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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-16A1C613-288D-471C-8551-51B61290E28F" xml:lang="en"><title>Application |
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13 Start-Up Time Optimization</title><shortdesc>It is important that phone users do not have to wait long for applications |
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14 to start. This document summarizes the techniques for optimizing application |
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15 start-up time.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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16 <section id="GUID-4585EAA0-4169-4C5C-A7AD-AAA7FDA529C6"> <title>Introduction</title> |
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17 <p>The techniques discussed in this document are limited in scope to |
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18 application programming. In other words, they do not require modification |
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19 of any core OS components or servers. Some of the techniques are general good |
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20 practice and are useful to developers at all levels. </p> <p>The techniques |
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21 can be summarized as follows:</p><ul> |
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22 <li><p>Avoid causing unnecessary code to be executed as an effect of your |
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23 code.</p></li> |
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24 <li><p>Defer construction of objects, loading of dynamic libraries (for example, |
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25 the application model), and starting servers until you need to use them.</p></li> |
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26 <li><p>Write efficient code!</p></li> |
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27 </ul><note>There is an inevitable trade-off between shortening the start-up |
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28 time and introducing latency elsewhere in the application. For example, if |
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29 you don’t connect to a server at start-up, you will have to do it later on, |
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30 when the application needs to use the server. This may be overcome by a central |
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31 component that coordinates background connections, or construction, such as |
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32 the view server.</note></section> |
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33 <section id="GUID-818EB735-F408-47D9-9759-A180766996B4"><title>Measure start-up |
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34 time before you start optimizing</title><p>Do not assume you know which methods |
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35 take the most time. Pay close attention to iterative and recursive operations. |
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36 Many useful tools and techniques are available to help identify poorly performing |
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37 code:</p><ul> |
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38 <li><p>Software analysis tools, for instance <xref href="http://www.glowcode.com.dita">GlowCode</xref> and |
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39 MetroWerks <xref href="http://www.metrowerks.com/MW/Develop/AMC/CodeTEST/default.htm.dita">CodeTEST</xref></p></li> |
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40 <li><p>The Symbian profiling tool, profiler.exe, which is supplied on DevKits </p></li> |
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41 <li><p>The RDebug class provides some profiling functions </p></li> |
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42 <li><p>The TTime class can be used to time blocks of code, but beware of context |
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43 switches, otherwise you may end up timing other threads!</p></li> |
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44 <li><p>Deliberately slowing down suspect blocks of code can reveal whether |
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45 or not optimizing it would bring a significant performance improvement. </p></li> |
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46 </ul></section> |
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47 <section id="GUID-594EC7CB-3477-4D0F-B489-8C1A42ED0789"><title>Defer construction |
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48 of the application model and other data members</title><p>Many applications |
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49 instantiate their components, for instance error handlers, dialogs and menus, |
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50 during start-up. In turn, each of these components may instantiate other components, |
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51 for instance menu resources and icons. This can bring some benefits, for instance |
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52 reducing application complexity, revealing memory allocation problems at start-up |
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53 rather than after the application has been running for some time and improving |
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54 the runtime performance of the application. However, to minimize application |
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55 start-up time, it is recommended to avoid this behavior. Your goal should |
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56 be to only do what is immediately necessary during start-up. </p></section> |
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57 <section id="GUID-F7BE9B30-1993-4736-9E88-F0E065BE1A3C"><title>Draw the application |
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58 as quickly as possible</title><p>During application start-up, only construct |
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59 UI components that appear in the application’s initial view. This applies |
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60 especially to the application's implementations of <codeph>CXxxApplication::CreateDocumentL()</codeph>, <codeph>CXxxDocument::ConstructL()</codeph> and <codeph>CXxxDocument::CreateAppUiL()</codeph>, all of which are called |
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61 before <codeph>CXxxAppUi::ConstructL()</codeph>. Do not read bitmaps, resources, |
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62 or any other data associated with the UI from files unless it is necessary.</p><p>In <codeph>CXxxAppUi::ConstructL()</codeph>, |
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63 make sure <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-C79D0B6F-C2D7-3F22-A62B-88762092E869"><apiname>CCoeControl::ActivateL()</apiname></xref> and <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-D5458F8C-E199-37DD-B821-050B749122C6"><apiname>CCoeControl::DrawNow()</apiname></xref> are |
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64 called on all controls that must be drawn when the application is launched. |
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65 Also ensure that the client-side window server command buffer is flushed by |
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66 calling <codeph>Flush()</codeph> on the application's window server session. |
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67 This ensures that there aren't any drawing commands left in the client-side |
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68 buffer, after <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-D5458F8C-E199-37DD-B821-050B749122C6"><apiname>CCoeControl::DrawNow()</apiname></xref> has completed. </p></section> |
