qt 6.5.1 original

examples/corelib/ipc/sharedmemory/CMakeLists.txt

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+# 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

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+// 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

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+// 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

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+<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

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+// 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

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+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