Windows-4.7.4/src/corelib/thread/qreadwritelock.cpp - platform/external/qt - Git at Google

 /****************************************************************************
 **
 ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
 ** All rights reserved.
 ** Contact: Nokia Corporation (qt-info@nokia.com)
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:LGPL$
 ** GNU Lesser General Public License Usage
 ** This file may be used under the terms of the GNU Lesser General Public
 ** License version 2.1 as published by the Free Software Foundation and
 ** appearing in the file LICENSE.LGPL included in the packaging of this
 ** file. Please review the following information to ensure the GNU Lesser
 ** General Public License version 2.1 requirements will be met:
 ** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
 **
 ** In addition, as a special exception, Nokia gives you certain additional
 ** rights. These rights are described in the Nokia Qt LGPL Exception
 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
 **
 ** GNU General Public License Usage
 ** Alternatively, this file may be used under the terms of the GNU General
 ** Public License version 3.0 as published by the Free Software Foundation
 ** and appearing in the file LICENSE.GPL included in the packaging of this
 ** file. Please review the following information to ensure the GNU General
 ** Public License version 3.0 requirements will be met:
 ** http://www.gnu.org/copyleft/gpl.html.
 **
 ** Other Usage
 ** Alternatively, this file may be used in accordance with the terms and
 ** conditions contained in a signed written agreement between you and Nokia.
 **
 **
 **
 **
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "qplatformdefs.h"
 #include "qreadwritelock.h"

 #ifndef QT_NO_THREAD
 #include "qmutex.h"
 #include "qthread.h"
 #include "qwaitcondition.h"

 #include "qreadwritelock_p.h"

 QT_BEGIN_NAMESPACE

 /*! \class QReadWriteLock
     \brief The QReadWriteLock class provides read-write locking.

     \threadsafe

     \ingroup thread

     A read-write lock is a synchronization tool for protecting
     resources that can be accessed for reading and writing. This type
     of lock is useful if you want to allow multiple threads to have
     simultaneous read-only access, but as soon as one thread wants to
     write to the resource, all other threads must be blocked until
     the writing is complete.

     In many cases, QReadWriteLock is a direct competitor to QMutex.
     QReadWriteLock is a good choice if there are many concurrent
     reads and writing occurs infrequently.

     Example:

     \snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 0

     To ensure that writers aren't blocked forever by readers, readers
     attempting to obtain a lock will not succeed if there is a blocked
     writer waiting for access, even if the lock is currently only
     accessed by other readers. Also, if the lock is accessed by a
     writer and another writer comes in, that writer will have
     priority over any readers that might also be waiting.

     Like QMutex, a QReadWriteLock can be recursively locked by the
     same thread when constructed in
     \l{QReadWriteLock::RecursionMode}. In such cases,
     unlock() must be called the same number of times lockForWrite() or
     lockForRead() was called. Note that the lock type cannot be
     changed when trying to lock recursively, i.e. it is not possible
     to lock for reading in a thread that already has locked for
     writing (and vice versa).

     \sa QReadLocker, QWriteLocker, QMutex, QSemaphore
 */

 /*!
     \enum QReadWriteLock::RecursionMode
     \since 4.4

     \value Recursive In this mode, a thread can lock the same
     QReadWriteLock multiple times and the mutex won't be unlocked
     until a corresponding number of unlock() calls have been made.

     \value NonRecursive In this mode, a thread may only lock a
     QReadWriteLock once.

     \sa QReadWriteLock()
 */

 /*!
     Constructs a QReadWriteLock object in NonRecursive mode.

     \sa lockForRead(), lockForWrite()
 */
 QReadWriteLock::QReadWriteLock()
     :d(new QReadWriteLockPrivate(NonRecursive))
 { }

 /*!
     \since 4.4

     Constructs a QReadWriteLock object in the given \a recursionMode.

     \sa lockForRead(), lockForWrite(), RecursionMode
 */
 QReadWriteLock::QReadWriteLock(RecursionMode recursionMode)
     : d(new QReadWriteLockPrivate(recursionMode))
 { }

 /*!
     Destroys the QReadWriteLock object.

