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qd_messenger.h

//C-  -*- C++ -*-
//C- -------------------------------------------------------------------
//C- DjVuLibre-3.5
//C- Copyright (c) 2002  Leon Bottou and Yann Le Cun.
//C- Copyright (c) 2001  AT&T
//C-
//C- This software is subject to, and may be distributed under, the
//C- GNU General Public License, either Version 2 of the license,
//C- or (at your option) any later version. The license should have
//C- accompanied the software or you may obtain a copy of the license
//C- from the Free Software Foundation at http://www.fsf.org .
//C-
//C- This program is distributed in the hope that it will be useful,
//C- but WITHOUT ANY WARRANTY; without even the implied warranty of
//C- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//C- GNU General Public License for more details.
//C- 
//C- DjVuLibre-3.5 is derived from the DjVu(r) Reference Library from
//C- Lizardtech Software.  Lizardtech Software has authorized us to
//C- replace the original DjVu(r) Reference Library notice by the following
//C- text (see doc/lizard2002.djvu and doc/lizardtech2007.djvu):
//C-
//C-  ------------------------------------------------------------------
//C- | DjVu (r) Reference Library (v. 3.5)
//C- | Copyright (c) 1999-2001 LizardTech, Inc. All Rights Reserved.
//C- | The DjVu Reference Library is protected by U.S. Pat. No.
//C- | 6,058,214 and patents pending.
//C- |
//C- | This software is subject to, and may be distributed under, the
//C- | GNU General Public License, either Version 2 of the license,
//C- | or (at your option) any later version. The license should have
//C- | accompanied the software or you may obtain a copy of the license
//C- | from the Free Software Foundation at http://www.fsf.org .
//C- |
//C- | The computer code originally released by LizardTech under this
//C- | license and unmodified by other parties is deemed "the LIZARDTECH
//C- | ORIGINAL CODE."  Subject to any third party intellectual property
//C- | claims, LizardTech grants recipient a worldwide, royalty-free, 
//C- | non-exclusive license to make, use, sell, or otherwise dispose of 
//C- | the LIZARDTECH ORIGINAL CODE or of programs derived from the 
//C- | LIZARDTECH ORIGINAL CODE in compliance with the terms of the GNU 
//C- | General Public License.   This grant only confers the right to 
//C- | infringe patent claims underlying the LIZARDTECH ORIGINAL CODE to 
//C- | the extent such infringement is reasonably necessary to enable 
//C- | recipient to make, have made, practice, sell, or otherwise dispose 
//C- | of the LIZARDTECH ORIGINAL CODE (or portions thereof) and not to 
//C- | any greater extent that may be necessary to utilize further 
//C- | modifications or combinations.
//C- |
//C- | The LIZARDTECH ORIGINAL CODE is provided "AS IS" WITHOUT WARRANTY
//C- | OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
//C- | TO ANY WARRANTY OF NON-INFRINGEMENT, OR ANY IMPLIED WARRANTY OF
//C- | MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
//C- +------------------------------------------------------------------
// 
// $Id: qd_messenger.h,v 1.7 2007/03/25 20:48:25 leonb Exp $
// $Name: release_3_5_21 $

#ifndef HDR_QD_MESSENGER
#define HDR_QD_MESSENGER
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#if NEED_GNUG_PRAGMAS
# pragma interface
#endif


#include "GThreads.h"
#include "GContainer.h"
#include "debug.h"
#include "GURL.h"

#include <qobject.h>

// This class actually does synchronization between two threads by maintaining
// a pipe and queue of messages. There can be just one queue per application
// QDMessenger will be able to use the same queue as they provide their
// address in every queue message so that the QDMessageQueue knows whom
// to direct a message to.
//
// In some cases it's necessary to look ahead in the queue for other events
// for the same QDMessenger. Here is an explanation "why":
//
// "It's important to do so at least for REDRAW events since usually
// Decoder works pretty fast and manages to decode everything by the
// moment when visualizer finishes redrawing the B&W picture. While
// decoding the decoder sends a bunch of REDRAW requests thru this
// messenger. Unfortunately, if we process it one-by-one then no event
// compression will be observed as QT seems to pay much more attention
// to XEvents (generated by x11Redraw) than to active SocketNotifiers.
// Thus, instead of processing another pipe REDRAW command (and thus
// sending another Expose event, which could be merged with the previous
// one), QT notices Expose events returned from XServer and processes
// it immediately. So we don't let QT return to event loop and do it.
// We process all pending commands at once"
//
// So, there is a "look_ahead" setting for every QDMessenger, that the queue
// may deal with. Every time when smth is read from the pipe, the queue
// senses the QDMessenger which should take the message and, if look_ahead
// is TRUE, it will look thru the queue for other messages for the same
// QDMessenger until all of them are processed.

class QDMessageQueue : public QObject
{
   Q_OBJECT
public:
   class Item
   {
   public:
      Item  * next;

      class QDMessenger * messenger;
      int   cmd;
      int   req;
      GUTF8String title, msg;
      GUTF8String url, target;

      Item(class QDMessenger * _messenger, int _cmd) :
          next(0), messenger(_messenger), cmd(_cmd) {};
   };
private:
   int                  fd[2];
   GCriticalSection     queue_lock;
   Item                 * queue_head;
private slots:
   void           notifierActivated(int);
public:
   void           addQueueItem(Item * item);
   void           doOneQueueItem(void);
   void           clearMessenger(class QDMessenger * messenger);

   QDMessageQueue(QObject * parent=0, const char * name=0);
   virtual ~QDMessageQueue(void);
};

class QDMessenger : public QObject
{
   Q_OBJECT
private:
      // CMD_LAYOUT and CMD_REDRAW could have been implemented via
      // CMD_GENERAL_REQ as they don't require any arguments, but it's
      // nice to have these requests in separate
   enum CMD { SHOW_STATUS=0, LAYOUT, REDRAW,
            SHOW_ERROR, GET_URL, GENERAL_REQ, GENERAL_MSG };

   static QDMessageQueue      * queue;
   bool           look_ahead;
signals:
   void           sigRedraw(void);
   void           sigLayout(void);
   void           sigShowError(const GUTF8String &, const GUTF8String &);
   void           sigShowStatus(const QString &);
   void           sigGetURL(const GURL & url, const GUTF8String &target);
   void           sigGeneralReq(int);
   void           sigGeneralMsg(const GUTF8String &);
public:
   void           showStatus(const QString &status);
   void           layout(void);
   void           redraw(void);
   void           showError(const GUTF8String &title, const GUTF8String &msg);
   void           getURL(const GURL & url, const GUTF8String &target);
   void           generalReq(int req);
   void           generalMsg(const GUTF8String &msg);

      // Internal: called from QDMessageQueue::notifierActivated()
   void           sendSignal(QDMessageQueue::Item * item);

   void           setLookAhead(bool la) { look_ahead=la; }
   bool           getLookAhead(void) const { return look_ahead; }
   
      // The reason to pass parent here is to provide automatic destruction
      // of the messenger when parent passes away.
      // You may safely pass parent=0 if you don't forget to destroy the
      // messenger yourself
   QDMessenger(QWidget * parent=0, const char * name=0);
   ~QDMessenger(void);
};

#endif

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