qt 6.5.1 original

examples/corelib/ipc/CMakeLists.txt

@@ -0,0 +1,13 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+if(NOT TARGET Qt6::Widgets)
+    return()
+endif()
+if(QT_FEATURE_sharedmemory)
+    qt_internal_add_example(sharedmemory)
+endif()
+if(QT_FEATURE_localserver AND TARGET Qt6::Network)
+    qt_internal_add_example(localfortuneserver)
+    qt_internal_add_example(localfortuneclient)
+endif()

examples/corelib/ipc/README

@@ -0,0 +1,5 @@
+These examples demonstrate IPC support in Qt.
+
+
+Documentation for these examples can be found via the Examples
+link in the main Qt documentation.

examples/corelib/ipc/doc/src/localfortuneclient.qdoc

@@ -0,0 +1,16 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example ipc/localfortuneclient
+    \title Local Fortune Client Example
+    \ingroup examples-ipc
+    \brief Demonstrates using QLocalSocket for a simple local service client.
+
+    The Local Fortune Client example shows how to create a client for a simple
+    local service using QLocalSocket. It is intended to be run alongside the
+    \l{Local Fortune Server Example}.
+
+    \image localfortuneclient-example.png Screenshot of the Local Fortune Client example
+
+*/

examples/corelib/ipc/doc/src/localfortuneserver.qdoc

@@ -0,0 +1,15 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example ipc/localfortuneserver
+    \title Local Fortune Server Example
+    \ingroup examples-ipc
+    \brief Demonstrates using QLocalServer and QLocalSocket for serving a simple local service.
+
+    The Local Fortune Server example shows how to create a server for a simple
+    local service. It is intended to be run alongside the
+    \l{Local Fortune Client Example}
+
+    \image localfortuneserver-example.png Screenshot of the Local Fortune Server example
+ */

examples/corelib/ipc/doc/src/sharedmemory.qdoc

@@ -0,0 +1,107 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+  \example ipc/sharedmemory
+  \title Shared Memory Example
+  \ingroup examples-ipc
+  \brief Demonstrates doing inter-process communication using shared memory with
+  the QSharedMemory class.
+
+  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 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 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 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 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 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 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.
+
+ */

examples/corelib/ipc/ipc.pro

@@ -0,0 +1,10 @@
+requires(qtHaveModule(widgets))
+
+TEMPLATE      = subdirs
+
+qtConfig(sharedmemory): SUBDIRS = sharedmemory
+qtHaveModule(network) {
+    QT_FOR_CONFIG += network
+
+    qtConfig(localserver): SUBDIRS += localfortuneserver localfortuneclient
+}

examples/corelib/ipc/localfortuneclient/CMakeLists.txt

@@ -0,0 +1,38 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(localfortuneclient LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/ipc/localfortuneclient")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Network Widgets)
+
+qt_standard_project_setup()
+
+qt_add_executable(localfortuneclient
+    client.cpp client.h
+    main.cpp
+)
+
+set_target_properties(localfortuneclient PROPERTIES
+    WIN32_EXECUTABLE TRUE
+    MACOSX_BUNDLE TRUE
+)
+
+target_link_libraries(localfortuneclient PRIVATE
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Network
+    Qt6::Widgets
+)
+
+install(TARGETS localfortuneclient
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/ipc/localfortuneclient/client.cpp

