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 /* ============================================================
  *
  * This file is a part of digiKam project
  * https://www.digikam.org
  *
  * Date        : 2010-04-06
  * Description : Multithreaded worker object
  *
  * SPDX-FileCopyrightText: 2010-2012 by Marcel Wiesweg <marcel dot wiesweg at gmx dot de>
  * SPDX-FileCopyrightText: 2012-2024 by Gilles Caulier <caulier dot gilles at gmail dot com>
  *
  * SPDX-License-Identifier: GPL-2.0-or-later
  *
  * ============================================================ */
 
 #ifndef DIGIKAM_WORKER_OBJECT_H
 #define DIGIKAM_WORKER_OBJECT_H
 
 // Qt includes
 
 #include <QObject>
 #include <QThread>
 
 // Local includes
 
 #include "digikam_export.h"
 
 class QEventLoop;
 
 namespace Digikam
 {
 
 class WorkerObjectRunnable;
 
 class DIGIKAM_EXPORT WorkerObject : public QObject
 {
     Q_OBJECT
 
 public:
 
     enum State
     {
         Inactive,
         Scheduled,
         Running,
         Deactivating
     };
 
     enum DeactivatingMode
     {
         FlushSignals,               ///< Already sent signals are cleared
         KeepSignals,                ///< The thread is stopped, but already sent signals remain in the queue
         PhaseOut                    ///< The thread is stopped when all signals emitted until now have been processed
     };
 
 public:
 
     /**
      * Deriving from a worker object allows you to execute your slots in a thread.
      * Implement any slots and connect signals just as usual.
      * Call schedule() before or when signals are emitted. The object
      * will have moved to a thread when the signals are received by the slots.
      * Call deactivate() to stop computation.
      * Note that without calling schedule(), no signal will ever be processed.
      * You can use the connectAndSchedule convenience connection to avoid
      * having to call schedule() directly.
      * Note that you cannot make this QObject the child of another QObject.
      * Please check if you need to call shutDown from your destructor (see below).
      */
     explicit WorkerObject();
     ~WorkerObject()                       override;
 
     State state()                   const;
 
     void wait();
 
     /**
      * Sets the priority for this dynamic thread.
      * Can be set anytime. If the thread is currently not running,
      * the priority will be set when it is run next time.
      * When you set QThread::InheritPriority (default), the
      * priority is not changed but inherited from the thread pool.
      */
     void setPriority(QThread::Priority priority);
     QThread::Priority priority()    const;
 
     /**
      * You must normally call schedule() to ensure that the object is active when you send
      * a signal with work data. Instead, you can use these connect() methods
      * when connecting your signal to this object, the signal that carries work data.
      * Then the object will be scheduled each time you emit the signal.
      */
     bool connectAndSchedule(const QObject* sender,
                             const char* signal,
                             const char* method,
                             Qt::ConnectionType type = Qt::AutoConnection) const;
 
     static bool connectAndSchedule(const QObject* sender,
                                    const char* signal,
                                    const WorkerObject* receiver,
                                    const char* method,
                                    Qt::ConnectionType type = Qt::AutoConnection);
 
     static bool disconnectAndSchedule(const QObject* sender,
                                       const char* signal,
                                       const WorkerObject* receiver,
                                       const char* method);
 
 public Q_SLOTS:
 
     /**
      * Starts execution of this worker object:
      * The object is moved to a thread and an event loop started,
      * so that queued signals will be received.
      */
     void schedule();
 
     /**
      * Quits execution of this worker object.
      * If mode is FlushSignals, all already emitted signals will be cleared.
      * If mode is KeepSignals, already emitted signals are not cleared and
      * will be kept in the event queue until destruction or schedule() is called.
      * If mode is PhaseOut, already emitted signals will be processed
      * and the thread quit immediately afterwards.
      */
     void deactivate(DeactivatingMode mode = FlushSignals);
 
 Q_SIGNALS:
 
     void started();
     void finished();
 
 protected:
 
     bool transitionToRunning();
     void transitionToInactive();
 
     void run();
     void setEventLoop(QEventLoop* loop);
     void addRunnable(WorkerObjectRunnable* loop);
     void removeRunnable(WorkerObjectRunnable* loop);
 
     /**
      * If you are deleting data in your destructor which is accessed from the thread,
      * do one of the following from your destructor to guarantee a safe shutdown:
      * 1) Call this method
      * 2) Call stop() and wait(), knowing that nothing will
      *    call start() anymore after this
      * 3) Be sure the thread will never be running at destruction.
      * Note: This irrevocably stops this object.
      * Note: It is not sufficient that your parent class does this.
      * Calling this method, or providing one of the above mentioned
      * equivalent guarantees, must be done by every
      * single last class in the hierarchy with an implemented destructor deleting data.
      * (the base class destructor is always called after the derived class)
      */
     void shutDown();
 
     /**
      * Called from within thread's event loop to quit processing.
      * Quit any blocking operation.
      * Immediately afterwards, the event loop will be quit.
      */
     virtual void aboutToQuitLoop();
 
     /**
      * Called from deactivate(), typically from a different
      * thread than the worker thread, possibly the UI thread.
      * You can stop any extra controlled threads here.
      * Immediately afterwards, an event will be sent to the working
      * thread which will cause the event loop to quit. (aboutToQuitLoop())
      */
     virtual void aboutToDeactivate();
 
     bool event(QEvent* e)                 override;
 
 private:
 
     friend class WorkerObjectRunnable;
     friend class ThreadManager;
 
 private:
 
     // Disable.
     WorkerObject(const WorkerObject&)            = delete;
     WorkerObject& operator=(const WorkerObject&) = delete;
     WorkerObject(QObject*)                       = delete;
 
 private:
 
     class Private;
     Private* const d;
 };
 
 } // namespace Digikam
 
 #endif // DIGIKAM_WORKER_OBJECT_H