xiaoningsdiary/include/MediaPlayer/playlistchildthreadstracker.h

/*  Copyright (C) 2009 Väinö Lappi <djap84@gmail.com>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/

/*
 * Keeps count on child threads created for playlist to add/remove files.
 * Implements API to check if there are still threads running and stopping all threads.
 * Takes care of deleting when thread finishes it's task.
 * 
 * Originally planned to use simple system of signals/slots to get the same behaviour
 * but there was some problems (upon closing the program
 * the signals seemed never reach the destination and the program froze)
 * so I had to do this litle more complicated tracker system of Mutexes, destruction queue
 * and destructor thread to avoid using signals as much as possible.
 */

#ifndef PLAYLISTCHILDTHREADSTRACKER_H
#define PLAYLISTCHILDTHREADSTRACKER_H
//
#include <QThread>
#include <QMutex>
#include <QWaitCondition>       //Used to put thread to sleep for a while when it's not needed

class PlaylistFolderAdder;
class PlaylistEditorDialog;
class PlaylistModifierBase;

/*
 * Store child pointers here when they announce their
 * attempt to quit.
 */
struct childDestructQueueEntry
{
        PlaylistModifierBase* childPtr;
        childDestructQueueEntry* next;
};
//
class PlaylistChildThreadsTracker : public QThread
{
Q_OBJECT
public:
        PlaylistChildThreadsTracker(PlaylistEditorDialog* parent);

        /* 
         * Childs can use this announce when they are about to exit,
         * When a child calls this, it's pointer will be added to destruction
         * queue where it will be picked as soon as all childs before it have
         * been deleted. This will be done in tracker threads main event loop
         * that will after picking the child from Queue wait the child from exit
         * and then delete the child and the Queue entry.
         */
        void ChildAboutToExit(PlaylistModifierBase* childPtr);
        
        /* 
         * Add a new child thread to tracker.
         * This will only increase the child counter. The pointers are not stored
         * Since each child will send it when about to exit. Termination of child
         * is done by emitting terminateThreads(), which is connected to every child upon creation.
         */
        void AddChild();
        // Stop all childs
        void TerminateAllChilds();
        // Wait untill there's no child threads left
        void WaitChildsExit();
        // Stop this thread and wait untill exit
        void StopAndWaitExit();
protected:
        //Trackers main event loop
        void run();
private:
        PlaylistEditorDialog* iParent;
        unsigned iChildThreadCount;
        QMutex iChildThreadCounterMux;  //UI or some of the threads might collide when increasing/decreasing this counter.
        
        //The que will be modified from more than 2 threads
        QMutex iChildDestructQueueMutex;
        childDestructQueueEntry* iChildDestructQueueIndex;
        //Delay for main event loop of tracker thread when nothing to do
        QWaitCondition iTrackerMainLoopDelay;
        //locking this will cause the main event loop of tracker to exit
        QMutex iEndThread;
        QWaitCondition iWaitChildsToExitDelay;
        QWaitCondition iWaitSelfToExitDelay;
        QMutex iWaitSelfToExitMux;
signals:
        void terminateThreads();        //Use this to terminate all child threads
};
#endif

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