     \warning Destroying a read-write lock that is in use may result
     in undefined behavior.
 */
 QReadWriteLock::~QReadWriteLock()
 {
     delete d;
 }

 /*!
     Locks the lock for reading. This function will block the current
     thread if any thread (including the current) has locked for
     writing.

     \sa unlock() lockForWrite() tryLockForRead()
 */
 void QReadWriteLock::lockForRead()
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
         if (it != d->currentReaders.end()) {
             ++it.value();
             ++d->accessCount;
             Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::lockForRead()",
                        "Overflow in lock counter");
             return;
         }
     }

     while (d->accessCount < 0 || d->waitingWriters) {
         ++d->waitingReaders;
         d->readerWait.wait(&d->mutex);
         --d->waitingReaders;
     }
     if (d->recursive)
         d->currentReaders.insert(self, 1);

     ++d->accessCount;
     Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::lockForRead()", "Overflow in lock counter");
 }

 /*!
     Attempts to lock for reading. If the lock was obtained, this
     function returns true, otherwise it returns false instead of
     waiting for the lock to become available, i.e. it does not block.

     The lock attempt will fail if another thread has locked for
     writing.

     If the lock was obtained, the lock must be unlocked with unlock()
     before another thread can successfully lock it.

     \sa unlock() lockForRead()
 */
 bool QReadWriteLock::tryLockForRead()
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
         if (it != d->currentReaders.end()) {
             ++it.value();
             ++d->accessCount;
             Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()",
                        "Overflow in lock counter");
             return true;
         }
     }

     if (d->accessCount < 0)
         return false;
     if (d->recursive)
         d->currentReaders.insert(self, 1);

     ++d->accessCount;
     Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()", "Overflow in lock counter");

     return true;
 }

 /*! \overload

     Attempts to lock for reading. This function returns true if the
     lock was obtained; otherwise it returns false. If another thread
     has locked for writing, this function will wait for at most \a
     timeout milliseconds for the lock to become available.

     Note: Passing a negative number as the \a timeout is equivalent to
     calling lockForRead(), i.e. this function will wait forever until
     lock can be locked for reading when \a timeout is negative.

     If the lock was obtained, the lock must be unlocked with unlock()
     before another thread can successfully lock it.

     \sa unlock() lockForRead()
 */
 bool QReadWriteLock::tryLockForRead(int timeout)
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
         if (it != d->currentReaders.end()) {
             ++it.value();
             ++d->accessCount;
             Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()",
                        "Overflow in lock counter");
             return true;
         }
     }

     while (d->accessCount < 0 || d->waitingWriters) {
         ++d->waitingReaders;
         bool success = d->readerWait.wait(&d->mutex, timeout < 0 ? ULONG_MAX : ulong(timeout));
         --d->waitingReaders;
         if (!success)
             return false;
     }
     if (d->recursive)
         d->currentReaders.insert(self, 1);

     ++d->accessCount;
     Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()", "Overflow in lock counter");

     return true;
 }

 /*!
     Locks the lock for writing. This function will block the current
     thread if another thread has locked for reading or writing.

     \sa unlock() lockForRead() tryLockForWrite()
 */
 void QReadWriteLock::lockForWrite()
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         if (d->currentWriter == self) {
             --d->accessCount;
             Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
                        "Overflow in lock counter");
             return;
         }
     }

     while (d->accessCount != 0) {
         ++d->waitingWriters;
         d->writerWait.wait(&d->mutex);
         --d->waitingWriters;
     }
     if (d->recursive)
         d->currentWriter = self;

     --d->accessCount;
     Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()", "Overflow in lock counter");
 }

 /*!
     Attempts to lock for writing. If the lock was obtained, this
     function returns true; otherwise, it returns false immediately.

     The lock attempt will fail if another thread has locked for
     reading or writing.

     If the lock was obtained, the lock must be unlocked with unlock()
     before another thread can successfully lock it.

     \sa unlock() lockForWrite()
 */
 bool QReadWriteLock::tryLockForWrite()
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         if (d->currentWriter == self) {
             --d->accessCount;
             Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
                        "Overflow in lock counter");
             return true;
         }
     }

     if (d->accessCount != 0)
         return false;
     if (d->recursive)
         d->currentWriter = self;

     --d->accessCount;
     Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::tryLockForWrite()",
                "Overflow in lock counter");

     return true;
 }

 /*! \overload

     Attempts to lock for writing. This function returns true if the
     lock was obtained; otherwise it returns false. If another thread
     has locked for reading or writing, this function will wait for at
     most \a timeout milliseconds for the lock to become available.

