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<concept id="GUID-16A1C613-288D-471C-8551-51B61290E28F" xml:lang="en"><title>Application Start-Up Time Optimization</title><shortdesc>It is important that phone users do not have to wait long

for applications to start. This document summarizes the techniques

for optimizing application start-up time.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-4585EAA0-4169-4C5C-A7AD-AAA7FDA529C6">       <title>Introduction</title>       <p>The techniques discussed in this document

are limited in scope to application programming. In other words, they

do not require modification of any core OS components or servers.

Some of the techniques are general good practice and are useful to

developers at all levels. </p>     <p>The techniques can be summarized

as follows:</p><ul>

<li><p>Avoid causing unnecessary code to be executed as an effect

of your code.</p></li>

<li><p>Defer construction of objects, loading of dynamic libraries

(for example, the application model), and starting servers until you

need to use them.</p></li>

<li><p>Write efficient code!</p></li>

</ul><note>There is an inevitable trade-off between shortening the

start-up time and introducing latency elsewhere in the application.

For example, if you don’t connect to a server at start-up, you will

have to do it later on, when the application needs to use the server.

This may be overcome by a central component that coordinates background

connections, or construction, such as the view server.</note></section>

<section id="GUID-818EB735-F408-47D9-9759-A180766996B4"><title>Measure

start-up time before you start optimizing</title><p>Do not assume

you know which methods take the most time. Pay close attention to

iterative and recursive operations. Many useful tools and techniques

are available to help identify poorly performing code:</p><ul>

<li><p>Software analysis tools, for instance <xref href="http://www.glowcode.com" scope="external">GlowCode</xref> and

MetroWerks <xref format="html" href="http://www.metrowerks.com/MW/Develop/AMC/CodeTEST/default.htm" scope="external">CodeTEST</xref></p></li>

<li><p>The Symbian profiling tool, profiler.exe, which is supplied

on DevKits </p></li>

<li><p>The RDebug class provides some profiling functions </p></li>

<li><p>The TTime class can be used to time blocks of code, but beware

of context switches, otherwise you may end up timing other threads!</p></li>

<li><p>Deliberately slowing down suspect blocks of code can reveal

whether or not optimizing it would bring a significant performance

improvement. </p></li>

</ul></section>

<section id="GUID-594EC7CB-3477-4D0F-B489-8C1A42ED0789"><title>Defer

construction of the application model and other data members</title><p>Many applications instantiate their components, for instance error

handlers, dialogs and menus, during start-up. In turn, each of these

components may instantiate other components, for instance menu resources

and icons. This can bring some benefits, for instance reducing application

complexity, revealing memory allocation problems at start-up rather

than after the application has been running for some time and improving

the runtime performance of the application. However, to minimize application

start-up time, it is recommended to avoid this behavior. Your goal

should be to only do what is immediately necessary during start-up. </p></section>

<section id="GUID-F7BE9B30-1993-4736-9E88-F0E065BE1A3C"><title>Draw

the application as quickly as possible</title><p>During application

start-up, only construct UI components that appear in the application’s

initial view. This applies 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 before <codeph>CXxxAppUi::ConstructL()</codeph>. Do not

read bitmaps, resources, or any other data associated with the UI

from files unless it is necessary.</p><p>In <codeph>CXxxAppUi::ConstructL()</codeph>, 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 called on all controls that

must be drawn when the application is launched. Also ensure that the

client-side window server command buffer is flushed by calling <codeph>Flush()</codeph> on the application's window server session. This

ensures that there aren't any drawing commands left in the client-side

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>

<section id="GUID-B320F7A3-C0E3-4A3D-8B45-AEFEDFBAAD2E"><title>Minimize

the number of bitmaps used by GUI components</title><p>Often, when

a large number of small images are required by an application, the

overhead associated with loading each bitmap outweighs any benefit

associated with their size. Some possible ways to avoid this are: </p><ul>

<li><p>use text instead, </p></li>

<li><p>for very simple graphics, draw directly using drawing primitives

rather than loading a bitmap,  </p></li>

<li><p>concatenate many small bitmaps into one large bitmap file to

reduce the need to search for and load multiple files.</p></li>

</ul></section>

<section id="GUID-F00BA3FF-D9BD-44DF-A284-BAF5701179D8"><title>Reduce

the number of redraws</title><p>Some GUI components redraw themselves

every time their data changes. This may not always be necessary. Complicated

GUI components should implement their<codeph>Draw()</codeph> method

to only update the area of the screen that has changed. For example,

there is no point in redrawing a whole list box every time a new item

is appended to it. In such cases, a GUI API should allow you to switch

off redrawing. Beware of GUI methods that 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 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 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. 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>

