diff -r 43e37759235e -r 51a74ef9ed63 Symbian3/SDK/Source/GUID-50BE8F1A-513A-433C-B045-66658FC226D7.dita
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Symbian3/SDK/Source/GUID-50BE8F1A-513A-433C-B045-66658FC226D7.dita	Wed Mar 31 11:11:55 2010 +0100
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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-50BE8F1A-513A-433C-B045-66658FC226D7" xml:lang="en"><title>Client/server
+communication</title><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p><xref href="GUID-E530CBB9-C20D-5426-89AA-DC0281C05381.dita">Inter Process
+Communication</xref> (IPC) is the basis for client/server architecture. Clients
+and servers run in different threads, although not necessarily in different
+processes, and communicate through message passing protocol. There are no
+direct pointers between the parties, leaving the integrity of the server and
+its resources untouched by clients. For more information, see <xref href="GUID-D4C7A714-F7BB-5A8D-A875-4796395B9B6C.dita">Introduction
+to the client/server architecture</xref>.</p>
+<p>Communication between the client and the server is managed by <xref href="GUID-E651C7A7-D6EB-533E-A97A-360D089DE7A5.dita">Inter-thread data transfer</xref>.
+Only the server and its clients can decode the parameters of the message.
+This is also a security feature, because process boundaries are separators
+of memory space, direct pointers to the client's data structures cannot be
+delivered. All data not fitting in the provided integers must be represented
+as a <xref href="GUID-261ADCEC-C8C8-46E3-A7DC-804AC868C233.dita">descriptor</xref>,
+and an address to the descriptor (or actually a <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/TPckgClass.html" format="application/java-archive">TPckg</xref></codeph> object)
+is delivered within the message. The server then uses safe inter-thread read
+and write functions to access the provided descriptor.</p>
+<p>The following figure shows the relationship of the <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/e32cmn.hGlobals.html#%3a%3aTDesC" format="application/java-archive">TDesC</xref></codeph> and <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/TPckgClass.html" format="application/java-archive">TPckg</xref></codeph> classes.</p>
+<fig id="GUID-715F1B96-AFC4-4FB2-AF51-6E720077F83A"><title>Relationship of a message package and a descriptor class</title><image href="GUID-D99BA4CA-9823-4968-953D-36AA7F266B39_d0e10779_href.png"/></fig>
+<p>Consider the following issues when implementing the client-side API:</p>
+<ul>
+<li><p>Determine if the server is already running with the <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/TFindServerClass.html" format="application/java-archive">TFindServer</xref></codeph> class. If not, then it should be launched.</p></li>
+<li><p>Once the server is running, create the connection with <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/RSessionBaseClass.html" format="application/java-archive">RSessionBase::CreateSession</xref></codeph> and make sure there are free message slots available to avoid lost
+messages.</p></li>
+<li><p>When packaging message arguments, make sure they are in a
+format that the server understands. For more information, see <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/TIpcArgsClass.html" format="application/java-archive">TIpcArgs</xref></codeph>.</p></li>
+</ul>
+</conbody></concept>
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