@@ -0,0 +1,115 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QtWidgets>
+#include <QtNetwork>
+
+#include "client.h"
+
+Client::Client(QWidget *parent)
+    : QDialog(parent),
+      hostLineEdit(new QLineEdit("fortune")),
+      getFortuneButton(new QPushButton(tr("Get Fortune"))),
+      statusLabel(new QLabel(tr("This examples requires that you run the "
+                                "Local Fortune Server example as well."))),
+      socket(new QLocalSocket(this))
+{
+    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
+    QLabel *hostLabel = new QLabel(tr("&Server name:"));
+    hostLabel->setBuddy(hostLineEdit);
+
+    statusLabel->setWordWrap(true);
+
+    getFortuneButton->setDefault(true);
+    QPushButton *quitButton = new QPushButton(tr("Quit"));
+
+    QDialogButtonBox *buttonBox = new QDialogButtonBox;
+    buttonBox->addButton(getFortuneButton, QDialogButtonBox::ActionRole);
+    buttonBox->addButton(quitButton, QDialogButtonBox::RejectRole);
+
+    in.setDevice(socket);
+    in.setVersion(QDataStream::Qt_5_10);
+
+    connect(hostLineEdit, &QLineEdit::textChanged,
+            this, &Client::enableGetFortuneButton);
+    connect(getFortuneButton, &QPushButton::clicked,
+            this, &Client::requestNewFortune);
+    connect(quitButton, &QPushButton::clicked, this, &Client::close);
+    connect(socket, &QLocalSocket::readyRead, this, &Client::readFortune);
+    connect(socket, &QLocalSocket::errorOccurred, this, &Client::displayError);
+
+    QGridLayout *mainLayout = new QGridLayout(this);
+    mainLayout->addWidget(hostLabel, 0, 0);
+    mainLayout->addWidget(hostLineEdit, 0, 1);
+    mainLayout->addWidget(statusLabel, 2, 0, 1, 2);
+    mainLayout->addWidget(buttonBox, 3, 0, 1, 2);
+
+    setWindowTitle(QGuiApplication::applicationDisplayName());
+    hostLineEdit->setFocus();
+}
+
+void Client::requestNewFortune()
+{
+    getFortuneButton->setEnabled(false);
+    blockSize = 0;
+    socket->abort();
+    socket->connectToServer(hostLineEdit->text());
+}
+
+void Client::readFortune()
+{
+    if (blockSize == 0) {
+        // Relies on the fact that QDataStream serializes a quint32 into
+        // sizeof(quint32) bytes
+        if (socket->bytesAvailable() < (int)sizeof(quint32))
+            return;
+        in >> blockSize;
+    }
+
+    if (socket->bytesAvailable() < blockSize || in.atEnd())
+        return;
+
+    QString nextFortune;
+    in >> nextFortune;
+
+    if (nextFortune == currentFortune) {
+        QTimer::singleShot(0, this, &Client::requestNewFortune);
+        return;
+    }
+
+    currentFortune = nextFortune;
+    statusLabel->setText(currentFortune);
+    getFortuneButton->setEnabled(true);
+}
+
+void Client::displayError(QLocalSocket::LocalSocketError socketError)
+{
+    switch (socketError) {
+    case QLocalSocket::ServerNotFoundError:
+        QMessageBox::information(this, tr("Local Fortune Client"),
+                                 tr("The host was not found. Please make sure "
+                                    "that the server is running and that the "
+                                    "server name is correct."));
+        break;
+    case QLocalSocket::ConnectionRefusedError:
+        QMessageBox::information(this, tr("Local Fortune Client"),
+                                 tr("The connection was refused by the peer. "
+                                    "Make sure the fortune server is running, "
+                                    "and check that the server name "
+                                    "is correct."));
+        break;
+    case QLocalSocket::PeerClosedError:
+        break;
+    default:
+        QMessageBox::information(this, tr("Local Fortune Client"),
+                                 tr("The following error occurred: %1.")
+                                 .arg(socket->errorString()));
+    }
+
+    getFortuneButton->setEnabled(true);
+}
+
+void Client::enableGetFortuneButton()
+{
+    getFortuneButton->setEnabled(!hostLineEdit->text().isEmpty());
+}

examples/corelib/ipc/localfortuneclient/client.h

@@ -0,0 +1,42 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef CLIENT_H
+#define CLIENT_H
+
+#include <QDialog>
+#include <QDataStream>
+#include <QLocalSocket>
+
+QT_BEGIN_NAMESPACE
+class QLabel;
+class QLineEdit;
+class QPushButton;
+QT_END_NAMESPACE
+
+class Client : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit Client(QWidget *parent = nullptr);
+
+private slots:
+    void requestNewFortune();
+    void readFortune();
+    void displayError(QLocalSocket::LocalSocketError socketError);
+    void enableGetFortuneButton();
+
+private:
+    QLineEdit *hostLineEdit;
+    QPushButton *getFortuneButton;
+    QLabel *statusLabel;
+
+    QLocalSocket *socket;
+    QDataStream in;
+    quint32 blockSize;
+
+    QString currentFortune;
+};
+
+#endif

examples/corelib/ipc/localfortuneclient/localfortuneclient.pro

@@ -0,0 +1,8 @@
+HEADERS       = client.h
+SOURCES       = client.cpp \
+                main.cpp
+QT           += network widgets
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/ipc/localfortuneclient
+INSTALLS += target

examples/corelib/ipc/localfortuneclient/main.cpp

@@ -0,0 +1,15 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QApplication>
+
+#include "client.h"
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+    QGuiApplication::setApplicationDisplayName(Client::tr("Local Fortune Client"));
+    Client client;
+    client.show();
+    return app.exec();
+}

