author | Dominic Pinkman <dominic.pinkman@nokia.com> |
Tue, 20 Jul 2010 12:00:49 +0100 | |
changeset 13 | 48780e181b38 |
parent 7 | 51a74ef9ed63 |
permissions | -rw-r--r-- |
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<?xml version="1.0" encoding="utf-8"?> |
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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<!-- This component and the accompanying materials are made available under the terms of the License |
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"Eclipse Public License v1.0" which accompanies this distribution, |
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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<!-- Initial Contributors: |
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Nokia Corporation - initial contribution. |
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Contributors: |
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--> |
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<!DOCTYPE concept |
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PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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<concept id="GUID-41F33130-7968-5016-9ACE-9E9F906118DB" xml:lang="en"><title>Using POSIX |
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Signals</title><prolog><metadata><keywords/></metadata></prolog><conbody> |
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<p>A POSIX signal is a software equivalent of an interrupt. To handle a signal, |
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a signal handler (which is a function) must be registered for that signal. |
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On receipt of the signal, the operating system stops the process at its point |
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of execution and executes the signal handler. The signal handler may terminate |
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the process. If it does not, the OS resumes the process at the point it stopped. |
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For this reason signals can be used as a form of IPC within a process or between |
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two or more co-operating processes. </p> |
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<p>Signals are broadly classified into two types: </p> |
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<ul> |
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<li id="GUID-7C76E732-29E3-52C3-B757-D9755ABDE96F"><p> <b>Non-realtime signals |
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:</b> Non-realtime signals inform a process about system events. For example, <codeph>SIGINT</codeph> signifies |
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a user interrupt request (typically from a console). You can use the <codeph>SIGUSR1</codeph> and <codeph>SIGUSR2</codeph> signals |
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to define custom (user-defined) signals for your program. </p> </li> |
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<li id="GUID-30AC114F-EB7F-59C8-8E9D-03816D8E7A42"><p> <b>Real-time signals:</b> As |
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the name signifies, real-time signals inform a process about the occurrence |
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of real-time events, such as high-resolution timer expiration, explicit signal |
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delivery and asynchronous I/O completion. Real-time signals are different |
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from non-realtime signals in the following ways: </p> <ul> |
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<li id="GUID-9F352345-C466-52E2-AD82-491F7B0A8028"><p>They are delivered in |
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the order they are generated. </p> </li> |
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<li id="GUID-B386608A-1137-5ED0-B4FB-B78413ABA40E"><p>When a real-time signal |
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is delivered to a process and is blocked, first it is queued. Later, if the |
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same real-time signal is delivered to the process again, it is queued once |
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again. But for non-realtime signals, the signal is queued only once (when |
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it is blocked) regardless of the number of times it is delivered to a process. </p> </li> |
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</ul> <p>Real-time signals are in the range <codeph>SIGRTMIN</codeph> to <codeph>SIGRTMAX</codeph>. |
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You can refer to real-time signals using the notation <codeph>SIGRTMIN+n</codeph>. |
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For example, <codeph>SIGRTMIN</codeph>, <codeph>SIGRTMIN+1</codeph>, <codeph>SIGRTMIN+2</codeph>, |
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... <codeph>SIGRTMAX</codeph>. </p> </li> |
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</ul> |
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<p> <b>Note:</b> Real-time signals are subject to the same latency as non-realtime |
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signals in P.I.P.S. </p> |
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<p>The following topics describe how POSIX signals are emulated on the Symbian |
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platform. They also describe how you can use these signals when you develop |
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POSIX compliant applications or port POSIX-based applications onto the Symbian |
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platform. </p> |
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</conbody></concept> |