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author | axis <qt-info@nokia.com> | 2009-04-24 11:34:15 (GMT) |
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committer | axis <qt-info@nokia.com> | 2009-04-24 11:34:15 (GMT) |
commit | 8f427b2b914d5b575a4a7c0ed65d2fb8f45acc76 (patch) | |
tree | a17e1a767a89542ab59907462206d7dcf2e504b2 /doc/src/unix-signal-handlers.qdoc | |
download | Qt-8f427b2b914d5b575a4a7c0ed65d2fb8f45acc76.zip Qt-8f427b2b914d5b575a4a7c0ed65d2fb8f45acc76.tar.gz Qt-8f427b2b914d5b575a4a7c0ed65d2fb8f45acc76.tar.bz2 |
Long live Qt for S60!
Diffstat (limited to 'doc/src/unix-signal-handlers.qdoc')
-rw-r--r-- | doc/src/unix-signal-handlers.qdoc | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/doc/src/unix-signal-handlers.qdoc b/doc/src/unix-signal-handlers.qdoc new file mode 100644 index 0000000..6efaa6f --- /dev/null +++ b/doc/src/unix-signal-handlers.qdoc @@ -0,0 +1,103 @@ +/**************************************************************************** +** +** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). +** Contact: Qt Software Information (qt-info@nokia.com) +** +** This file is part of the documentation 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 qt-sales@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \page unix-signals.html + \title Calling Qt Functions From Unix Signal Handlers + \ingroup platform-notes + \brief You can't. But don't despair, there is a way... + + You \e can't call Qt functions from Unix signal handlers. The + standard POSIX rule applies: You can only call async-signal-safe + functions from signal handlers. See \l + {http://www.opengroup.org/onlinepubs/000095399/functions/xsh_chap02_04.html#tag_02_04_01} + {Signal Actions} for the complete list of functions you can call + from Unix signal handlers. + + But don't despair, there is a way to use Unix signal handlers with + Qt. The strategy is to have your Unix signal handler do something + that will eventually cause a Qt signal to be emitted, and then you + simply return from your Unix signal handler. Back in your Qt + program, that Qt signal gets emitted and then received by your Qt + slot function, where you can safely do whatever Qt stuff you + weren't allowed to do in the Unix signal handler. + + One simple way to make this happen is to declare a socket pair in + your class for each Unix signal you want to handle. The socket + pairs are declared as static data members. You also create a + QSocketNotifier to monitor the \e read end of each socket pair, + declare your Unix signal handlers to be static class methods, and + declare a slot function corresponding to each of your Unix signal + handlers. In this example, we intend to handle both the SIGHUP and + SIGTERM signals. Note: You should read the socketpair(2) and the + sigaction(2) man pages before plowing through the following code + snippets. + + \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 0 + + In the MyDaemon constructor, use the socketpair(2) function to + initialize each file descriptor pair, and then create the + QSocketNotifier to monitor the \e read end of each pair. The + activated() signal of each QSocketNotifier is connected to the + appropriate slot function, which effectively converts the Unix + signal to the QSocketNotifier::activated() signal. + + \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 1 + + Somewhere else in your startup code, you install your Unix signal + handlers with sigaction(2). + + \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 2 + + In your Unix signal handlers, you write a byte to the \e write end + of a socket pair and return. This will cause the corresponding + QSocketNotifier to emit its activated() signal, which will in turn + cause the appropriate Qt slott function to run. + + \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 3 + + In the slot functions connected to the + QSocketNotifier::activated() signals, you \e read the byte. Now + you are safely back in Qt with your signal, and you can do all the + Qt stuff you weren'tr allowed to do in the Unix signal handler. + + \snippet doc/src/snippets/code/doc_src_unix-signal-handlers.qdoc 4 +*/ |