////////////////////////////////////////////////////////

void ReadWriteLock::unlock() {
#ifdef TRI_READ_WRITE_LOCK_COUNTER

  TRI_LockMutex(&_mutex);

  if (_writeLocked) {
    _writeLockedCounter--;
  } else {
    _readLockedCounter--;
  }

  TRI_UnlockMutex(&_mutex);

#endif

  if (_writeLocked) {
    _writeLocked = false;
    TRI_WriteUnlockReadWriteLock(&_rwlock);
  } else {
    TRI_ReadUnlockReadWriteLock(&_rwlock);
  }
}