Symbian3/PDK/Source/GUID-F686965A-13E5-5C0A-AED1-55EC91C79433.dita
author Dominic Pinkman <Dominic.Pinkman@Nokia.com>
Tue, 30 Mar 2010 11:56:28 +0100
changeset 5 f345bda72bc4
parent 3 46218c8b8afa
child 14 578be2adaf3e
permissions -rw-r--r--
Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<?xml version="1.0" encoding="utf-8"?>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<!-- This component and the accompanying materials are made available under the terms of the License 
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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"Eclipse Public License v1.0" which accompanies this distribution, 
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<!-- Initial Contributors:
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    Nokia Corporation - initial contribution.
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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Contributors: 
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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-->
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<!DOCTYPE concept
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<concept id="GUID-F686965A-13E5-5C0A-AED1-55EC91C79433" xml:lang="en"><title>Restrictions
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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on the use of leaves and TRAPs in destructors</title><shortdesc>Outlines the restrictions on the use of leaves and TRAPs in destructors.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>You <i>cannot</i> use <xref href="GUID-3F2CDC74-2568-371C-9D8E-34A66A619226.dita"><apiname>TRAP</apiname></xref> (and <xref href="GUID-57895C34-AD00-35E1-9BF8-478653056383.dita"><apiname>TRAPD</apiname></xref>)
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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and <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-ABF0FC5C-3334-3761-893D-D836B2EE0541"><apiname>User::Leave()</apiname></xref> in a destructor, nor in any function
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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that a destructor might call, for objects that have been placed onto the call
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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stack. <xref href="GUID-3F2CDC74-2568-371C-9D8E-34A66A619226.dita"><apiname>TRAP</apiname></xref> and <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-ABF0FC5C-3334-3761-893D-D836B2EE0541"><apiname>User::Leave()</apiname></xref> are implemented
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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in terms of C++ Try, Catch and Throw. This means that if an exception occurs,
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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the call stack is "unwound". In doing this, the destructors of objects on
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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the call stack are called. If any of these destructors subsequently throw
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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an exception, this is termed a nested exception. While a nested exception
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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is supported on the emulator (WINS), it is not supported on other hardware,
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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and there is no guarantee that the thread will terminate cleanly. </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>Symbian coding standards state that objects placed onto the call stack
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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should not have non-trivial destructors. By convention, such classes are identified
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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by names having an initial T or R. This means that such destructors should
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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not leave. </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>The following code fragment shows the kind of code that is <i>not safe</i> to
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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use: </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<codeblock id="GUID-7B2BD496-6F99-5586-B320-DB7C5DC490B9" xml:space="preserve">void f()  
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    {
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    TBar bar;
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    // Function processing.
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    ...
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    // The bar object on the call stack is automatically destroyed
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    // at function termination.
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    }
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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TBar::~TBar()
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    {
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    // The destructor calls a function that can leave.
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    // This is not permitted here.
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    doCleanUpL();
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    }</codeblock>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>You <i>can</i> use <xref href="GUID-3F2CDC74-2568-371C-9D8E-34A66A619226.dita"><apiname>TRAP</apiname></xref> (and <xref href="GUID-57895C34-AD00-35E1-9BF8-478653056383.dita"><apiname>TRAPD</apiname></xref>)
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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and <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-ABF0FC5C-3334-3761-893D-D836B2EE0541"><apiname>User::Leave()</apiname></xref> in a destructor and in any function that
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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a destructor might call, for heap-based objects, i.e. objects that are destroyed
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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by the cleanup stack. However, while this is permissible, it is not recommended
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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practice. </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>Such objects are instances of classes derived from <xref href="GUID-8F6FE089-E2A8-30F4-B67E-10F286347681.dita"><apiname>CBase</apiname></xref>,
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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and by convention such classes are identified by names having have an initial
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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C. </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>In principle, a destructor should never fail. If a destructor can leave,
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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or a function called by the destructor can leave, it suggests that the code
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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has been poorly architected. It also implies that part of the destruction
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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process might fail, potentially leading to memory or handle leaks. </p>
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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<p>One possible approach to avoid using functions that can leave within a
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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destructor is to have what might be referred to as ‘two-phase destruction’
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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where some form of <codeph>ShutdownL</codeph> function is called prior to
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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deleting the object. If there are concerns about introducing additional complexities
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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in API-usage (and greater risk), suitable guards can be introduced. One method
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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might be to store the current state of the object internally and then use
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an ASSERT to check this in the destructor. This would ensure that any usage
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errors are discovered by very simple run time testing. </p>
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<p>The following code fragment shows an example of two-phase destruction. </p>
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<codeblock id="GUID-BA3B57D6-913F-5AEC-A7AB-4EE6B915127A" xml:space="preserve">// Here, the shutdown function is a member of the class CMyClass,
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// and performs destruction activity that can leave.
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class CMyClass : public CBase
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    {
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public :
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    IMPORT_C ~CMyClass();
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    IMPORT_C void ShutdownL();
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    ...
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private :
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    TBool iStateActive
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    ...
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    }
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EXPORT_C void CMyClass::ShutdownL()
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    {
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       if (iStateActive == ETrue)
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              {
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              // Some destruction activity that can leave.
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              iStateActive = EFalse;
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              }
f345bda72bc4 Week 12 contribution of PDK documentation_content. See release notes for details. Fixes Bug 2054, Bug 1583, Bug 381, Bug 390, Bug 463, Bug 1897, Bug 344, Bug 1319, Bug 394, Bug 1520, Bug 1522, Bug 1892"
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    }
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EXPORT_C CMyClass::~CMyClass()
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    {
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       // Assert to ensure that ShutdownL() has already been called.
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       ASSERT(iStateActive == EFalse);
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    }
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</codeblock>
1
25a17d01db0c Addition of the PDK content and example code for Documentation_content according to Feature bug 1607 and bug 1608
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</conbody></concept>