--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Symbian3/SDK/Source/GUID-8EAB97D5-267A-58CC-BC3E-5CB1D72CB7ED.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-8EAB97D5-267A-58CC-BC3E-5CB1D72CB7ED" xml:lang="en"><title>Non
+pre-emptive servicing</title><shortdesc>This document describes how requests to active objects are serviced
+non pre-emptively.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>The UI server frameworks spend most of their time waiting for some event
+to occur, and then spend a <i>short</i> time executing a <codeph>RunL()</codeph> function
+to service that event. When one event has been serviced, processing returns
+to the wait loop in the active scheduler allowing other events to be serviced.</p>
+<p>If a second request completes while the <codeph>RunL()</codeph> function
+is handling completion of the first request, then another call to <codeph>RunL()</codeph> to
+handle completion of the second request cannot be scheduled until the first
+invocation of <codeph>RunL()</codeph> is complete.</p>
+<p>This means that active object scheduling is non pre-emptive.</p>
+<p>Active objects are queued from the active scheduler in order of priority.
+The priority is usually determined at the time that the active object is constructed,
+although it can be changed later.</p>
+<p>If several requests complete while a <codeph>RunL()</codeph> function is
+handling the completion of earlier request, the active scheduler takes the
+first active object (i.e. the one with the highest priority) with a completed
+request and calls its <codeph>RunL()</codeph> function.</p>
+<p>As scheduling is non pre-emptive, a high-priority request cannot be serviced
+until the previously running request’s <codeph>RunL()</codeph> has completed.</p>
+<section id="GUID-55AEDDD4-72FB-4865-90AF-D4F9C5B47582"><title>Recommendations for active object priority</title> <p>Most
+active objects should have a priority of <codeph>TPriority::EPriorityStandard</codeph> and
+processing should not depend on the order in which active objects are scheduled.</p> <p>However,
+any active object involved in user input should have a higher priority over
+other active objects to ensure responsiveness and to allow user control over
+a device.</p> <p>Long running and background services should have a low priority.</p> </section>
+</conbody></concept>
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