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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.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 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& aDocumentName, const TDesC8& /*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>