     Note: Passing a negative number as the \a timeout is equivalent to
     calling lockForWrite(), i.e. this function will wait forever until
     lock can be locked for writing when \a timeout is negative.

     If the lock was obtained, the lock must be unlocked with unlock()
     before another thread can successfully lock it.

     \sa unlock() lockForWrite()
 */
 bool QReadWriteLock::tryLockForWrite(int timeout)
 {
     QMutexLocker lock(&d->mutex);

     Qt::HANDLE self = 0;
     if (d->recursive) {
         self = QThread::currentThreadId();

         if (d->currentWriter == self) {
             --d->accessCount;
             Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
                        "Overflow in lock counter");
             return true;
         }
     }

     while (d->accessCount != 0) {
         ++d->waitingWriters;
         bool success = d->writerWait.wait(&d->mutex, timeout < 0 ? ULONG_MAX : ulong(timeout));
         --d->waitingWriters;

         if (!success)
             return false;
     }
     if (d->recursive)
         d->currentWriter = self;

     --d->accessCount;
     Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::tryLockForWrite()",
                "Overflow in lock counter");

     return true;
 }

 /*!
     Unlocks the lock.

     Attempting to unlock a lock that is not locked is an error, and will result
     in program termination.

     \sa lockForRead() lockForWrite() tryLockForRead() tryLockForWrite()
 */
 void QReadWriteLock::unlock()
 {
     QMutexLocker lock(&d->mutex);

     Q_ASSERT_X(d->accessCount != 0, "QReadWriteLock::unlock()", "Cannot unlock an unlocked lock");

     bool unlocked = false;
     if (d->accessCount > 0) {
         // releasing a read lock
         if (d->recursive) {
             Qt::HANDLE self = QThread::currentThreadId();
             QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
             if (it != d->currentReaders.end()) {
                 if (--it.value() <= 0)
                     d->currentReaders.erase(it);
             }
         }

         unlocked = --d->accessCount == 0;
     } else if (d->accessCount < 0 && ++d->accessCount == 0) {
         // released a write lock
         unlocked = true;
         d->currentWriter = 0;
     }

     if (unlocked) {
         if (d->waitingWriters) {
             d->writerWait.wakeOne();
         } else if (d->waitingReaders) {
             d->readerWait.wakeAll();
         }
     }
 }

 /*!
     \class QReadLocker
     \brief The QReadLocker class is a convenience class that
     simplifies locking and unlocking read-write locks for read access.

     \threadsafe

     \ingroup thread

     The purpose of QReadLocker (and QWriteLocker) is to simplify
     QReadWriteLock locking and unlocking. Locking and unlocking
     statements or in exception handling code is error-prone and
     difficult to debug. QReadLocker can be used in such situations
     to ensure that the state of the lock is always well-defined.

     Here's an example that uses QReadLocker to lock and unlock a
     read-write lock for reading:

     \snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 1

     It is equivalent to the following code:

     \snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 2

     The QMutexLocker documentation shows examples where the use of a
     locker object greatly simplifies programming.

     \sa QWriteLocker, QReadWriteLock
 */

 /*!
     \fn QReadLocker::QReadLocker(QReadWriteLock *lock)

     Constructs a QReadLocker and locks \a lock for reading. The lock
     will be unlocked when the QReadLocker is destroyed. If \c lock is
     zero, QReadLocker does nothing.

     \sa QReadWriteLock::lockForRead()
 */

 /*!
     \fn QReadLocker::~QReadLocker()

     Destroys the QReadLocker and unlocks the lock that was passed to
     the constructor.

     \sa QReadWriteLock::unlock()
 */

 /*!
     \fn void QReadLocker::unlock()

     Unlocks the lock associated with this locker.

     \sa QReadWriteLock::unlock()
 */

 /*!
     \fn void QReadLocker::relock()

     Relocks an unlocked lock.

