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+++ b/Symbian3/SDK/Source/GUID-2B8D3611-5B97-50E7-A9DD-23626A8EFB45.dita	Thu Jan 21 18:18:20 2010 +0000
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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-2B8D3611-5B97-50E7-A9DD-23626A8EFB45" xml:lang="en"><title>Introduction
+to active objects and the active scheduler</title><shortdesc>This document provides a short introduction to active objects and
+active schedulers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<section id="GUID-A139EAE2-5471-496C-B584-DE10D7415CD3"><title>Active objects</title> <p>An active object is a convenient
+encapsulation of the behaviour involved in making requests to an asynchronous
+service provider and handling the completion of those requests. Specifically,
+it encapsulates the service provider's request, cancel functions and the function
+which handles the completion of those requests. </p> <p>Some asynchronous
+service providers supply active object based classes as interfaces through
+which clients access them. </p> <p>An active object is an instance of a <codeph>CActive</codeph> derived
+class. </p> </section>
+<section id="GUID-73A2BF4F-AE0A-4357-AE75-EA5AA678109F"><title>The active scheduler</title> <p>An active scheduler encapsulates
+the wait loop which is at the heart of all programs using multiple asynchronous
+services. </p> <p>An active scheduler is an instance of a <codeph>CActiveScheduler</codeph> class
+or, in some circumstances, an instance of a <codeph>CActiveScheduler</codeph> <i>derived</i> class. </p> <p>Active
+objects, together with the active scheduler, provide a system of non pre-emptive
+multi-tasking which runs on a single thread. </p> <p>In Symbian platform,
+it is easier to write a system of co-operating active objects than a system
+of co-operating threads. The run-time cost of an active object is significantly
+less than that of a thread. Creating and destroying active objects is more
+efficient than creating and destroying threads. </p> <p><b>See
+also</b> </p> <p> <xref href="GUID-C0C19F93-D804-5AED-90E4-A814FA6A3732.dita">Low
+Level Asynchronous Service Handling</xref> </p> </section>
+</conbody></concept>
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