[556] | 1 | /****************************************************************************
|
---|
| 2 | **
|
---|
[651] | 3 | ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
|
---|
[556] | 4 | ** All rights reserved.
|
---|
| 5 | ** Contact: Nokia Corporation ([email protected])
|
---|
| 6 | **
|
---|
| 7 | ** This file is part of the documentation of the Qt Toolkit.
|
---|
| 8 | **
|
---|
| 9 | ** $QT_BEGIN_LICENSE:LGPL$
|
---|
| 10 | ** Commercial Usage
|
---|
| 11 | ** Licensees holding valid Qt Commercial licenses may use this file in
|
---|
| 12 | ** accordance with the Qt Commercial License Agreement provided with the
|
---|
| 13 | ** Software or, alternatively, in accordance with the terms contained in
|
---|
| 14 | ** a written agreement between you and Nokia.
|
---|
| 15 | **
|
---|
| 16 | ** GNU Lesser General Public License Usage
|
---|
| 17 | ** Alternatively, this file may be used under the terms of the GNU Lesser
|
---|
| 18 | ** General Public License version 2.1 as published by the Free Software
|
---|
| 19 | ** Foundation and appearing in the file LICENSE.LGPL included in the
|
---|
| 20 | ** packaging of this file. Please review the following information to
|
---|
| 21 | ** ensure the GNU Lesser General Public License version 2.1 requirements
|
---|
| 22 | ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
|
---|
| 23 | **
|
---|
| 24 | ** In addition, as a special exception, Nokia gives you certain additional
|
---|
| 25 | ** rights. These rights are described in the Nokia Qt LGPL Exception
|
---|
| 26 | ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
|
---|
| 27 | **
|
---|
| 28 | ** GNU General Public License Usage
|
---|
| 29 | ** Alternatively, this file may be used under the terms of the GNU
|
---|
| 30 | ** General Public License version 3.0 as published by the Free Software
|
---|
| 31 | ** Foundation and appearing in the file LICENSE.GPL included in the
|
---|
| 32 | ** packaging of this file. Please review the following information to
|
---|
| 33 | ** ensure the GNU General Public License version 3.0 requirements will be
|
---|
| 34 | ** met: http://www.gnu.org/copyleft/gpl.html.
|
---|
| 35 | **
|
---|
| 36 | ** If you have questions regarding the use of this file, please contact
|
---|
| 37 | ** Nokia at [email protected].
|
---|
| 38 | ** $QT_END_LICENSE$
|
---|
| 39 | **
|
---|
| 40 | ****************************************************************************/
|
---|
| 41 |
|
---|
| 42 | /*!
|
---|
| 43 | \page unix-signals.html
|
---|
| 44 | \title Calling Qt Functions From Unix Signal Handlers
|
---|
| 45 | \brief You can't. But don't despair, there is a way...
|
---|
| 46 |
|
---|
| 47 | \ingroup platform-specific
|
---|
| 48 | \ingroup best-practices
|
---|
| 49 |
|
---|
| 50 | You \e can't call Qt functions from Unix signal handlers. The
|
---|
| 51 | standard POSIX rule applies: You can only call async-signal-safe
|
---|
| 52 | functions from signal handlers. See \l
|
---|
| 53 | {http://www.opengroup.org/onlinepubs/000095399/functions/xsh_chap02_04.html#tag_02_04_01}
|
---|
| 54 | {Signal Actions} for the complete list of functions you can call
|
---|
| 55 | from Unix signal handlers.
|
---|
| 56 |
|
---|
| 57 | But don't despair, there is a way to use Unix signal handlers with
|
---|
| 58 | Qt. The strategy is to have your Unix signal handler do something
|
---|
| 59 | that will eventually cause a Qt signal to be emitted, and then you
|
---|
| 60 | simply return from your Unix signal handler. Back in your Qt
|
---|
| 61 | program, that Qt signal gets emitted and then received by your Qt
|
---|
| 62 | slot function, where you can safely do whatever Qt stuff you
|
---|
| 63 | weren't allowed to do in the Unix signal handler.
|
---|
| 64 |
|
---|
| 65 | One simple way to make this happen is to declare a socket pair in
|
---|
| 66 | your class for each Unix signal you want to handle. The socket
|
---|
| 67 | pairs are declared as static data members. You also create a
|
---|
| 68 | QSocketNotifier to monitor the \e read end of each socket pair,
|
---|
| 69 | declare your Unix signal handlers to be static class methods, and
|
---|
| 70 | declare a slot function corresponding to each of your Unix signal
|
---|
| 71 | handlers. In this example, we intend to handle both the SIGHUP and
|
---|
| 72 | SIGTERM signals. Note: You should read the socketpair(2) and the
|
---|
| 73 | sigaction(2) man pages before plowing through the following code
|
---|
| 74 | snippets.
|
---|
| 75 |
|
---|
| 76 | \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 0
|
---|
| 77 |
|
---|
| 78 | In the MyDaemon constructor, use the socketpair(2) function to
|
---|
| 79 | initialize each file descriptor pair, and then create the
|
---|
| 80 | QSocketNotifier to monitor the \e read end of each pair. The
|
---|
| 81 | activated() signal of each QSocketNotifier is connected to the
|
---|
| 82 | appropriate slot function, which effectively converts the Unix
|
---|
| 83 | signal to the QSocketNotifier::activated() signal.
|
---|
| 84 |
|
---|
| 85 | \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 1
|
---|
| 86 |
|
---|
| 87 | Somewhere else in your startup code, you install your Unix signal
|
---|
| 88 | handlers with sigaction(2).
|
---|
| 89 |
|
---|
| 90 | \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 2
|
---|
| 91 |
|
---|
| 92 | In your Unix signal handlers, you write a byte to the \e write end
|
---|
| 93 | of a socket pair and return. This will cause the corresponding
|
---|
| 94 | QSocketNotifier to emit its activated() signal, which will in turn
|
---|
| 95 | cause the appropriate Qt slott function to run.
|
---|
| 96 |
|
---|
| 97 | \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 3
|
---|
| 98 |
|
---|
| 99 | In the slot functions connected to the
|
---|
| 100 | QSocketNotifier::activated() signals, you \e read the byte. Now
|
---|
| 101 | you are safely back in Qt with your signal, and you can do all the
|
---|
| 102 | Qt stuff you weren'tr allowed to do in the Unix signal handler.
|
---|
| 103 |
|
---|
| 104 | \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 4
|
---|
| 105 | */
|
---|