     \sa unlock()
 */

 /*!
     \fn QReadWriteLock *QReadLocker::readWriteLock() const

     Returns a pointer to the read-write lock that was passed
     to the constructor.
 */

 /*!
     \class QWriteLocker
     \brief The QWriteLocker class is a convenience class that
     simplifies locking and unlocking read-write locks for write access.

     \threadsafe

     \ingroup thread

     The purpose of QWriteLocker (and QReadLocker is to simplify
     QReadWriteLock locking and unlocking. Locking and unlocking
     statements or in exception handling code is error-prone and
     difficult to debug. QWriteLocker can be used in such situations
     to ensure that the state of the lock is always well-defined.

     Here's an example that uses QWriteLocker to lock and unlock a
     read-write lock for writing:

     \snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 3

     It is equivalent to the following code:

     \snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 4

     The QMutexLocker documentation shows examples where the use of a
     locker object greatly simplifies programming.

     \sa QReadLocker, QReadWriteLock
 */

 /*!
     \fn QWriteLocker::QWriteLocker(QReadWriteLock *lock)

     Constructs a QWriteLocker and locks \a lock for writing. The lock
     will be unlocked when the QWriteLocker is destroyed. If \c lock is
     zero, QWriteLocker does nothing.

     \sa QReadWriteLock::lockForWrite()
 */

 /*!
     \fn QWriteLocker::~QWriteLocker()

     Destroys the QWriteLocker and unlocks the lock that was passed to
     the constructor.

     \sa QReadWriteLock::unlock()
 */

 /*!
     \fn void QWriteLocker::unlock()

     Unlocks the lock associated with this locker.

     \sa QReadWriteLock::unlock()
 */

 /*!
     \fn void QWriteLocker::relock()

     Relocks an unlocked lock.

     \sa unlock()
 */

 /*!
     \fn QReadWriteLock *QWriteLocker::readWriteLock() const

     Returns a pointer to the read-write lock that was passed
     to the constructor.
 */

 QT_END_NAMESPACE

 #endif // QT_NO_THREAD
	/****************************************************************************
	**
	** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
	** All rights reserved.
	** Contact: Nokia Corporation (qt-info@nokia.com)
	**
	** This file is part of the QtCore module of the Qt Toolkit.
	**
	** $QT_BEGIN_LICENSE:LGPL$
	** GNU Lesser General Public License Usage
	** This file may be used under the terms of the GNU Lesser General Public
	** License version 2.1 as published by the Free Software Foundation and
	** appearing in the file LICENSE.LGPL included in the packaging of this
	** file. Please review the following information to ensure the GNU Lesser
	** General Public License version 2.1 requirements will be met:
	** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
	**
	** In addition, as a special exception, Nokia gives you certain additional
	** rights. These rights are described in the Nokia Qt LGPL Exception
	** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
	**
	** GNU General Public License Usage
	** Alternatively, this file may be used under the terms of the GNU General
	** Public License version 3.0 as published by the Free Software Foundation
	** and appearing in the file LICENSE.GPL included in the packaging of this
	** file. Please review the following information to ensure the GNU General
	** Public License version 3.0 requirements will be met:
	** http://www.gnu.org/copyleft/gpl.html.
	**
	** Other Usage
	** Alternatively, this file may be used in accordance with the terms and
	** conditions contained in a signed written agreement between you and Nokia.
	**
	**
	**
	**
	**
	** $QT_END_LICENSE$
	**
	****************************************************************************/

	#include "qplatformdefs.h"
	#include "qreadwritelock.h"

	#ifndef QT_NO_THREAD
	#include "qmutex.h"
	#include "qthread.h"
	#include "qwaitcondition.h"

	#include "qreadwritelock_p.h"

	QT_BEGIN_NAMESPACE

	/*! \class QReadWriteLock
	\brief The QReadWriteLock class provides read-write locking.

	\threadsafe

	\ingroup thread

	A read-write lock is a synchronization tool for protecting
	resources that can be accessed for reading and writing. This type
	of lock is useful if you want to allow multiple threads to have
	simultaneous read-only access, but as soon as one thread wants to
	write to the resource, all other threads must be blocked until
	the writing is complete.

