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/****************************************************************************
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**
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** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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** All rights reserved.
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** Contact: Nokia Corporation (qt-info@nokia.com)
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**
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** This file is part of the examples of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** No Commercial Usage
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** This file contains pre-release code and may not be distributed.
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** You may use this file in accordance with the terms and conditions
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** contained in the Technology Preview License Agreement accompanying
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** this package.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 2.1 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Nokia gives you certain additional
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** rights. These rights are described in the Nokia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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** If you have questions regarding the use of this file, please contact
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** Nokia at qt-info@nokia.com.
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**
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**
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**
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**
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**
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**
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#include "dialog.h"
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#include <QFileDialog>
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#include <QBuffer>
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#include <QtCore/QDebug>
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/*!
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\class Dialog
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\brief This class is a simple example of how to use QSharedMemory.
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It is a simple dialog that presents a few buttons. To compile the
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example, run make in qt/examples/ipc. Then run the executable twice
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to create two processes running the dialog. In one of the processes,
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press the button to load an image into a shared memory segment, and
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then select an image file to load. Once the first process has loaded
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and displayed the image, in the second process, press the button to
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read the same image from shared memory. The second process displays
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the same image loaded from its new loaction in shared memory.
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*/
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/*!
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The class contains a data member \l {QSharedMemory} {sharedMemory},
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which is initialized with the key "QSharedMemoryExample" to force
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all instances of Dialog to access the same shared memory segment.
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The constructor also connects the clicked() signal from each of the
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three dialog buttons to the slot function appropriate for handling
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each button.
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*/
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//! [0]
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Dialog::Dialog(QWidget *parent)
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: QDialog(parent), sharedMemory("QSharedMemoryExample")
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{
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ui.setupUi(this);
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connect(ui.loadFromFileButton, SIGNAL(clicked()), SLOT(loadFromFile()));
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connect(ui.loadFromSharedMemoryButton,
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SIGNAL(clicked()),
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SLOT(loadFromMemory()));
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setWindowTitle(tr("SharedMemory Example"));
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}
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//! [0]
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/*!
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This slot function is called when the \tt {Load Image From File...}
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button is pressed on the firs Dialog process. First, it tests
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whether the process is already connected to a shared memory segment
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and, if so, detaches from that segment. This ensures that we always
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start the example from the beginning if we run it multiple times
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with the same two Dialog processes. After detaching from an existing
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shared memory segment, the user is prompted to select an image file.
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The selected file is loaded into a QImage. The QImage is displayed
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in the Dialog and streamed into a QBuffer with a QDataStream.
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Next, it gets a new shared memory segment from the system big enough
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to hold the image data in the QBuffer, and it locks the segment to
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prevent the second Dialog process from accessing it. Then it copies
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the image from the QBuffer into the shared memory segment. Finally,
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it unlocks the shared memory segment so the second Dialog process
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can access it.
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After this function runs, the user is expected to press the \tt
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{Load Image from Shared Memory} button on the second Dialog process.
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\sa loadFromMemory()
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*/
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//! [1]
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void Dialog::loadFromFile()
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{
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if (sharedMemory.isAttached())
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detach();
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ui.label->setText(tr("Select an image file"));
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QString fileName = QFileDialog::getOpenFileName(0, QString(), QString(),
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tr("Images (*.png *.xpm *.jpg)"));
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QImage image;
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if (!image.load(fileName)) {
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ui.label->setText(tr("Selected file is not an image, please select another."));
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return;
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}
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ui.label->setPixmap(QPixmap::fromImage(image));
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//! [1] //! [2]
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// load into shared memory
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QBuffer buffer;
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buffer.open(QBuffer::ReadWrite);
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QDataStream out(&buffer);
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out << image;
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int size = buffer.size();
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if (!sharedMemory.create(size)) {
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ui.label->setText(tr("Unable to create shared memory segment."));
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return;
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}
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sharedMemory.lock();
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char *to = (char*)sharedMemory.data();
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const char *from = buffer.data().data();
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memcpy(to, from, qMin(sharedMemory.size(), size));
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sharedMemory.unlock();
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}
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//! [2]
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/*!
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This slot function is called in the second Dialog process, when the
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user presses the \tt {Load Image from Shared Memory} button. First,
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it attaches the process to the shared memory segment created by the
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first Dialog process. Then it locks the segment for exclusive
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access, copies the image data from the segment into a QBuffer, and
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streams the QBuffer into a QImage. Then it unlocks the shared memory
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segment, detaches from it, and finally displays the QImage in the
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Dialog.
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\sa loadFromFile()
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*/
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//! [3]
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void Dialog::loadFromMemory()
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{
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if (!sharedMemory.attach()) {
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ui.label->setText(tr("Unable to attach to shared memory segment.\n" \
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"Load an image first."));
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return;
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}
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QBuffer buffer;
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QDataStream in(&buffer);
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QImage image;
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sharedMemory.lock();
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buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
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buffer.open(QBuffer::ReadOnly);
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in >> image;
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sharedMemory.unlock();
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sharedMemory.detach();
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ui.label->setPixmap(QPixmap::fromImage(image));
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}
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//! [3]
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/*!
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This private function is called by the destructor to detach the
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process from its shared memory segment. When the last process
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detaches from a shared memory segment, the system releases the
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shared memory.
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*/
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void Dialog::detach()
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{
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if (!sharedMemory.detach())
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ui.label->setText(tr("Unable to detach from shared memory."));
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}
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