/******************************************************************************** Copyright (C) 1992-2006 Trolltech ASA. All rights reserved.**** This file is part of the QtCore module of the Qt Toolkit.**** This file may be used under the terms of the GNU General Public** License version 2.0 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 GNU** General Public Licensing requirements will be met:** http://www.trolltech.com/products/qt/opensource.html**** If you are unsure which license is appropriate for your use, please** review the following information:** http://www.trolltech.com/products/qt/licensing.html or contact the** sales department at sales@trolltech.com.**** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.******************************************************************************/#include "qplatformdefs.h"#include "qmutex.h"#ifndef QT_NO_THREAD#include "qatomic.h"#include "qmutex_p.h"/*!    \class QMutex    \brief The QMutex class provides access serialization between threads.    \threadsafe    \ingroup thread    \ingroup environment    \mainclass    The purpose of a QMutex is to protect an object, data structure or    section of code so that only one thread can access it at a time    (this is similar to the Java \c synchronized keyword). It is    usually best to use a mutex with a QMutexLocker since this makes    it easy to ensure that locking and unlocking are performed    consistently.    For example, say there is a method that prints a message to the    user on two lines:    \code        int number = 6;        void method1()        {            number *= 5;            number /= 4;        }        void method2()        {            number *= 3;            number /= 2;        }    \endcode    If these two methods are called in succession, the following happens:    \code        // method1()        number *= 5;        // number is now 30        number /= 4;        // number is now 7        // method2()        number *= 3;        // number is now 21        number /= 2;        // number is now 10    \endcode    If these two methods are called simultaneously from two threads then the    following sequence could result:    \code        // Thread 1 calls method1()        number *= 5;        // number is now 30        // Thread 2 calls method2().        //        // Most likely Thread 1 has been put to sleep by the operating        // system to allow Thread 2 to run.        number *= 3;        // number is now 90        number /= 2;        // number is now 45        // Thread 1 finishes executing.        number /= 4;        // number is now 11, instead of 10    \endcode    If we add a mutex, we should get the result we want:    \code        QMutex mutex;        int number = 6;        void method1()        {            mutex.lock();            number *= 5;            number /= 4;            mutex.unlock();        }        void method2()        {            mutex.lock();            number *= 3;            number /= 2;            mutex.unlock();        }    \endcode    Then only one thread can modify \c number at any given time and    the result is correct. This is a trivial example, of course, but    applies to any other case where things need to happen in a    particular sequence.    When you call lock() in a thread, other threads that try to call    lock() in the same place will block until the thread that got the    lock calls unlock(). A non-blocking alternative to lock() is    tryLock().    \sa QMutexLocker, QReadWriteLock, QSemaphore, QWaitCondition*//*!    \enum QMutex::RecursionMode    \value Recursive  In this mode, a thread can lock the same mutex                      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 mutex                         once.    \sa QMutex()*//*!    Constructs a new mutex. The mutex is created in an unlocked state.    If \a mode is QMutex::Recursive, a thread can lock the same mutex    multiple times and the mutex won't be unlocked until a    corresponding number of unlock() calls have been made. The    default is QMutex::NonRecursive.    \sa lock(), unlock()*/QMutex::QMutex(RecursionMode mode)    : d(new QMutexPrivate(mode)){ }/*!    Destroys the mutex.    \warning Destroying a locked mutex may result in undefined behavior.*/QMutex::~QMutex(){ delete d; }/*!    Locks the mutex. If another thread has locked the mutex then this    call will block until that thread has unlocked it.    \sa unlock()*/void QMutex::lock(){    ulong self = d->self();    int sentinel;    forever {        sentinel = d->lock;        if (d->lock.testAndSetAcquire(sentinel, sentinel + 1))            break;    }    if (sentinel != 0) {        if (!d->recursive || d->owner != self) {            if (d->owner == self) {                qWarning("QMutex::lock: Deadlock detected in thread %ld", d->owner);            }            // didn't get the lock, wait for it            d->wait();        }        // don't need to wait for the lock anymore        d->lock.deref();    }    d->owner = self;    ++d->count;    Q_ASSERT_X(d->count != 0, "QMutex::lock", "Overflow in recursion counter");}/*!    Attempts to lock the mutex. If the lock was obtained, this function    returns true. If another thread has locked the mutex, this    function returns false immediately.    If the lock was obtained, the mutex must be unlocked with unlock()    before another thread can successfully lock it.    \sa lock(), unlock()*/bool QMutex::tryLock(){    ulong self = d->self();    int sentinel;    forever {        sentinel = d->lock;        if (d->lock.testAndSetAcquire(sentinel, sentinel + 1))            break;    }    if (sentinel != 0) {        // we're not going to wait for lock        d->lock.deref();        if (!d->recursive || d->owner != self) {            // some other thread has the mutex locked, or we tried to            // recursively lock an non-recursive mutex            return false;        }    }    d->owner = self;    ++d->count;    return true;}/*!    Unlocks the mutex. Attempting to unlock a mutex in a different    thread to the one that locked it results in an error. Unlocking a    mutex that is not locked results in undefined behavior.    \sa lock()*/void QMutex::unlock(){    Q_ASSERT_X(d->owner == d->self(), "QMutex::unlock()",               "A mutex must be unlocked in the same thread that locked it.");    if (!--d->count) {        d->owner = 0;        if (!d->lock.testAndSetRelease(1, 0))            d->wakeUp();    }}/*!    \fn bool QMutex::locked()    Returns true if the mutex is locked by another thread; otherwise    returns false.    It is generally a bad idea to use this function, because code    that uses it has a race condition. Use tryLock() and unlock()    instead.    \oldcode        bool isLocked = mutex.locked();    \newcode        bool isLocked = true;        if (mutex.tryLock()) {            mutex.unlock();            isLocked = false;        }    \endcode*//*!    \class QMutexLocker    \brief The QMutexLocker class is a convenience class that simplifies    locking and unlocking mutexes.    \threadsafe    \ingroup thread    \ingroup environment    The purpose of QMutexLocker is to simplify QMutex locking and    unlocking. Locking and unlocking a QMutex in complex functions and    statements or in exception handling code is error-prone and    difficult to debug. QMutexLocker can be used in such situations    to ensure that the state of the mutex is always well-defined.    QMutexLocker should be created within a function where a QMutex    needs to be locked. The mutex is locked when QMutexLocker is    created, and unlocked when QMutexLocker is destroyed.    For example, this complex function locks a QMutex upon entering    the function and unlocks the mutex at all the exit points:    \code        int complexFunction(int flag)        {            mutex.lock();            int retVal = 0;            switch (flag) {            case 0:            case 1:                mutex.unlock();                return moreComplexFunction(flag);            case 2:                {                    int status = anotherFunction();                    if (status < 0) {                        mutex.unlock();                        return -2;                    }                    retVal = status + flag;                }                break;            default:                if (flag > 10) {                    mutex.unlock();                    return -1;                }                break;            }            mutex.unlock();            return retVal;        }    \endcode    This example function will get more complicated as it is    developed, which increases the likelihood that errors will occur.    Using QMutexLocker greatly simplifies the code, and makes it more    readable:    \code        int complexFunction(int flag)        {            QMutexLocker locker(&mutex);            int retVal = 0;            switch (flag) {            case 0:            case 1:                return moreComplexFunction(flag);            case 2:                {                    int status = anotherFunction();                    if (status < 0)                        return -2;                    retVal = status + flag;                }                break;            default:                if (flag > 10)                    return -1;                break;            }            return retVal;        }    \endcode    Now, the mutex will always be unlocked when the QMutexLocker    object is destroyed (when the function returns since \c locker is    an auto variable).    The same principle applies to code that throws and catches    exceptions. An exception that is not caught in the function that    has locked the mutex has no way of unlocking the mutex before the    exception is passed up the stack to the calling function.    QMutexLocker also provides a mutex() member function that returns    the mutex on which the QMutexLocker is operating. This is useful    for code that needs access to the mutex, such as    QWaitCondition::wait(). For example:    \code        class SignalWaiter        {        private:            QMutexLocker locker;        public:            SignalWaiter(QMutex *mutex)                : locker(mutex)            {            }            void waitForSignal()            {                ...                while (!signalled)                    waitCondition.wait(locker.mutex());                ...            }        };    \endcode    \sa QReadLocker, QWriteLocker, QMutex*//*!    \fn QMutexLocker::QMutexLocker(QMutex *mutex)    Constructs a QMutexLocker and locks \a mutex. The mutex will be    unlocked when the QMutexLocker is destroyed. If \a mutex is zero,    QMutexLocker does nothing.    \sa QMutex::lock()*//*!    \fn QMutexLocker::~QMutexLocker()    Destroys the QMutexLocker and unlocks the mutex that was locked    in the constructor.    \sa QMutex::unlock()*//*!    \fn QMutex *QMutexLocker::mutex() const    Returns a pointer to the mutex that was locked in the    constructor.*//*!    \fn void QMutexLocker::unlock()    Unlocks this mutex locker.    \sa relock()*//*!    \fn void QMutexLocker::relock()    Relocks an unlocked mutex locker.    \sa unlock()*//*!    \fn QMutex::QMutex(bool recursive)    Use the constructor that takes a RecursionMode parameter instead.*/#endif // QT_NO_THREAD