	In many cases, QReadWriteLock is a direct competitor to QMutex.
	QReadWriteLock is a good choice if there are many concurrent
	reads and writing occurs infrequently.

	Example:

	\snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 0

	To ensure that writers aren't blocked forever by readers, readers
	attempting to obtain a lock will not succeed if there is a blocked
	writer waiting for access, even if the lock is currently only
	accessed by other readers. Also, if the lock is accessed by a
	writer and another writer comes in, that writer will have
	priority over any readers that might also be waiting.

	Like QMutex, a QReadWriteLock can be recursively locked by the
	same thread when constructed in
	\l{QReadWriteLock::RecursionMode}. In such cases,
	unlock() must be called the same number of times lockForWrite() or
	lockForRead() was called. Note that the lock type cannot be
	changed when trying to lock recursively, i.e. it is not possible
	to lock for reading in a thread that already has locked for
	writing (and vice versa).

	\sa QReadLocker, QWriteLocker, QMutex, QSemaphore
	*/

	/*!
	\enum QReadWriteLock::RecursionMode
	\since 4.4

	\value Recursive In this mode, a thread can lock the same
	QReadWriteLock multiple times and the mutex won't be unlocked
	until a corresponding number of unlock() calls have been made.

	\value NonRecursive In this mode, a thread may only lock a
	QReadWriteLock once.

	\sa QReadWriteLock()
	*/

	/*!
	Constructs a QReadWriteLock object in NonRecursive mode.

	\sa lockForRead(), lockForWrite()
	*/
	QReadWriteLock::QReadWriteLock()
	:d(new QReadWriteLockPrivate(NonRecursive))
	{ }

	/*!
	\since 4.4

	Constructs a QReadWriteLock object in the given \a recursionMode.

	\sa lockForRead(), lockForWrite(), RecursionMode
	*/
	QReadWriteLock::QReadWriteLock(RecursionMode recursionMode)
	: d(new QReadWriteLockPrivate(recursionMode))
	{ }

	/*!
	Destroys the QReadWriteLock object.

	\warning Destroying a read-write lock that is in use may result
	in undefined behavior.
	*/
	QReadWriteLock::~QReadWriteLock()
	{
	delete d;
	}

	/*!
	Locks the lock for reading. This function will block the current
	thread if any thread (including the current) has locked for
	writing.

	\sa unlock() lockForWrite() tryLockForRead()
	*/
	void QReadWriteLock::lockForRead()
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
	if (it != d->currentReaders.end()) {
	++it.value();
	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::lockForRead()",
	"Overflow in lock counter");
	return;
	}
	}

	while (d->accessCount < 0 \|\| d->waitingWriters) {
	++d->waitingReaders;
	d->readerWait.wait(&d->mutex);
	--d->waitingReaders;
	}
	if (d->recursive)
	d->currentReaders.insert(self, 1);

	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::lockForRead()", "Overflow in lock counter");
	}

	/*!
	Attempts to lock for reading. If the lock was obtained, this
	function returns true, otherwise it returns false instead of
	waiting for the lock to become available, i.e. it does not block.

	The lock attempt will fail if another thread has locked for
	writing.

	If the lock was obtained, the lock must be unlocked with unlock()
	before another thread can successfully lock it.

	\sa unlock() lockForRead()
	*/
	bool QReadWriteLock::tryLockForRead()
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
	if (it != d->currentReaders.end()) {
	++it.value();
	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()",
	"Overflow in lock counter");
	return true;
	}
	}

	if (d->accessCount < 0)
	return false;
	if (d->recursive)
	d->currentReaders.insert(self, 1);

	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()", "Overflow in lock counter");

	return true;
	}

	/*! \overload

	Attempts to lock for reading. This function returns true if the
	lock was obtained; otherwise it returns false. If another thread
	has locked for writing, this function will wait for at most \a
	timeout milliseconds for the lock to become available.

	Note: Passing a negative number as the \a timeout is equivalent to
	calling lockForRead(), i.e. this function will wait forever until
	lock can be locked for reading when \a timeout is negative.

	If the lock was obtained, the lock must be unlocked with unlock()
	before another thread can successfully lock it.