<section id="GUID-71443827-BF8D-4BD8-8136-5023B6D65204"><title>Use

ROM-based bitmaps rather than filestore bitmaps</title><p>Uncompressed

ROM-based bitmaps that can be used in place from ROM are approximately

three times faster to use than filestore bitmaps. Using them can bring

a significant reduction in application start-up time.</p><p>Specifying

bitmap= instead of file= in the .OBY and .IBY files when building

the ROM causes bitmaps to be uncompressed before inclusion in the

ROM. Other bitmaps need to be uncompressed at runtime, which impacts

performance.   </p><p>The drawback of such bitmaps is that they are

large (up to 3 times larger than file based) and cannot be compressed,

although decompressing bitmaps should probably be avoided during start-up

anyway due to the extra processing required.   </p><p>If ROM space

is limited, consider using such ROM-based bitmaps only if they are

displayed during application start-up. </p></section>

<section id="GUID-5FFD3311-DF8D-4EB1-9C76-EB9F3D306655"><title>Color

depth matching</title><p>When bitmaps are drawn to the screen, optimum

performance is achieved by ensuring that:</p><codeph>Bitmap color

depth = Window color depth = Screen device color depth </codeph><p>If this is the case, no palette mapping between the different color

depths is needed. On real hardware, this optimization has been found

to improve drawing speed by up to ten times. However, in order to

match the screen and window color depth, bitmaps may need to increase

in size and so this optimization is only possible if the increase

in ROM or RAM usage is acceptable. </p></section>

<section id="GUID-5E89E812-4B22-4B5C-A5E4-5FBE6619DC25"><title>Minimize

access to the file system</title><p>The file server can be a major

bottleneck during start-up when virtually all threads are searching

for and loading data, libraries and plug-ins. Therefore reducing file

access is one of the most effective ways to improve performance. </p></section>

<section id="GUID-9218ABF0-4062-439A-A5E9-273D76D4B711"><title>Minimize

the use of resource files</title><p>Resource files are used for localization

and allow modifications to be made to an application without the need

to rebuild it, but they are expensive to use because they require

access to the file system. </p></section>

<section id="GUID-C1CCFD4F-5C63-47C4-A312-38ACB5C16676"><title>Do

not specify a default document filename for non document-based applications</title><p>Many applications on a smartphone do not need to use documents,

for example Telephony, Contacts (this uses the contacts database),

Browser and Messaging.   </p><p>By not specifying a default document

filename, hundreds of milliseconds can potentially be saved from such

applications' start-up time.   </p><p>If an application uses a document

file, application start-up may involve the following steps: </p><ul>

<li><p>reading the name of the last used document file from the application’s

.ini file,</p></li>

<li><p>opening the document file, or if one doesn't exist, creating

a default document file, after reading its name from the application's

resource file, </p></li>

<li><p>writing the name of the last used file to the application’s

.ini file (which is created if it doesn’t exist),  </p></li>

<li><p>writing an entry to the most recently used file list (mru.dat), </p></li>

<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>

</ul><p>The default document's name is read from the application's

resource 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 two ways of preventing the application from using a default

document file: </p><ul>

<li><p>Give the default document a NULL name in the resource file:</p><codeph>RESOURCE TBUF { buf=""; }</codeph></li>

<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 zero the document name and return EFalse. This method is slightly

more efficient because it avoids reading the default document name

from the resource file altogether: </p><codeblock xml:space="preserve">TBool CMyAppUi::ProcessCommandParametersL(TApaCommand /*aCommand*/, TFileName&amp; aDocumentName, const TDesC8&amp; /*aTail*/){aDocumentName.Zero();return EFalse;}</codeblock></li>

</ul></section>

<section id="GUID-2DF939E2-C30C-4A84-90DC-92234BEB6AA0"><title>Drive

scanning</title><p>This can be a cause of unnecessary file server

use.   </p><p>To prevent excessive drive access and scanning, always

specify a drive letter in file paths, if known. The omission of a

drive letter will cause all available drives to be searched in the

standard Symbian platform order, in which Z: is always searched last. </p></section>

<section id="GUID-C555545B-977F-490D-A7A7-5B6D0D0AD889"><title>Only

make server requests if you need to</title><p> Server requests involve

context switching and may cause the server to run instead of the application.

In the worse case if you make a request to a server that has not yet

been started you may cause the server to start. This will involve

creating a new thread (and possibly process) and running any server

initialization code.</p></section>

<section id="GUID-1E571A30-5D8A-4647-939E-EF79B033B88E"><title>Use

asynchronous server requests instead of synchronous server requests</title><p> Synchronous operations or methods (particularly for server requests)

can cause general application slowness, and in particular, a significant

reduction in responsiveness. Synchronous requests to servers mean

your thread is waiting, so that no start-up progress is being made.

  </p><p>No 'Golden Rule' exists about when to avoid synchronous requests.

However, if an asynchronous version of a method exists, it is a good

indication that the synchronous method could potentially take some

time. Whilst it may take a little extra effort to handle asynchronous

versions of method calls, you should consider very carefully any decision

to use the synchronous version. It’s often easier to change from using

an asynchronous version to synchronous than vice versa.   </p><p>Note

that in some situations, you might know that the server is implementing

your asynchronous request synchronously. If this is the case, and

the server runs with a higher priority than your application, then

both versions of the API may have the same performance. However, using

the synchronous version in this case has the drawback that it relies

upon knowledge of the server's implementation, which could potentially

change. </p></section>

<section id="GUID-4C7697BD-2898-4E1E-AA88-41E9F3CE2603"><title>Do

not repeatedly open and close connections to the same server</title><p> Opening a connection to a server is an expensive operation. If

an application uses a server frequently then it should create one

connection and leave it open until the application is destroyed. R

classes declared as temporaries (on the stack, in other words) within

a method may be a sign of this behavior. </p></section>

</conbody></concept>