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Branched from the monolithic repo, Qt master branch, at commit
896db169ea224deb96c59ce8af800d019de63f12

1 files changed, 515 insertions, 0 deletions

diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp
new file mode 100644
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+/****************************************************************************
+**
+** 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.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, 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.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+**
+**
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qplatformdefs.h"
+#include "qmutex.h"
+#include <qdebug.h>
+
+#ifndef QT_NO_THREAD
+#include "qatomic.h"
+#include "qelapsedtimer.h"
+#include "qthread.h"
+#include "qmutex_p.h"
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QMutex
+    \brief The QMutex class provides access serialization between threads.
+
+    \threadsafe
+
+    \ingroup thread
+
+    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:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 0
+
+    If these two methods are called in succession, the following happens:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 1
+
+    If these two methods are called simultaneously from two threads then the
+    following sequence could result:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 2
+
+    If we add a mutex, we should get the result we want:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 3
+
+    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 static_cast<QMutexPrivate *>(d); }
+
+/*!
+    Locks the mutex. If another thread has locked the mutex then this
+    call will block until that thread has unlocked it.
+
+    Calling this function multiple times on the same mutex from the
+    same thread is allowed if this mutex is a
+    \l{QMutex::Recursive}{recursive mutex}. If this mutex is a
+    \l{QMutex::NonRecursive}{non-recursive mutex}, this function will
+    \e dead-lock when the mutex is locked recursively.
+
+    \sa unlock()
+*/
+void QMutex::lock()
+{
+    QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+    Qt::HANDLE self;
+
+    if (d->recursive) {
+        self = QThread::currentThreadId();
+        if (d->owner == self) {
+            ++d->count;
+            Q_ASSERT_X(d->count != 0, "QMutex::lock", "Overflow in recursion counter");
+            return;
+        }
+
+        bool isLocked = d->contenders.testAndSetAcquire(0, 1);
+        if (!isLocked) {
+            // didn't get the lock, wait for it
+            isLocked = d->wait();
+            Q_ASSERT_X(isLocked, "QMutex::lock",
+                       "Internal error, infinite wait has timed out.");
+        }
+
+        d->owner = self;
+        ++d->count;
+        Q_ASSERT_X(d->count != 0, "QMutex::lock", "Overflow in recursion counter");
+        return;
+    }
+
+    bool isLocked = d->contenders.testAndSetAcquire(0, 1);
+    if (!isLocked) {
+        lockInternal();
+    }
+}
+
+/*!
+    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.
+
+    Calling this function multiple times on the same mutex from the
+    same thread is allowed if this mutex is a
+    \l{QMutex::Recursive}{recursive mutex}. If this mutex is a
+    \l{QMutex::NonRecursive}{non-recursive mutex}, this function will
+    \e always return false when attempting to lock the mutex
+    recursively.
+
+    \sa lock(), unlock()
+*/
+bool QMutex::tryLock()
+{
+    QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+    Qt::HANDLE self;
+
+    if (d->recursive) {
+        self = QThread::currentThreadId();
+        if (d->owner == self) {
+            ++d->count;
+            Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
+            return true;
+        }
+
+        bool isLocked = d->contenders.testAndSetAcquire(0, 1);
+        if (!isLocked) {
+            // some other thread has the mutex locked, or we tried to
+            // recursively lock an non-recursive mutex
+            return isLocked;
+        }
+
+        d->owner = self;
+        ++d->count;
+        Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
+        return isLocked;
+    }
+
+    return d->contenders.testAndSetAcquire(0, 1);
+}
+
+/*! \overload
+
+    Attempts to lock the mutex. This function returns true if the lock
+    was obtained; otherwise it returns false. If another thread has
+    locked the mutex, this function will wait for at most \a timeout
+    milliseconds for the mutex to become available.
+
+    Note: Passing a negative number as the \a timeout is equivalent to
+    calling lock(), i.e. this function will wait forever until mutex
+    can be locked if \a timeout is negative.
+
+    If the lock was obtained, the mutex must be unlocked with unlock()
+    before another thread can successfully lock it.
+
+    Calling this function multiple times on the same mutex from the
+    same thread is allowed if this mutex is a
+    \l{QMutex::Recursive}{recursive mutex}. If this mutex is a
+    \l{QMutex::NonRecursive}{non-recursive mutex}, this function will
+    \e always return false when attempting to lock the mutex
+    recursively.
