--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Symbian3/SDK/Source/GUID-AAA2ABA4-5555-5E4B-AEFF-3DF61462B170.dita	Wed Mar 31 11:11:55 2010 +0100
@@ -0,0 +1,31 @@
+<?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-AAA2ABA4-5555-5E4B-AEFF-3DF61462B170" xml:lang="en"><title>Introduction
+to asynchronous programming</title><shortdesc>This document introduces the concept of asynchronous programming.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>When a program requests a service, this service can be performed either <i>synchronously</i> or <i>asynchronously</i>. </p>
+<p>A synchronous service is the normal pattern for function calls where the
+function returns and the service requested has either performed successfully
+or has failed and an error code returned.</p>
+<p>An asynchronous service is <i>requested</i> by a function call but completion
+occurs later. Completion is indicated by a <i>signal</i>. Between the issue
+of the request and the signal, the request is said to be <i>pending</i>. The
+requesting program can do other processing while the request is pending or
+it can issue a <i>wait</i>. The operating system wakes the program up when
+completion of any of its pending requests is signalled.</p>
+<p>A program may contain a number of independently-executing units, called
+threads. All programs have a primary thread, and may create other threads,
+possibly for providing or using asynchronous services.</p>
+<p>If all threads are in a wait state, for example, waiting for user input,
+Symbian platform powers down as much as possible of the machine’s electronics.
+This results in battery savings and, consequently, a considerable extension
+of useful battery life.</p>
+</conbody></concept>
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