examples/corelib/ipc/localfortuneserver/CMakeLists.txt

@@ -0,0 +1,38 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(localfortuneserver LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/ipc/localfortuneserver")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Network Widgets)
+
+qt_standard_project_setup()
+
+qt_add_executable(localfortuneserver
+    main.cpp
+    server.cpp server.h
+)
+
+set_target_properties(localfortuneserver PROPERTIES
+    WIN32_EXECUTABLE TRUE
+    MACOSX_BUNDLE TRUE
+)
+
+target_link_libraries(localfortuneserver PRIVATE
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Network
+    Qt6::Widgets
+)
+
+install(TARGETS localfortuneserver
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/ipc/localfortuneserver/localfortuneserver.pro

@@ -0,0 +1,8 @@
+HEADERS       = server.h
+SOURCES       = server.cpp \
+                main.cpp
+QT           += network widgets
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/ipc/localfortuneserver
+INSTALLS += target

examples/corelib/ipc/localfortuneserver/main.cpp

@@ -0,0 +1,15 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QApplication>
+
+#include "server.h"
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+    QGuiApplication::setApplicationDisplayName(Server::tr("Local Fortune Server"));
+    Server server;
+    server.show();
+    return app.exec();
+}

examples/corelib/ipc/localfortuneserver/server.cpp

@@ -0,0 +1,70 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "server.h"
+
+#include <QtWidgets>
+#include <QtNetwork>
+
+Server::Server(QWidget *parent)
+    : QDialog(parent)
+{
+    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
+
+    server = new QLocalServer(this);
+    if (!server->listen("fortune")) {
+        QMessageBox::critical(this, tr("Local Fortune Server"),
+                              tr("Unable to start the server: %1.")
+                              .arg(server->errorString()));
+        close();
+        return;
+    }
+
+    QLabel *statusLabel = new QLabel;
+    statusLabel->setWordWrap(true);
+    statusLabel->setText(tr("The server is running.\n"
+                            "Run the Local Fortune Client example now."));
+
+    fortunes << tr("You've been leading a dog's life. Stay off the furniture.")
+             << tr("You've got to think about tomorrow.")
+             << tr("You will be surprised by a loud noise.")
+             << tr("You will feel hungry again in another hour.")
+             << tr("You might have mail.")
+             << tr("You cannot kill time without injuring eternity.")
+             << tr("Computers are not intelligent. They only think they are.");
+
+    QPushButton *quitButton = new QPushButton(tr("Quit"));
+    quitButton->setAutoDefault(false);
+    connect(quitButton, &QPushButton::clicked, this, &Server::close);
+    connect(server, &QLocalServer::newConnection, this, &Server::sendFortune);
+
+    QHBoxLayout *buttonLayout = new QHBoxLayout;
+    buttonLayout->addStretch(1);
+    buttonLayout->addWidget(quitButton);
+    buttonLayout->addStretch(1);
+
+    QVBoxLayout *mainLayout = new QVBoxLayout(this);
+    mainLayout->addWidget(statusLabel);
+    mainLayout->addLayout(buttonLayout);
+
+    setWindowTitle(QGuiApplication::applicationDisplayName());
+}
+
+void Server::sendFortune()
+{
+    QByteArray block;
+    QDataStream out(&block, QIODevice::WriteOnly);
+    out.setVersion(QDataStream::Qt_5_10);
+    const int fortuneIndex = QRandomGenerator::global()->bounded(0, fortunes.size());
+    const QString &message = fortunes.at(fortuneIndex);
+    out << quint32(message.size());
+    out << message;
+
+    QLocalSocket *clientConnection = server->nextPendingConnection();
+    connect(clientConnection, &QLocalSocket::disconnected,
+            clientConnection, &QLocalSocket::deleteLater);
+
+    clientConnection->write(block);
+    clientConnection->flush();
+    clientConnection->disconnectFromServer();
+}

examples/corelib/ipc/localfortuneserver/server.h

@@ -0,0 +1,30 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef SERVER_H
+#define SERVER_H
+
+#include <QDialog>
+
+QT_BEGIN_NAMESPACE
+class QLabel;
+class QPushButton;
+class QLocalServer;
+QT_END_NAMESPACE
+
+class Server : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit Server(QWidget *parent = nullptr);
+
+private slots:
+    void sendFortune();
+
+private:
+    QLocalServer *server;
+    QStringList fortunes;
+};
+
+#endif

