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50
51#include "dialog.h"
52#include <QFileDialog>
53#include <QBuffer>
54
55/*!
56 \class Dialog
57
58 \brief This class is a simple example of how to use QSharedMemory.
59
60 It is a simple dialog that presents a few buttons. To compile the
61 example, run make in qt/examples/ipc. Then run the executable twice
62 to create two processes running the dialog. In one of the processes,
63 press the button to load an image into a shared memory segment, and
64 then select an image file to load. Once the first process has loaded
65 and displayed the image, in the second process, press the button to
66 read the same image from shared memory. The second process displays
67 the same image loaded from its new loaction in shared memory.
68*/
69
70/*!
71 The class contains a data member \l {QSharedMemory} {sharedMemory},
72 which is initialized with the key "QSharedMemoryExample" to force
73 all instances of Dialog to access the same shared memory segment.
74 The constructor also connects the clicked() signal from each of the
75 three dialog buttons to the slot function appropriate for handling
76 each button.
77*/
78//! [0]
79Dialog::Dialog(QWidget *parent)
80 : QDialog(parent), sharedMemory("QSharedMemoryExample")
81{
82 ui.setupUi(this);
83 connect(sender: ui.loadFromFileButton, signal: &QPushButton::clicked,
84 receiver: this, slot: &Dialog::loadFromFile);
85 connect(sender: ui.loadFromSharedMemoryButton, signal: &QPushButton::clicked,
86 receiver: this, slot: &Dialog::loadFromMemory);
87 setWindowTitle(tr(s: "SharedMemory Example"));
88}
89//! [0]
90
91/*!
92 This slot function is called when the \tt {Load Image From File...}
93 button is pressed on the firs Dialog process. First, it tests
94 whether the process is already connected to a shared memory segment
95 and, if so, detaches from that segment. This ensures that we always
96 start the example from the beginning if we run it multiple times
97 with the same two Dialog processes. After detaching from an existing
98 shared memory segment, the user is prompted to select an image file.
99 The selected file is loaded into a QImage. The QImage is displayed
100 in the Dialog and streamed into a QBuffer with a QDataStream.
101
102 Next, it gets a new shared memory segment from the system big enough
103 to hold the image data in the QBuffer, and it locks the segment to
104 prevent the second Dialog process from accessing it. Then it copies
105 the image from the QBuffer into the shared memory segment. Finally,
106 it unlocks the shared memory segment so the second Dialog process
107 can access it.
108
109 After this function runs, the user is expected to press the \tt
110 {Load Image from Shared Memory} button on the second Dialog process.
111
112 \sa loadFromMemory()
113 */
114//! [1]
115void Dialog::loadFromFile()
116{
117 if (sharedMemory.isAttached())
118 detach();
119
120 ui.label->setText(tr(s: "Select an image file"));
121 QString fileName = QFileDialog::getOpenFileName(parent: 0, caption: QString(), dir: QString(),
122 filter: tr(s: "Images (*.png *.xpm *.jpg)"));
123 QImage image;
124 if (!image.load(fileName)) {
125 ui.label->setText(tr(s: "Selected file is not an image, please select another."));
126 return;
127 }
128 ui.label->setPixmap(QPixmap::fromImage(image));
129//! [1] //! [2]
130
131 // load into shared memory
132 QBuffer buffer;
133 buffer.open(openMode: QBuffer::ReadWrite);
134 QDataStream out(&buffer);
135 out << image;
136 int size = buffer.size();
137
138 if (!sharedMemory.create(size)) {
139 ui.label->setText(tr(s: "Unable to create shared memory segment."));
140 return;
141 }
142 sharedMemory.lock();
143 char *to = (char*)sharedMemory.data();
144 const char *from = buffer.data().data();
145 memcpy(dest: to, src: from, n: qMin(a: sharedMemory.size(), b: size));
146 sharedMemory.unlock();
147}
148//! [2]
149
150/*!
151 This slot function is called in the second Dialog process, when the
152 user presses the \tt {Load Image from Shared Memory} button. First,
153 it attaches the process to the shared memory segment created by the
154 first Dialog process. Then it locks the segment for exclusive
155 access, copies the image data from the segment into a QBuffer, and
156 streams the QBuffer into a QImage. Then it unlocks the shared memory
157 segment, detaches from it, and finally displays the QImage in the
158 Dialog.
159
160 \sa loadFromFile()
161 */
162//! [3]
163void Dialog::loadFromMemory()
164{
165 if (!sharedMemory.attach()) {
166 ui.label->setText(tr(s: "Unable to attach to shared memory segment.\n" \
167 "Load an image first."));
168 return;
169 }
170
171 QBuffer buffer;
172 QDataStream in(&buffer);
173 QImage image;
174
175 sharedMemory.lock();
176 buffer.setData(adata: (char*)sharedMemory.constData(), alen: sharedMemory.size());
177 buffer.open(openMode: QBuffer::ReadOnly);
178 in >> image;
179 sharedMemory.unlock();
180
181 sharedMemory.detach();
182 ui.label->setPixmap(QPixmap::fromImage(image));
183}
184//! [3]
185
186/*!
187 This private function is called by the destructor to detach the
188 process from its shared memory segment. When the last process
189 detaches from a shared memory segment, the system releases the
190 shared memory.
191 */
192void Dialog::detach()
193{
194 if (!sharedMemory.detach())
195 ui.label->setText(tr(s: "Unable to detach from shared memory."));
196}
197
198

source code of qtbase/examples/corelib/ipc/sharedmemory/dialog.cpp