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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept id="GUID-2C5D53A3-0211-5C14-BD7F-E89EB27BAD2A" xml:lang="en"><title>Active |
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13 Scheduler</title><shortdesc>This document describes how active objects are queued using active |
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14 schedulers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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15 <p>Where multiple asynchronous services are used by a program, a <i>wait loop</i> is |
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16 required. </p> |
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17 <p>The <codeph>CActiveScheduler</codeph> class encapsulates the wait loop. </p> |
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18 <p>Nearly all threads use an active scheduler. Low-level test programs may |
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19 have to construct their own active scheduler, but all server threads and all |
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20 UI programs, have an active scheduler after they have initialized. If an active |
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21 scheduler is present, active objects may be added to it and removed from it |
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22 at will. </p> |
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23 <p>A thread may not have more than one active scheduler. </p> |
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24 <p>Active scheduler provides a non pre-emptive multi-tasking system, using |
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25 which active objects run on a single thread. </p> |
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26 <p>In Symbian platform, it is easier to write a system of co-operating active |
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27 objects than a system of co-operating threads. The run-time cost of an active |
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28 object is also significantly less than that of a thread. Creating and destroying |
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29 active objects is <i>very</i> much more efficient than creating and destroying |
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30 threads. </p> |
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31 <p>When the active scheduler executes its wait loop, the order in which active |
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32 objects are tested for scheduling is determined by their relative priorities. |
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33 Most active objects should have a priority of zero and there should be an |
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34 assumption that their relative position in the queue is irrelevant. No processing |
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35 should ever depend on the order in which active objects are scheduled. </p> |
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36 <section id="GUID-44BB8E7C-F310-42F5-B303-0D824AE86BA2"><title>See also</title> <p> <xref href="GUID-890F06C6-DE32-5EB1-BF0F-D41794F47AE1.dita">Active |
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37 objects</xref> </p> <p> <xref href="GUID-9C36CF76-6ED2-5674-908F-A3DF8930CEB0.dita">How |
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38 to renew a request from the active scheduler</xref>. </p> </section> |
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39 </conbody></concept> |