	\sa unlock() lockForRead()
	*/
	bool QReadWriteLock::tryLockForRead(int timeout)
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
	if (it != d->currentReaders.end()) {
	++it.value();
	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()",
	"Overflow in lock counter");
	return true;
	}
	}

	while (d->accessCount < 0 \|\| d->waitingWriters) {
	++d->waitingReaders;
	bool success = d->readerWait.wait(&d->mutex, timeout < 0 ? ULONG_MAX : ulong(timeout));
	--d->waitingReaders;
	if (!success)
	return false;
	}
	if (d->recursive)
	d->currentReaders.insert(self, 1);

	++d->accessCount;
	Q_ASSERT_X(d->accessCount > 0, "QReadWriteLock::tryLockForRead()", "Overflow in lock counter");

	return true;
	}

	/*!
	Locks the lock for writing. This function will block the current
	thread if another thread has locked for reading or writing.

	\sa unlock() lockForRead() tryLockForWrite()
	*/
	void QReadWriteLock::lockForWrite()
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	if (d->currentWriter == self) {
	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
	"Overflow in lock counter");
	return;
	}
	}

	while (d->accessCount != 0) {
	++d->waitingWriters;
	d->writerWait.wait(&d->mutex);
	--d->waitingWriters;
	}
	if (d->recursive)
	d->currentWriter = self;

	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()", "Overflow in lock counter");
	}

	/*!
	Attempts to lock for writing. If the lock was obtained, this
	function returns true; otherwise, it returns false immediately.

	The lock attempt will fail if another thread has locked for
	reading or writing.

	If the lock was obtained, the lock must be unlocked with unlock()
	before another thread can successfully lock it.

	\sa unlock() lockForWrite()
	*/
	bool QReadWriteLock::tryLockForWrite()
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	if (d->currentWriter == self) {
	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
	"Overflow in lock counter");
	return true;
	}
	}

	if (d->accessCount != 0)
	return false;
	if (d->recursive)
	d->currentWriter = self;

	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::tryLockForWrite()",
	"Overflow in lock counter");

	return true;
	}

	/*! \overload

	Attempts to lock for writing. This function returns true if the
	lock was obtained; otherwise it returns false. If another thread
	has locked for reading or writing, this function will wait for at
	most \a timeout milliseconds for the lock to become available.

	Note: Passing a negative number as the \a timeout is equivalent to
	calling lockForWrite(), i.e. this function will wait forever until
	lock can be locked for writing when \a timeout is negative.

	If the lock was obtained, the lock must be unlocked with unlock()
	before another thread can successfully lock it.

	\sa unlock() lockForWrite()
	*/
	bool QReadWriteLock::tryLockForWrite(int timeout)
	{
	QMutexLocker lock(&d->mutex);

	Qt::HANDLE self = 0;
	if (d->recursive) {
	self = QThread::currentThreadId();

	if (d->currentWriter == self) {
	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::lockForWrite()",
	"Overflow in lock counter");
	return true;
	}
	}

	while (d->accessCount != 0) {
	++d->waitingWriters;
	bool success = d->writerWait.wait(&d->mutex, timeout < 0 ? ULONG_MAX : ulong(timeout));
	--d->waitingWriters;

	if (!success)
	return false;
	}
	if (d->recursive)
	d->currentWriter = self;

	--d->accessCount;
	Q_ASSERT_X(d->accessCount < 0, "QReadWriteLock::tryLockForWrite()",
	"Overflow in lock counter");

	return true;
	}

	/*!
	Unlocks the lock.

	Attempting to unlock a lock that is not locked is an error, and will result
	in program termination.

	\sa lockForRead() lockForWrite() tryLockForRead() tryLockForWrite()
	*/
	void QReadWriteLock::unlock()
	{
	QMutexLocker lock(&d->mutex);

	Q_ASSERT_X(d->accessCount != 0, "QReadWriteLock::unlock()", "Cannot unlock an unlocked lock");

	bool unlocked = false;
	if (d->accessCount > 0) {
	// releasing a read lock
	if (d->recursive) {
	Qt::HANDLE self = QThread::currentThreadId();
	QHash<Qt::HANDLE, int>::iterator it = d->currentReaders.find(self);
	if (it != d->currentReaders.end()) {
	if (--it.value() <= 0)
	d->currentReaders.erase(it);
	}
	}

	unlocked = --d->accessCount == 0;
	} else if (d->accessCount < 0 && ++d->accessCount == 0) {
	// released a write lock
	unlocked = true;
	d->currentWriter = 0;
	}

	if (unlocked) {
	if (d->waitingWriters) {
	d->writerWait.wakeOne();
	} else if (d->waitingReaders) {
	d->readerWait.wakeAll();
	}
	}
	}

	/*!
	\class QReadLocker
	\brief The QReadLocker class is a convenience class that
	simplifies locking and unlocking read-write locks for read access.

