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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-6D8460DF-8B0F-5249-B236-92ABE0E67A14" xml:lang="en"><title>Memory
+Allocation Overview</title><shortdesc>Provides low-level functionality by which a Symbian platform process
+can access and manipulate memory areas.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<section id="GUID-B6FA381B-2A42-4D5A-9511-DC634E8AF6C2"><title>Purpose</title> <p>Most client programs do not
+need to use this functionality directly. They are used by programs that are
+explicitly concerned about sharing memory areas between threads within a process,
+or between processes. </p> </section>
+<section id="GUID-39581657-1B46-436B-A8F2-A3F7AB525DA4"><title>Description</title> <p>The API has two key concepts: chunk
+and heap. </p> <p><b>Chunk</b> </p> <p>A
+chunk defines a contiguous region of virtual addresses. It represents memory
+that is addressable by running code. A chunk is the fundamental way in which
+Symbian platform allocates memory and makes it available to running code. </p> <p>The
+range of addressable memory is also referred to as <i>reserved</i> memory. </p> <p>Physical
+addresses representing either memory storage like RAM, or memory-mapped I/O
+devices, are mapped into a subset of a chunk's reserved memory. Such memory
+is said to be <i>committed</i>. </p> <p>When a process is created, it contains
+at least two chunks: </p> <ul>
+<li id="GUID-143BBF82-BAA5-5548-83AC-54DF2067C058"><p>a chunk that contains: </p> <ul>
+<li id="GUID-2A57D6BD-83FD-5C4B-B5AC-CA1BACDD5CB7"><p>the process executable's <codeph>.data</codeph> section
+(initialised global and writable static data) </p> </li>
+<li id="GUID-F6D7AB82-BEB5-5052-9723-B190F12A47ED"><p>the process executable's <codeph>.bss</codeph> section
+(zero filled data) </p> </li>
+<li id="GUID-DC6E22B6-9E12-5181-99DB-D6C2154C513A"><p>user-side stack space
+for all threads that run in that process. </p> </li>
+</ul> </li>
+<li id="GUID-73016FAD-8F84-596C-B048-CD1E1B05AA8B"><p>a chunk to contain the
+heap used by the main thread of the process. </p> </li>
+</ul> <p>If the process executable is loaded into RAM (i.e. it is not ROM
+resident), then there is another chunk to contain the code. </p> <p>On ARM
+processors up to and including those that support the ARMv5 architecture,
+the memory model used by Symbian platform is the <i>moving memory model</i>.
+To guarantee real-time behaviour using this model, each process is limited
+to a maximum of 16 chunks. This means that a program can create up to 14 additional
+chunks. Where the process executable is loaded into RAM, the chunk containing
+the code is effectively global and does not contribute to the 16 chunk per
+process limit. </p> <p>On ARM processors that support the ARMv6 architecture,
+the memory model used by Symbian platform is the <i>multiple memory model</i>.
+Using this model, there is no limit on the number of chunks per process. Where
+the process executable is loaded into RAM, the chunk containing the code is
+specific to the process. </p> <p> <xref href="GUID-DA41F070-0E54-3F8A-B301-39A0C6AFAB38.dita"><apiname>TFindChunk</apiname></xref> is used for
+finding a global chunk created by another process. </p> <p>The user-side interface
+to a chunk is provided by an instance of the <xref href="GUID-326A2F4D-0E99-31C0-A35D-E8BF45913F07.dita"><apiname>RChunk</apiname></xref> class. </p> <p><b>Heap</b> </p> <p>A heap is used for explicit dynamic allocation of memory.
+Symbian platform defines C++'s <codeph>new</codeph> operator to create objects
+on the current thread's heap. </p> <p>Heaps may be: </p> <ul>
+<li id="GUID-1ADAF0B8-BB72-5D07-BEA9-359DEFFC25E3"><p>monitored for memory
+leaks: this happens automatically for GUI applications </p> </li>
+<li id="GUID-0F5F3E02-F1E1-56D0-9865-D3DFA440DCF0"><p>shared between threads
+within a process </p> </li>
+<li id="GUID-ED409A70-ECD3-5EE9-9245-42FDEF5CCA42"><p>accessed and manipulated
+at the cell level </p> </li>
+</ul> <p>The heap interface is provided by the <xref href="GUID-9DB4A58C-6FC8-3292-A547-4C161BD188FC.dita"><apiname>RAllocator</apiname></xref> and <xref href="GUID-C5475104-B67A-3722-B11D-DBB930423492.dita"><apiname>MAllocator</apiname></xref> classes.
+This interface is abstract so that device manufacturers can implement heaps
+with different allocation algorithms. Symbian platform provides the <xref href="GUID-EFAFDD75-7E59-306A-882D-317F5564979E.dita"><apiname>RHeap</apiname></xref> class
+as a default heap implementation. In practice, there is no need to know about
+implementation details. </p> <p>When managing the current thread's heap, it
+is more convenient to use the equivalent functions provided by the System
+Static Functions API; this is the <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita"><apiname>User</apiname></xref> class. For example, <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-C035F07D-B6D9-3A21-A323-DAC89137280D"><apiname>User::AllocL()</apiname></xref>.
+The System Static Functions API also provides macros that conveniently wrap
+calls for monitoring heap usage for memory leaks. </p> </section>
+<section id="GUID-7A3524D6-AA39-49A2-9DBC-E3EAEA654A7B"><title>See also</title> <p> <xref href="GUID-506642C2-A14F-55F2-9377-43DDB14F4053.dita">Raw
+Memory Overview</xref>  </p> <p> <xref href="GUID-FF8F5D97-7D37-5F6B-84A3-C064E2FD53E0.dita">System
+Static Functions Overview</xref>  </p> <p> <xref href="GUID-5D4B86D3-20C4-5D87-A6C1-225018D32347.dita">Thread
+And Process Management Overview</xref>  </p> </section>
+</conbody></concept>
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