1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
|
/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** 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 either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at http://qt.nokia.com/contact.
** $QT_END_LICENSE$
**
****************************************************************************/
#include "dialog.h"
#include <QFileDialog>
#include <QBuffer>
#include <QtCore/QDebug>
/*!
\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, SIGNAL(clicked()), SLOT(loadFromFile()));
connect(ui.loadFromSharedMemoryButton,
SIGNAL(clicked()),
SLOT(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)) {
ui.label->setText(tr("Unable to create shared memory segment."));
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."));
}
|