+
+    \sa lock(), unlock()
+*/
+bool QMutex::tryLock(int timeout)
+{
+    QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+    Qt::HANDLE self;
+
+    if (d->recursive) {
+        self = QThread::currentThreadId();
+        if (d->owner == self) {
+            ++d->count;
+            Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
+            return true;
+        }
+
+        bool isLocked = d->contenders.testAndSetAcquire(0, 1);
+        if (!isLocked) {
+            // didn't get the lock, wait for it
+            isLocked = d->wait(timeout);
+            if (!isLocked)
+                return false;
+        }
+
+        d->owner = self;
+        ++d->count;
+        Q_ASSERT_X(d->count != 0, "QMutex::tryLock", "Overflow in recursion counter");
+        return true;
+    }
+
+    return (d->contenders.testAndSetAcquire(0, 1)
+            // didn't get the lock, wait for it
+            || d->wait(timeout));
+}
+
+
+/*!
+    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()
+{
+    QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+    if (d->recursive) {
+        if (!--d->count) {
+            d->owner = 0;
+            if (!d->contenders.testAndSetRelease(1, 0))
+                d->wakeUp();
+        }
+    } else {
+        if (!d->contenders.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
+
+    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. You can unlock and relock the mutex with \c unlock()
+    and \c relock(). If locked, the mutex will be unlocked when the
+    QMutexLocker is destroyed.
+
+    For example, this complex function locks a QMutex upon entering
+    the function and unlocks the mutex at all the exit points:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 4
+
+    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:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 5
+
+    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 \c 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:
+
+    \snippet doc/src/snippets/code/src_corelib_thread_qmutex.cpp 6
+
+    \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. You can use \c relock() to lock
+    it again. It does not need to be locked when destroyed.
+
+    \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.
+*/
+
+/*!
+    \internal helper for lockInline()
+ */
+void QMutex::lockInternal()
+{
+    QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+
+    if (QThread::idealThreadCount() == 1) {
+        // don't spin on single cpu machines
+        bool isLocked = d->wait();
+        Q_ASSERT_X(isLocked, "QMutex::lock",
+                   "Internal error, infinite wait has timed out.");
+        Q_UNUSED(isLocked);
+        return;
+    }
+
+    QElapsedTimer elapsedTimer;
+    elapsedTimer.start();
+    do {
+        qint64 spinTime = elapsedTimer.nsecsElapsed();
+        if (spinTime > d->maximumSpinTime) {
+            // didn't get the lock, wait for it, since we're not going to gain anything by spinning more
+            elapsedTimer.start();
+            bool isLocked = d->wait();
+            Q_ASSERT_X(isLocked, "QMutex::lock",
+                       "Internal error, infinite wait has timed out.");
+            Q_UNUSED(isLocked);
+
+            qint64 maximumSpinTime = d->maximumSpinTime;
+            qint64 averageWaitTime = d->averageWaitTime;
+            qint64 actualWaitTime = elapsedTimer.nsecsElapsed();
+            if (actualWaitTime < (QMutexPrivate::MaximumSpinTimeThreshold * 3 / 2)) {
+                // measure the wait times
+                averageWaitTime = d->averageWaitTime = qMin((averageWaitTime + actualWaitTime) / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold));
+            }
+
+            // adjust the spin count when spinning does not benefit contention performance
+            if ((spinTime + actualWaitTime) - qint64(QMutexPrivate::MaximumSpinTimeThreshold) >= qint64(QMutexPrivate::MaximumSpinTimeThreshold)) {
+                // long waits, stop spinning
+                d->maximumSpinTime = 0;
+            } else {
+                // allow spinning if wait times decrease, but never spin more than the average wait time (otherwise we may perform worse)
+                d->maximumSpinTime = qBound(qint64(averageWaitTime * 3 / 2), maximumSpinTime / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold));
+            }
+            return;
+        }
+        // be a good citizen... yielding lets something else run if there is something to run, but may also relieve memory pressure if not
+        QThread::yieldCurrentThread();
+    } while (d->contenders != 0 || !d->contenders.testAndSetAcquire(0, 1));
+
+    // spinning is working, do not change the spin time (unless we are using much less time than allowed to spin)
+    qint64 maximumSpinTime = d->maximumSpinTime;
+    qint64 spinTime = elapsedTimer.nsecsElapsed();
+    if (spinTime < maximumSpinTime / 2) {
+        // we are using much less time than we need, adjust the limit
+        d->maximumSpinTime = qBound(qint64(d->averageWaitTime * 3 / 2), maximumSpinTime / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold));
+    }
+}
+
+/*!
+    \internal
+*/
+void QMutex::unlockInternal()
+{
+    static_cast<QMutexPrivate *>(d)->wakeUp();
+}
+
+/*!
+   \fn QMutex::lockInline()
+   \internal
+   inline version of QMutex::lock()
+*/
+
+/*!
+   \fn QMutex::unlockInline()
+   \internal
+   inline version of QMutex::unlock()
+*/
+
+/*!
+   \fn QMutex::tryLockInline()
+   \internal
+   inline version of QMutex::tryLock()
+*/
+
+
+QT_END_NAMESPACE
+
+#endif // QT_NO_THREAD