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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>       <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><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.dita">GlowCode</xref> and

MetroWerks <xref href="http://www.metrowerks.com/MW/Develop/AMC/CodeTEST/default.htm.dita">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><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><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 <xref href="GUID-05A12A50-93A3-3F3E-842F-81EF47D78F7F.dita#GUID-05A12A50-93A3-3F3E-842F-81EF47D78F7F/GUID-172521B0-E7C8-3214-AA4D-814A9C98216C"><apiname>CXxxApplication::CreateDocumentL()</apiname></xref>, <xref href="GUID-8001206A-3B19-381F-96F6-350336FDFBF2.dita#GUID-8001206A-3B19-381F-96F6-350336FDFBF2/GUID-453AFFB0-6711-3881-97E6-0BB9E5185E06"><apiname>CXxxDocument::ConstructL()</apiname></xref> and <xref href="GUID-8001206A-3B19-381F-96F6-350336FDFBF2.dita#GUID-8001206A-3B19-381F-96F6-350336FDFBF2/GUID-DCC1BAD5-95AB-3308-9132-2780852BA913"><apiname>CXxxDocument::CreateAppUiL()</apiname></xref>, all of which are called before <xref href="GUID-3C72B6B6-F1B3-3C36-B69A-5074E5EDC32A.dita#GUID-3C72B6B6-F1B3-3C36-B69A-5074E5EDC32A/GUID-5C26B1AB-6917-3133-9CD8-34AFCA9524B9"><apiname>CXxxAppUi::ConstructL()</apiname></xref>.

Do not read bitmaps, resources, or any other data associated with the UI from

files unless it is necessary.</p><p>In <xref href="GUID-3C72B6B6-F1B3-3C36-B69A-5074E5EDC32A.dita#GUID-3C72B6B6-F1B3-3C36-B69A-5074E5EDC32A/GUID-5C26B1AB-6917-3133-9CD8-34AFCA9524B9"><apiname>CXxxAppUi::ConstructL()</apiname></xref>,

make sure <xref href="GUID-6965379F-00B9-38DB-9AF3-9DAD55DEBBB7.dita"><apiname>ActivateL()</apiname></xref> and <xref href="GUID-0F226BB0-2D2F-3BD5-A439-C25F7DEACE85.dita"><apiname>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 <xref href="GUID-09D06EF8-E231-3A76-A4F0-267B9CD83B54.dita"><apiname>Flush(</apiname></xref>) 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-0F226BB0-2D2F-3BD5-A439-C25F7DEACE85.dita"><apiname>DrawNow()</apiname></xref> has completed. </p></section>

<section><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><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 <xref href="GUID-AC3B79CA-A2FE-395E-9BCE-4630AF6910AC.dita"><apiname>Draw()</apiname></xref> 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-811046A4-4272-3B29-80D9-CB897C4E1DD0"><apiname>CCoeControl::DrawDeferred(</apiname></xref>) in preference

to <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-70FF46AE-5ACC-36F1-97F0-CBD847779C19"><apiname>CCoeControl::DrawNow(</apiname></xref>) if possible, because excessive

use of <xref href="GUID-65BA28DB-77C6-3075-80E7-84E98780FD19.dita"><apiname>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><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><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><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><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><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><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

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

<section><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><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><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>