examples/corelib/ipc/sharedmemory/CMakeLists.txt

@@ -0,0 +1,37 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(sharedmemory LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/ipc/sharedmemory")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
+
+qt_standard_project_setup()
+
+qt_add_executable(sharedmemory
+    dialog.cpp dialog.h dialog.ui
+    main.cpp
+)
+
+set_target_properties(sharedmemory PROPERTIES
+    WIN32_EXECUTABLE TRUE
+    MACOSX_BUNDLE TRUE
+)
+
+target_link_libraries(sharedmemory PRIVATE
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Widgets
+)
+
+install(TARGETS sharedmemory
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/ipc/sharedmemory/dialog.cpp

@@ -0,0 +1,155 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "dialog.h"
+#include <QFileDialog>
+#include <QBuffer>
+
+/*!
+  \class Dialog
+
+  \brief This class is a simple example of how to use QSharedMemory.
+
+  It is a simple dialog that presents a few buttons. To compile the
+  example, run make in qt/examples/ipc. Then run the executable twice
+  to create two processes running the dialog. In one of the processes,
+  press the button to load an image into a shared memory segment, and
+  then select an image file to load. Once the first process has loaded
+  and displayed the image, in the second process, press the button to
+  read the same image from shared memory. The second process displays
+  the same image loaded from its new loaction in shared memory.
+*/
+
+/*!
+  The class contains a data member \l {QSharedMemory} {sharedMemory},
+  which is initialized with the key "QSharedMemoryExample" to force
+  all instances of Dialog to access the same shared memory segment.
+  The constructor also connects the clicked() signal from each of the
+  three dialog buttons to the slot function appropriate for handling
+  each button.
+*/
+//! [0]
+Dialog::Dialog(QWidget *parent)
+  : QDialog(parent), sharedMemory("QSharedMemoryExample")
+{
+    ui.setupUi(this);
+    connect(ui.loadFromFileButton, &QPushButton::clicked,
+            this, &Dialog::loadFromFile);
+    connect(ui.loadFromSharedMemoryButton, &QPushButton::clicked,
+            this, &Dialog::loadFromMemory);
+    setWindowTitle(tr("SharedMemory Example"));
+}
+//! [0]
+
+/*!
+  This slot function is called when the \tt {Load Image From File...}
+  button is pressed on the firs Dialog process. First, it tests
+  whether the process is already connected to a shared memory segment
+  and, if so, detaches from that segment. This ensures that we always
+  start the example from the beginning if we run it multiple times
+  with the same two Dialog processes. After detaching from an existing
+  shared memory segment, the user is prompted to select an image file.
+  The selected file is loaded into a QImage. The QImage is displayed
+  in the Dialog and streamed into a QBuffer with a QDataStream.
+
+  Next, it gets a new shared memory segment from the system big enough
+  to hold the image data in the QBuffer, and it locks the segment to
+  prevent the second Dialog process from accessing it. Then it copies
+  the image from the QBuffer into the shared memory segment. Finally,
+  it unlocks the shared memory segment so the second Dialog process
+  can access it.
+
+  After this function runs, the user is expected to press the \tt
+  {Load Image from Shared Memory} button on the second Dialog process.
+
+  \sa loadFromMemory()
+ */
+//! [1]
+void Dialog::loadFromFile()
+{
+    if (sharedMemory.isAttached())
+        detach();
+
+    ui.label->setText(tr("Select an image file"));
+    QString fileName = QFileDialog::getOpenFileName(0, QString(), QString(),
+                                        tr("Images (*.png *.xpm *.jpg)"));
+    QImage image;
+    if (!image.load(fileName)) {
+        ui.label->setText(tr("Selected file is not an image, please select another."));
+        return;
+    }
+    ui.label->setPixmap(QPixmap::fromImage(image));
+//! [1] //! [2]
+
+    // load into shared memory
+    QBuffer buffer;
+    buffer.open(QBuffer::ReadWrite);
+    QDataStream out(&buffer);
+    out << image;
+    int size = buffer.size();
+
+    if (!sharedMemory.create(size)) {
+        if (sharedMemory.error() == QSharedMemory::AlreadyExists) {
+            sharedMemory.attach();
+        } else {
+            ui.label->setText(tr("Unable to create or attach to shared memory segment: %1")
+                                .arg(sharedMemory.errorString()));
+            return;
+        }
+    }
+    sharedMemory.lock();
+    char *to = (char*)sharedMemory.data();
+    const char *from = buffer.data().data();
+    memcpy(to, from, qMin(sharedMemory.size(), size));
+    sharedMemory.unlock();
+}
+//! [2]
+
+/*!
+  This slot function is called in the second Dialog process, when the
+  user presses the \tt {Load Image from Shared Memory} button. First,
+  it attaches the process to the shared memory segment created by the
+  first Dialog process. Then it locks the segment for exclusive
+  access, copies the image data from the segment into a QBuffer, and
+  streams the QBuffer into a QImage. Then it unlocks the shared memory
+  segment, detaches from it, and finally displays the QImage in the
+  Dialog.
+
+  \sa loadFromFile()
+ */
+//! [3]
+void Dialog::loadFromMemory()
+{
+    if (!sharedMemory.attach()) {
+        ui.label->setText(tr("Unable to attach to shared memory segment.\n" \
+                             "Load an image first."));
+        return;
+    }
+
+    QBuffer buffer;
+    QDataStream in(&buffer);
+    QImage image;
+
+    sharedMemory.lock();
+    buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
+    buffer.open(QBuffer::ReadOnly);
+    in >> image;
+    sharedMemory.unlock();
+
+    sharedMemory.detach();
+    ui.label->setPixmap(QPixmap::fromImage(image));
+}
+//! [3]
+
+/*!
+  This private function is called by the destructor to detach the
+  process from its shared memory segment. When the last process
+  detaches from a shared memory segment, the system releases the
+  shared memory.
+ */
+void Dialog::detach()
+{
+    if (!sharedMemory.detach())
+        ui.label->setText(tr("Unable to detach from shared memory."));
+}
+

