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+++ b/Symbian3/SDK/Source/GUID-41F33130-7968-5016-9ACE-9E9F906118DB.dita	Wed Mar 31 11:11:55 2010 +0100
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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-41F33130-7968-5016-9ACE-9E9F906118DB" xml:lang="en"><title>Using POSIX
+Signals</title><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>A POSIX signal is a software equivalent of an interrupt. To handle a signal,
+a signal handler (which is a function) must be registered for that signal.
+On receipt of the signal, the operating system stops the process at its point
+of execution and executes the signal handler. The signal handler may terminate
+the process. If it does not, the OS resumes the process at the point it stopped.
+For this reason signals can be used as a form of IPC within a process or between
+two or more co-operating processes. </p>
+<p>Signals are broadly classified into two types: </p>
+<ul>
+<li id="GUID-7C76E732-29E3-52C3-B757-D9755ABDE96F"><p> <b>Non-realtime signals
+:</b> Non-realtime signals inform a process about system events. For example, <codeph>SIGINT</codeph> signifies
+a user interrupt request (typically from a console). You can use the <codeph>SIGUSR1</codeph> and <codeph>SIGUSR2</codeph> signals
+to define custom (user-defined) signals for your program. </p> </li>
+<li id="GUID-30AC114F-EB7F-59C8-8E9D-03816D8E7A42"><p> <b>Real-time signals:</b> As
+the name signifies, real-time signals inform a process about the occurrence
+of real-time events, such as high-resolution timer expiration, explicit signal
+delivery and asynchronous I/O completion. Real-time signals are different
+from non-realtime signals in the following ways: </p> <ul>
+<li id="GUID-9F352345-C466-52E2-AD82-491F7B0A8028"><p>They are delivered in
+the order they are generated. </p> </li>
+<li id="GUID-B386608A-1137-5ED0-B4FB-B78413ABA40E"><p>When a real-time signal
+is delivered to a process and is blocked, first it is queued. Later, if the
+same real-time signal is delivered to the process again, it is queued once
+again. But for non-realtime signals, the signal is queued only once (when
+it is blocked) regardless of the number of times it is delivered to a process. </p> </li>
+</ul> <p>Real-time signals are in the range <codeph>SIGRTMIN</codeph> to <codeph>SIGRTMAX</codeph>.
+You can refer to real-time signals using the notation <codeph>SIGRTMIN+n</codeph>.
+For example, <codeph>SIGRTMIN</codeph>, <codeph>SIGRTMIN+1</codeph>, <codeph>SIGRTMIN+2</codeph>,
+... <codeph>SIGRTMAX</codeph>. </p> </li>
+</ul>
+<p> <b>Note:</b> Real-time signals are subject to the same latency as non-realtime
+signals in P.I.P.S. </p>
+<p>The following topics describe how POSIX signals are emulated on the Symbian
+platform. They also describe how you can use these signals when you develop
+POSIX compliant applications or port POSIX-based applications onto the Symbian
+platform. </p>
+</conbody></concept>
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