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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 task |
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11 PUBLIC "-//OASIS//DTD DITA Task//EN" "task.dtd"> |
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12 <task id="GUID-3799F0DA-B99C-55BB-B44F-63B971DF1865" xml:lang="en"><title>Cleanup |
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13 Strategy Tutorial</title><shortdesc>This tutorial describes the cleanup strategy and provides details |
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14 on alternative cleanup strategies. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody> |
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15 <prereq><p>Before you start, you must: </p> <ul> |
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16 <li id="GUID-18CD0776-EEA9-56AF-9E5F-E5101BB88643"><p> <b>Deafult cleanup |
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17 strategies:</b> These are based on a template-based implementation of the |
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18 strategy design pattern. </p> </li> |
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19 <li id="GUID-598FF730-0C91-51C4-B9AA-16B74137BB6E"><p> <b>Alternative cleanup |
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20 strategies:</b> These can be specified as an optional template parameter of |
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21 the class templates for automatic resource management. </p> </li> |
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22 </ul> </prereq> |
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23 <context><p>Cleanup strategy is based on a template-based implementation of |
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24 the Strategy design pattern. The strategy design pattern is one of the most |
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25 popular, highly recommended design patterns. The vast majority of the competent |
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26 C++ developers are already familiar with the strategy (Policy) design pattern |
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27 and Policy-based design, which should improve the usability of these class |
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28 templates. </p> <p>Each |
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29 resource management class has a default cleanup strategy that is invoked when |
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30 the managing object goes out of scope. It is however possible to define an |
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31 alternative cleanup strategy when constructing the managing object. It is |
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32 also possible to define a custom cleanup strategy using the <xref href="GUID-CE0F22BA-8789-3659-87C4-164EB5862B4C.dita"><apiname>DEFINE_CLEANUP_FUNCTION</apiname></xref> macro. </p> <p> <b>Note:</b> Although |
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33 the examples below use LCleanedupX classes, the method for definfing how the |
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34 object is cleaned up is equally applicable to LManagedX classes. </p> <p>An |
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35 example code snippet is given below: </p> <codeblock id="GUID-DE45C250-C8C5-5210-B53C-D9256F00194B" xml:space="preserve"> |
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36 //Class definition of trivial R-Class |
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37 class RSimple |
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38 { |
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39 public: |
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40 |
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41 RSimple(){iData = NULL;} |
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42 |
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43 void Open(TInt aValue) |
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44 { |
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45 iData = new(ELeave) TInt(aValue); |
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46 } |
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47 |
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48 //Cleanup function – frees resource |
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49 void Close() |
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50 { |
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51 delete iData; |
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52 iData = NULL; |
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53 } |
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54 |
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55 //Cleanup function – frees resource |
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56 void Free() |
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57 { |
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58 delete iData; |
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59 iData = NULL; |
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60 } |
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61 |
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62 //Cleanup function – frees resource |
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63 void ReleaseData() |
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64 { |
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65 delete iData; |
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66 iData = NULL; |
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67 } |
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68 |
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69 //static cleanup function – frees aRSimple resources |
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70 static void Cleanup(TAny* aRSimple) |
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71 { |
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72 static_cast RSimple* (aRSimple)->Close(); |
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73 } |
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74 private: |
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75 Tint* iData; |
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76 |
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77 }; |
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78 |
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79 </codeblock> <p>The above RSimple class has three cleanup member functions, |
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80 Close, Free and ReleaseData. </p> <p>Each resource management class has a |
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81 default cleanup strategy that is invoked when the managing object goes out |
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82 of scope. The default cleanup strategy is dependent on the managing type. |
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83 Consider the example code snippet below: </p> <p> <b>Note:</b> Although the |
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84 examples below use LManagedX classes, the method for defining a custom cleanup |
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85 strategy is equally applicable to LCleanedupX classes. </p> <codeblock id="GUID-7D4F639F-3BEA-59CD-BA75-DF1C25175BA3" xml:space="preserve"> |
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86 class CTicker : public CBase |
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87 { |
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88 public: |
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89 void Tick() { ++iTicks; } |
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90 void Tock() { ++iTocks; } |
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91 |
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92 void Zap() { delete this; } |
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93 |
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94 public: |
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95 TInt iTicks; |
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96 TInt iTocks; |
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97 }; |
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98 |
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99 |
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100 class CManagedUserSinglePhase : public CBase |
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101 { |
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102 public: |
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103 . . . |
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104 |
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105 ~CManagedUserSinglePhase() |
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106 { |
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107 // The iTicker manager will automatically delete the CTicker |
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108 // The iTimer manager will automatically Close() the RTimer |
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109 } |
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110 |
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111 . . . |
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112 private: |
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113 // We have to use LManagedXxx for fields, not LCleanedupXxx |
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114 LManagedPtr CTicker iTicker; |
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115 LManagedHandle RTimer iTimer; |
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116 }; |
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117 </codeblock> <p>The default cleanup strategy for an LManagedPtr is to delete |
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118 the pointer and this is the action taken in the destructor for CManagedUserSinglePhase. </p> <p>Alternate |
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119 cleanup strategies are pre-defined in <filepath>emanaged.h</filepath> file. |
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120 It is also possible to define a custom alternate cleanup strategy that can |
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121 be passed as the second template parameter to the constructor of an LManagedX |
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122 or LCleanedupX object. </p> <p>Although the examples below use LManagedX classes, |
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123 the method for defining an alternate cleanup strategy is equally applicable |
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124 to LCleanedupX classes. </p> <p>The default cleanup strategy is to call <xref href="GUID-91F3C4E0-5687-366D-9D50-D710E763F0CF.dita#GUID-91F3C4E0-5687-366D-9D50-D710E763F0CF/GUID-29E73AC7-D397-3237-ABF9-C93C0AD39543"><apiname>CTicker::Zap()</apiname></xref> function. |
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125 It is possible however to define a custom alternate cleanup strategy as shown |
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126 below: </p> <codeblock id="GUID-5B268C52-2708-50CF-8070-0896C8CE80C0" xml:space="preserve"> |
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127 // Defines a custom pointer cleanup policy that calls the Zap member |
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128 template <class T> |
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129 class TTickerZap |
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130 { |
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131 public: |
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132 static void Cleanup(T* aPtr) |
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133 { |
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134 // The general template/class scaffolding remains the same |
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135 // for all custom cleanups, just this cleanup body varies |
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136 aPtr->Zap(); |
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137 test.Printf(_L("Zapped CTicker\n")); |
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138 } |
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139 }; |
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140 </codeblock> </context> |
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141 </taskbody><related-links> |
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142 <link href="GUID-B007634D-4D55-528A-8B85-6120C633AC8B.dita"><linktext>EUser High |
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143 Level Overview</linktext></link> |
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144 <link href="GUID-A18153C0-230C-51FB-9384-A48BB4E42F03.dita"><linktext>Clean-up |
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145 Strategy</linktext></link> |
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146 </related-links></task> |