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+++ b/Symbian3/SDK/Source/GUID-2C5D53A3-0211-5C14-BD7F-E89EB27BAD2A.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-2C5D53A3-0211-5C14-BD7F-E89EB27BAD2A" xml:lang="en"><title>Active
+Scheduler</title><shortdesc>This document describes how active objects are queued using active
+schedulers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>Where multiple asynchronous services are used by a program, a <i>wait loop</i> is
+required. </p>
+<p>The <codeph>CActiveScheduler</codeph> class encapsulates the wait loop. </p>
+<p>Nearly all threads use an active scheduler. Low-level test programs may
+have to construct their own active scheduler, but all server threads and all
+UI programs, have an active scheduler after they have initialized. If an active
+scheduler is present, active objects may be added to it and removed from it
+at will. </p>
+<p>A thread may not have more than one active scheduler. </p>
+<p>Active scheduler provides a non pre-emptive multi-tasking system, using
+which active objects run 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 also significantly less than that of a thread. Creating and destroying
+active objects is <i>very</i> much more efficient than creating and destroying
+threads. </p>
+<p>When the active scheduler executes its wait loop, the order in which active
+objects are tested for scheduling is determined by their relative priorities.
+Most active objects should have a priority of zero and there should be an
+assumption that their relative position in the queue is irrelevant. No processing
+should ever depend on the order in which active objects are scheduled. </p>
+<section id="GUID-44BB8E7C-F310-42F5-B303-0D824AE86BA2"><title>See also</title> <p> <xref href="GUID-890F06C6-DE32-5EB1-BF0F-D41794F47AE1.dita">Active
+objects</xref>  </p> <p> <xref href="GUID-9C36CF76-6ED2-5674-908F-A3DF8930CEB0.dita">How
+to renew a request from the active scheduler</xref>. </p> </section>
+</conbody></concept>
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