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+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Free Documentation License
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of this
+** file.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+  \example ipc/sharedmemory
+  \title Shared Memory Example
+
+  The Shared Memory example shows how to use the QSharedMemory class
+  to implement inter-process communication using shared memory. To
+  build the example, run make. To run the example, start two instances
+  of the executable. The main() function creates an \l {QApplication}
+  {application} and an instance of our example's Dialog class. The
+  dialog is displayed and then control is passed to the application in
+  the standard way.
+
+  \snippet examples/ipc/sharedmemory/main.cpp 0
+
+  Two instances of class Dialog appear.
+
+  \image sharedmemory-example_1.png Screenshot of the Shared Memory example
+
+  Class Dialog inherits QDialog. It encapsulates the user interface
+  and an instance of QSharedMemory. It also has two public slots,
+  loadFromFile() and loadFromMemory() that correspond to the two
+  buttons on the dialog.
+
+  \snippet examples/ipc/sharedmemory/dialog.h 0
+
+  The constructor builds the user interface widgets and connects the
+  clicked() signal of each button to the corresponding slot function.
+
+  \snippet examples/ipc/sharedmemory/dialog.cpp 0
+
+  Note that "QSharedMemoryExample" is passed to the \l {QSharedMemory}
+  {QSharedMemory()} constructor to be used as the key. This will be
+  used by the system as the identifier of the underlying shared memory
+  segment.
+
+  Click the \tt {Load Image From File...} button on one of the
+  dialogs. The loadFromFile() slot is invoked. First, it tests whether
+  a shared memory segment is already attached to the process. If so,
+  that segment is detached from the process, so we can be assured of
+  starting off the example correctly.
+
+  \snippet examples/ipc/sharedmemory/dialog.cpp 1
+
+  The user is then asked to select an image file using
+  QFileDialog::getOpenFileName(). The selected file is loaded into a
+  QImage. Using a QImage lets us ensure that the selected file is a
+  valid image, and it also allows us to immediately display the image
+  in the dialog using setPixmap().
+
+  Next the image is streamed into a QBuffer using a QDataStream. This
+  gives us the size, which we then use to \l {QSharedMemory::}
+  {create()} our shared memory segment. Creating a shared memory
+  segment automatically \l {QSharedMemory::attach()} {attaches} the
+  segment to the process. Using a QBuffer here lets us get a pointer
+  to the image data, which we then use to do a memcopy() from the
+  QBuffer into the shared memory segment.
+
+  \snippet examples/ipc/sharedmemory/dialog.cpp 2
+
+  Note that we \l {QSharedMemory::} {lock()} the shared memory segment
+  before we copy into it, and we \l {QSharedMemory::} {unlock()} it
+  again immediately after the copy. This ensures we have exclusive
+  access to the shared memory segment to do our memcopy(). If some
+  other process has the segment lock, then our process will block
+  until the lock becomes available.
+
+  Note also that the function does not \l {QSharedMemory::} {detach()}
+  from the shared memory segment after the memcopy() and
+  unlock(). Recall that when the last process detaches from a shared
+  memory segment, the segment is released by the operating
+  system. Since this process only one that is attached to the shared
+  memory segment at the moment, if loadFromFile() detached from the
+  shared memory segment, the segment would be destroyed before we get
+  to the next step.
+
+  When the function returns, if the file you selected was qt.png, your
+  first dialog looks like this.
+
+  \image sharedmemory-example_2.png Screenshot of the Shared Memory example
+
+  In the second dialog, click the \tt {Display Image From Shared
+  Memory} button. The loadFromMemory() slot is invoked. It first \l
+  {QSharedMemory::attach()} {attaches} the process to the same shared
+  memory segment created by the first process. Then it \l
+  {QSharedMemory::lock()} {locks} the segment for exclusive access and
+  links a QBuffer to the image data in the shared memory segment. It
+  then streams the data into a QImage and \l {QSharedMemory::unlock()}
+  {unlocks} the segment.
+
+  \snippet examples/ipc/sharedmemory/dialog.cpp 3
+
+  In this case, the function does \l {QSharedMemory::} {detach()} from
+  the segment, because now we are effectively finished using
+  it. Finally, the QImage is displayed. At this point, both dialogs
+  should be showing the same image. When you close the first dialog,
+  the Dialog destructor calls the QSharedMemory destructor, which
+  detaches from the shared memory segment. Since this is the last
+  process to be detached from the segment, the operating system will
+  now release the shared memory.
+
+ */