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+/****************************************************************************
+**
+** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/
+**
+** 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.
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QTCONCURRENT_THREADENGINE_H
+#define QTCONCURRENT_THREADENGINE_H
+
+#include <QtCore/qglobal.h>
+
+#ifndef QT_NO_CONCURRENT
+
+#include <QtCore/qthreadpool.h>
+#include <QtConcurrent/qfuture.h>
+#include <QtCore/qdebug.h>
+#include <QtConcurrent/qtconcurrentexception.h>
+#include <QtCore/qwaitcondition.h>
+#include <QtCore/qatomic.h>
+#include <QtCore/qsemaphore.h>
+
+QT_BEGIN_HEADER
+QT_BEGIN_NAMESPACE
+
+
+#ifndef qdoc
+
+namespace QtConcurrent {
+
+// The ThreadEngineBarrier counts worker threads, and allows one
+// thread to wait for all others to finish. Tested for its use in
+// QtConcurrent, requires more testing for use as a general class.
+class ThreadEngineBarrier
+{
+private:
+    // The thread count is maintained as an integer in the count atomic
+    // variable. The count can be either positive or negative - a negative
+    // count signals that a thread is waiting on the barrier.
+
+    // BC note: inlined code from Qt < 4.6 will expect to find the QMutex 
+    // and QAtomicInt here. ### Qt 5: remove.
+    QMutex mutex;
+    QAtomicInt count;
+
+    QSemaphore semaphore;
+public:
+    ThreadEngineBarrier();
+    void acquire();
+    int release();
+    void wait();
+    int currentCount();
+    bool releaseUnlessLast();
+};
+
+enum ThreadFunctionResult { ThrottleThread, ThreadFinished };
+
+// The ThreadEngine controls the threads used in the computation.
+// Can be run in three modes: single threaded, multi-threaded blocking
+// and multi-threaded asynchronous.
+// The code for the single threaded mode is
+class Q_CORE_EXPORT ThreadEngineBase: public QRunnable
+{
+public:
+    // Public API:
+    ThreadEngineBase();
+    virtual ~ThreadEngineBase();
+    void startSingleThreaded();
+    void startBlocking();
+    void startThread();
+    bool isCanceled();
+    void waitForResume();
+    bool isProgressReportingEnabled();
+    void setProgressValue(int progress);
+    void setProgressRange(int minimum, int maximum);
+    void acquireBarrierSemaphore();
+
+protected: // The user overrides these:
+    virtual void start() {}
+    virtual void finish() {}
+    virtual ThreadFunctionResult threadFunction() { return ThreadFinished; }
+    virtual bool shouldStartThread() { return futureInterface ? !futureInterface->isPaused() : true; }
+    virtual bool shouldThrottleThread() { return futureInterface ? futureInterface->isPaused() : false; }
+private:
+    bool startThreadInternal();
+    void startThreads();
+    void threadExit();
+    bool threadThrottleExit();
+    void run();
+    virtual void asynchronousFinish() = 0;
+#ifndef QT_NO_EXCEPTIONS
+    void handleException(const QtConcurrent::Exception &exception);
+#endif
+protected:
+    QFutureInterfaceBase *futureInterface;
+    QThreadPool *threadPool;
+    ThreadEngineBarrier barrier;
+    QtConcurrent::internal::ExceptionStore exceptionStore;
+};
+
+
+template <typename T>
+class ThreadEngine : public virtual ThreadEngineBase
+{
+public:
+    typedef T ResultType;
+
+    virtual T *result() { return 0; }
+
+    QFutureInterface<T> *futureInterfaceTyped()
+    {
+        return static_cast<QFutureInterface<T> *>(futureInterface);
+    }
+
+    // Runs the user algorithm using a single thread.
+    T *startSingleThreaded()
+    {
+        ThreadEngineBase::startSingleThreaded();
+        return result();
+    }
+
+    // Runs the user algorithm using multiple threads.
+    // This function blocks until the algorithm is finished,
+    // and then returns the result.
+    T *startBlocking()
+    {
+        ThreadEngineBase::startBlocking();
+        return result();
+    }
+
+    // Runs the user algorithm using multiple threads.
+    // Does not block, returns a future.
+    QFuture<T> startAsynchronously()
+    {
+        futureInterface = new QFutureInterface<T>();
+
+        // reportStart() must be called before starting threads, otherwise the
+        // user algorithm might finish while reportStart() is running, which
+        // is very bad.
+        futureInterface->reportStarted();
+        QFuture<T> future = QFuture<T>(futureInterfaceTyped());
+        start();
+
+        acquireBarrierSemaphore();
+        threadPool->start(this);
+        return future;
+    }
+
+    void asynchronousFinish()
+    {
+        finish();
+        futureInterfaceTyped()->reportFinished(result());
+        delete futureInterfaceTyped();
+        delete this;
+    }
+
+
+    void reportResult(const T *_result, int index = -1)
+    {
+        if (futureInterface)
+            futureInterfaceTyped()->reportResult(_result, index);
+    }
+
+    void reportResults(const QVector<T> &_result, int index = -1, int count = -1)
+    {
+        if (futureInterface)
+            futureInterfaceTyped()->reportResults(_result, index, count);
+    }
+};
+
+// The ThreadEngineStarter class ecapsulates the return type
+// from the thread engine.
+// Depending on how the it is used, it will run
+// the engine in either blocking mode or asynchronous mode.
+template <typename T>
+class ThreadEngineStarterBase
+{
+public:
+    ThreadEngineStarterBase(ThreadEngine<T> *_threadEngine)
+    : threadEngine(_threadEngine) { }
+
+    inline ThreadEngineStarterBase(const ThreadEngineStarterBase &other)
+    : threadEngine(other.threadEngine) { }
+
+    QFuture<T> startAsynchronously()
+    {
+        return threadEngine->startAsynchronously();
+    }
+
+    operator QFuture<T>()
+    {
+        return startAsynchronously();
+    }
+
+protected:
+    ThreadEngine<T> *threadEngine;
+};
+
+
+// We need to factor out the code that dereferences the T pointer,
+// with a specialization where T is void. (code that dereferences a void *
+// won't compile)
+template <typename T>
+class ThreadEngineStarter : public ThreadEngineStarterBase<T>
+{
+    typedef ThreadEngineStarterBase<T> Base;
+    typedef ThreadEngine<T> TypedThreadEngine;
+public:
+    ThreadEngineStarter(TypedThreadEngine *eng)
+        : Base(eng) { }
+
+    T startBlocking()
+    {
+        T t = *this->threadEngine->startBlocking();
+        delete this->threadEngine;
+        return t;
+    }
+};
+
+// Full template specialization where T is void.
+template <>
+class ThreadEngineStarter<void> : public ThreadEngineStarterBase<void>
+{
+public:
+    ThreadEngineStarter<void>(ThreadEngine<void> *_threadEngine)
+    :ThreadEngineStarterBase<void>(_threadEngine) {}
+
+    void startBlocking()
+    {
+        this->threadEngine->startBlocking();
+        delete this->threadEngine;
+    }
+};
+
+template <typename ThreadEngine>
+inline ThreadEngineStarter<typename ThreadEngine::ResultType> startThreadEngine(ThreadEngine *threadEngine)
+{
+    return ThreadEngineStarter<typename ThreadEngine::ResultType>(threadEngine);
+}
+
+} // namespace QtConcurrent
+
+#endif //qdoc
+
+QT_END_NAMESPACE
+QT_END_HEADER
+
+#endif // QT_NO_CONCURRENT
+
+#endif