examples/corelib/ipc/sharedmemory/dialog.h

@@ -0,0 +1,33 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef DIALOG_H
+#define DIALOG_H
+
+#include <QDialog>
+#include <QSharedMemory>
+#include "ui_dialog.h"
+
+//! [0]
+class Dialog : public QDialog
+{
+    Q_OBJECT
+
+  public:
+    Dialog(QWidget *parent = nullptr);
+
+  public slots:
+    void loadFromFile();
+    void loadFromMemory();
+
+ private:
+    void detach();
+
+  private:
+    Ui::Dialog ui;
+    QSharedMemory sharedMemory;
+};
+//! [0]
+
+#endif
+

examples/corelib/ipc/sharedmemory/dialog.ui

@@ -0,0 +1,47 @@
+<ui version="4.0" >
+ <class>Dialog</class>
+ <widget class="QDialog" name="Dialog" >
+  <property name="geometry" >
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>451</width>
+    <height>322</height>
+   </rect>
+  </property>
+  <property name="windowTitle" >
+   <string>Dialog</string>
+  </property>
+  <layout class="QGridLayout" >
+   <item row="0" column="0" >
+    <widget class="QPushButton" name="loadFromFileButton" >
+     <property name="text" >
+      <string>Load Image From File...</string>
+     </property>
+    </widget>
+   </item>
+   <item row="1" column="0" >
+    <widget class="QLabel" name="label" >
+     <property name="text" >
+      <string>Launch two of these dialogs.  In the first, press the top button and load an image from a file.  In the second, press the bottom button and display the loaded image from shared memory.</string>
+     </property>
+     <property name="alignment" >
+      <set>Qt::AlignCenter</set>
+     </property>
+     <property name="wordWrap" >
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
+   <item row="2" column="0" >
+    <widget class="QPushButton" name="loadFromSharedMemoryButton" >
+     <property name="text" >
+      <string>Display Image From Shared Memory</string>
+     </property>
+    </widget>
+   </item>
+  </layout>
+ </widget>
+ <resources/>
+ <connections/>
+</ui>

examples/corelib/ipc/sharedmemory/main.cpp

@@ -0,0 +1,16 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QApplication>
+#include "dialog.h"
+
+//! [0]
+int main(int argc, char *argv[])
+{
+    QApplication application(argc, argv);
+    Dialog dialog;
+    dialog.show();
+    return application.exec();
+}
+//! [0]
+

examples/corelib/ipc/sharedmemory/sharedmemory.pro

@@ -0,0 +1,16 @@
+QT += widgets
+requires(qtConfig(filedialog))
+
+SOURCES += main.cpp \
+           dialog.cpp 
+
+HEADERS += dialog.h
+
+# Forms and resources
+FORMS += dialog.ui
+
+EXAMPLE_FILES = *.png
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/ipc/sharedmemory
+INSTALLS += target