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69 <section id="GUID-B320F7A3-C0E3-4A3D-8B45-AEFEDFBAAD2E"><title>Minimize the |
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70 number of bitmaps used by GUI components</title><p>Often, when a large number |
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71 of small images are required by an application, the overhead associated with |
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72 loading each bitmap outweighs any benefit associated with their size. Some |
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73 possible ways to avoid this are: </p><ul> |
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74 <li><p>use text instead, </p></li> |
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75 <li><p>for very simple graphics, draw directly using drawing primitives rather |
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76 than loading a bitmap, </p></li> |
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77 <li><p>concatenate many small bitmaps into one large bitmap file to reduce |
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78 the need to search for and load multiple files.</p></li> |
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79 </ul></section> |
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80 <section id="GUID-F00BA3FF-D9BD-44DF-A284-BAF5701179D8"><title>Reduce the |
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81 number of redraws</title><p>Some GUI components redraw themselves every time |
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82 their data changes. This may not always be necessary. Complicated GUI components |
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83 should implement their<codeph>Draw()</codeph> method to only update the area |
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84 of the screen that has changed. For example, there is no point in redrawing |
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85 a whole list box every time a new item is appended to it. In such cases, a |
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86 GUI API should allow you to switch off redrawing. Beware of GUI methods that |
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87 cause the object they are called upon to redraw itself.</p><p>Use <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-9FB682AC-0209-302A-83F3-7BCB1162B998"><apiname>CCoeControl::DrawDeferred()</apiname></xref> in |
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88 preference to <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-D5458F8C-E199-37DD-B821-050B749122C6"><apiname>CCoeControl::DrawNow()</apiname></xref> if possible, because |
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89 excessive use of <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-D5458F8C-E199-37DD-B821-050B749122C6"><apiname>CCoeControl::DrawNow()</apiname></xref> can cause GUI flicker. |
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90 For an explanation, see the documentation for <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-9FB682AC-0209-302A-83F3-7BCB1162B998"><apiname>CCoeControl::DrawDeferred()</apiname></xref>. </p></section> |
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91 <section id="GUID-71443827-BF8D-4BD8-8136-5023B6D65204"><title>Use ROM-based |
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92 bitmaps rather than filestore bitmaps</title><p>Uncompressed ROM-based bitmaps |
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93 that can be used in place from ROM are approximately three times faster to |
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94 use than filestore bitmaps. Using them can bring a significant reduction in |
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95 application start-up time.</p><p>Specifying bitmap= instead of file= in the |
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96 .OBY and .IBY files when building the ROM causes bitmaps to be uncompressed |
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97 before inclusion in the ROM. Other bitmaps need to be uncompressed at runtime, |
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98 which impacts performance. </p><p>The drawback of such bitmaps is that they |
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99 are large (up to 3 times larger than file based) and cannot be compressed, |
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100 although decompressing bitmaps should probably be avoided during start-up |
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101 anyway due to the extra processing required. </p><p>If ROM space is limited, |
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102 consider using such ROM-based bitmaps only if they are displayed during application |
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103 start-up. </p></section> |
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104 <section id="GUID-5FFD3311-DF8D-4EB1-9C76-EB9F3D306655"><title>Color depth |
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105 matching</title><p>When bitmaps are drawn to the screen, optimum performance |
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106 is achieved by ensuring that:</p><codeph>Bitmap color depth = Window color |
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107 depth = Screen device color depth </codeph><p>If this is the case, no palette |
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108 mapping between the different color depths is needed. On real hardware, this |
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109 optimization has been found to improve drawing speed by up to ten times. However, |
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110 in order to match the screen and window color depth, bitmaps may need to increase |
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111 in size and so this optimization is only possible if the increase in ROM or |
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112 RAM usage is acceptable. </p></section> |
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113 <section id="GUID-5E89E812-4B22-4B5C-A5E4-5FBE6619DC25"><title>Minimize access |
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114 to the file system</title><p>The file server can be a major bottleneck during |
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115 start-up when virtually all threads are searching for and loading data, libraries |
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116 and plug-ins. Therefore reducing file access is one of the most effective |
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117 ways to improve performance. </p></section> |
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118 <section id="GUID-9218ABF0-4062-439A-A5E9-273D76D4B711"><title>Minimize the |
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119 use of resource files</title><p>Resource files are used for localization and |
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120 allow modifications to be made to an application without the need to rebuild |
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121 it, but they are expensive to use because they require access to the file |
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122 system. </p></section> |
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123 <section id="GUID-C1CCFD4F-5C63-47C4-A312-38ACB5C16676"><title>Do not specify |
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124 a default document filename for non document-based applications</title><p>Many |
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125 applications on a smartphone do not need to use documents, for example Telephony, |
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126 Contacts (this uses the contacts database), Browser and Messaging. </p><p>By |
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127 not specifying a default document filename, hundreds of milliseconds can potentially |