	\threadsafe

	\ingroup thread

	The purpose of QReadLocker (and QWriteLocker) is to simplify
	QReadWriteLock locking and unlocking. Locking and unlocking
	statements or in exception handling code is error-prone and
	difficult to debug. QReadLocker can be used in such situations
	to ensure that the state of the lock is always well-defined.

	Here's an example that uses QReadLocker to lock and unlock a
	read-write lock for reading:

	\snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 1

	It is equivalent to the following code:

	\snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 2

	The QMutexLocker documentation shows examples where the use of a
	locker object greatly simplifies programming.

	\sa QWriteLocker, QReadWriteLock
	*/

	/*!
	\fn QReadLocker::QReadLocker(QReadWriteLock *lock)

	Constructs a QReadLocker and locks \a lock for reading. The lock
	will be unlocked when the QReadLocker is destroyed. If \c lock is
	zero, QReadLocker does nothing.

	\sa QReadWriteLock::lockForRead()
	*/

	/*!
	\fn QReadLocker::~QReadLocker()

	Destroys the QReadLocker and unlocks the lock that was passed to
	the constructor.

	\sa QReadWriteLock::unlock()
	*/

	/*!
	\fn void QReadLocker::unlock()

	Unlocks the lock associated with this locker.

	\sa QReadWriteLock::unlock()
	*/

	/*!
	\fn void QReadLocker::relock()

	Relocks an unlocked lock.

	\sa unlock()
	*/

	/*!
	\fn QReadWriteLock *QReadLocker::readWriteLock() const

	Returns a pointer to the read-write lock that was passed
	to the constructor.
	*/

	/*!
	\class QWriteLocker
	\brief The QWriteLocker class is a convenience class that
	simplifies locking and unlocking read-write locks for write access.

	\threadsafe

	\ingroup thread

	The purpose of QWriteLocker (and QReadLocker is to simplify
	QReadWriteLock locking and unlocking. Locking and unlocking
	statements or in exception handling code is error-prone and
	difficult to debug. QWriteLocker can be used in such situations
	to ensure that the state of the lock is always well-defined.

	Here's an example that uses QWriteLocker to lock and unlock a
	read-write lock for writing:

	\snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 3

	It is equivalent to the following code:

	\snippet doc/src/snippets/code/src_corelib_thread_qreadwritelock.cpp 4

	The QMutexLocker documentation shows examples where the use of a
	locker object greatly simplifies programming.

	\sa QReadLocker, QReadWriteLock
	*/

	/*!
	\fn QWriteLocker::QWriteLocker(QReadWriteLock *lock)

	Constructs a QWriteLocker and locks \a lock for writing. The lock
	will be unlocked when the QWriteLocker is destroyed. If \c lock is
	zero, QWriteLocker does nothing.

	\sa QReadWriteLock::lockForWrite()
	*/

	/*!
	\fn QWriteLocker::~QWriteLocker()

	Destroys the QWriteLocker and unlocks the lock that was passed to
	the constructor.

	\sa QReadWriteLock::unlock()
	*/

	/*!
	\fn void QWriteLocker::unlock()

	Unlocks the lock associated with this locker.

	\sa QReadWriteLock::unlock()
	*/

	/*!
	\fn void QWriteLocker::relock()

	Relocks an unlocked lock.

	\sa unlock()
	*/

	/*!
	\fn QReadWriteLock *QWriteLocker::readWriteLock() const

	Returns a pointer to the read-write lock that was passed
	to the constructor.
	*/

	QT_END_NAMESPACE

	#endif // QT_NO_THREAD