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128 be saved from such applications' start-up time. </p><p>If an application |
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129 uses a document file, application start-up may involve the following steps: </p><ul> |
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130 <li><p>reading the name of the last used document file from the application’s |
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131 .ini file,</p></li> |
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132 <li><p>opening the document file, or if one doesn't exist, creating a default |
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133 document file, after reading its name from the application's resource file, </p></li> |
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134 <li><p>writing the name of the last used file to the application’s .ini file |
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135 (which is created if it doesn’t exist), </p></li> |
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136 <li><p>writing an entry to the most recently used file list (mru.dat), </p></li> |
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137 <li><p>additional document-related processing within <xref href="GUID-96CA3B4B-993F-36C0-9A5B-DF5CC74EE20E.dita#GUID-96CA3B4B-993F-36C0-9A5B-DF5CC74EE20E/GUID-E2A40307-6EB6-3ABC-B97A-63B77F565CCF"><apiname>CEikonEnv::ConstructAppFromCommandLineL()</apiname></xref>. </p></li> |
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138 </ul><p>The default document's name is read from the application's resource |
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139 file by <xref href="GUID-1185F595-0488-3E93-8D60-6B3A1A3AC32E.dita#GUID-1185F595-0488-3E93-8D60-6B3A1A3AC32E/GUID-5D851D0B-6399-3BD8-ADB5-63AD48494D47"><apiname>CEikAppUi::ProcessCommandParametersL()</apiname></xref>. There are |
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140 two ways of preventing the application from using a default document file: </p><ul> |
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141 <li><p>Give the default document a NULL name in the resource file:</p><codeph>RESOURCE |
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142 TBUF { buf=""; }</codeph></li> |
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143 <li><p>Override <xref href="GUID-1185F595-0488-3E93-8D60-6B3A1A3AC32E.dita#GUID-1185F595-0488-3E93-8D60-6B3A1A3AC32E/GUID-5D851D0B-6399-3BD8-ADB5-63AD48494D47"><apiname>CEikAppUi::ProcessCommandParametersL()</apiname></xref> to |
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144 zero the document name and return EFalse. This method is slightly more efficient |
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145 because it avoids reading the default document name from the resource file |
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146 altogether: </p><codeblock xml:space="preserve">TBool CMyAppUi::ProcessCommandParametersL(TApaCommand /*aCommand*/, TFileName& aDocumentName, const TDesC8& /*aTail*/){aDocumentName.Zero();return EFalse;}</codeblock></li> |
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147 </ul></section> |
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148 <section id="GUID-2DF939E2-C30C-4A84-90DC-92234BEB6AA0"><title>Drive scanning</title><p>This |
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149 can be a cause of unnecessary file server use. </p><p>To prevent excessive |
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150 drive access and scanning, always specify a drive letter in file paths, if |
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151 known. The omission of a drive letter will cause all available drives to be |
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152 searched in the standard Symbian platform order, in which Z: is always searched |
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153 last. </p></section> |
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154 <section id="GUID-C555545B-977F-490D-A7A7-5B6D0D0AD889"><title>Only make server |
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155 requests if you need to</title><p> Server requests involve context switching |
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156 and may cause the server to run instead of the application. In the worse case |
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157 if you make a request to a server that has not yet been started you may cause |
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158 the server to start. This will involve creating a new thread |
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159 (and possibly process) and running any server initialization code.</p></section> |
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160 <section id="GUID-1E571A30-5D8A-4647-939E-EF79B033B88E"><title>Use asynchronous |
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161 server requests instead of synchronous server requests</title><p> Synchronous |
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162 operations or methods (particularly for server requests) can cause general |
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163 application slowness, and in particular, a significant reduction in responsiveness. |
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164 Synchronous requests to servers mean your thread is waiting, so that no start-up |
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165 progress is being made. </p><p>No 'Golden Rule' exists about when to avoid |
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166 synchronous requests. However, if an asynchronous version of a method exists, |
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167 it is a good indication that the synchronous method could potentially take |
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168 some time. Whilst it may take a little extra effort to handle asynchronous |
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169 versions of method calls, you should consider very carefully any decision |
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170 to use the synchronous version. It’s often easier to change from using an |
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171 asynchronous version to synchronous than vice versa. </p><p>Note that in |
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172 some situations, you might know that the server is implementing your asynchronous |
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173 request synchronously. If this is the case, and the server runs with a higher |
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174 priority than your application, then both versions of the API may have the |
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175 same performance. However, using the synchronous version in this case has |
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176 the drawback that it relies upon knowledge of the server's implementation, |
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177 which could potentially change. </p></section> |
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178 <section id="GUID-4C7697BD-2898-4E1E-AA88-41E9F3CE2603"><title>Do not repeatedly |
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179 open and close connections to the same server</title><p> Opening a connection |
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180 to a server is an expensive operation. If an application uses a server frequently |
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181 then it should create one connection and leave it open until the application |
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182 is destroyed. R classes declared as temporaries (on the stack, in other words) |
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183 within a method may be a sign of this behavior. </p></section> |
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184 </conbody></concept> |