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<concept id="GUID-2EE70A59-7EF0-5A1B-986B-00ED5ACD8BD4" xml:lang="en"><title>Patchable
Constants: KListImplBufferSize</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<codeblock id="GUID-A819292B-1CC3-5378-82E8-01ECBCA1EF1C" xml:space="preserve"># define ECOM_PATCHDATA_KLISTIMPLBUFFERSIZE 2048</codeblock>
<table id="GUID-5C9F05F1-89BD-5AE1-9C12-217EE4AE91A6">
<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>
<tbody>
<row>
<entry><p>Exported from: </p> </entry>
<entry><p> <filepath>ECOMPATCHDATA.DLL</filepath>  </p> </entry>
</row>
<row>
<entry><p>Defined in: </p> </entry>
<entry><p> <filepath>                 .../os/ossrv/lowlevellibsandfws/pluginfw/framework/frame/ecompatchdataconstant.cpp</filepath> </p> </entry>
</row>
<row>
<entry><p>Purpose: </p> </entry>
<entry><p>This constant is used to define the size of the buffer that is pre-allocated
on the ECOM client side to hold the list of Implementation Information records.
The records are copied from the server as a result of a call to one of the <xref href="GUID-1344F049-81C4-3D17-AF46-8B5584680ADB.dita#GUID-1344F049-81C4-3D17-AF46-8B5584680ADB/GUID-AE9D4F24-8554-3151-AAF3-D63F400821C4"><apiname>REComSession::ListImplementationsL()</apiname></xref> functions. </p> <p>If the result of a call to <codeph>ListImplementationsL()</codeph> does
not fit into the initial buffer, the server stores the result and tells the
client the required size. <codeph>ListImplementationsL()</codeph> then reallocates
the buffer and makes a second call to the server to retrieve the results. </p> <p>This
value can be adjusted during ROM build time to suit a particular device. In
general, a smaller value results in more client-server requests, while a larger
value results in fewer client-server requests. Care must be taken when choosing
the value. A large value, increases the temporary heap consumption by ECOM
client processes, but results in faster completion of the call to <codeph>ListImplementationsL()</codeph> because
of fewer client-server calls. System start-up can benefit from fine-tuning
this value. </p> <p>The default size is 2048 bytes. This value optimises performance
on the Symbian test UI platform. Larger values do not result in any significant
gain in performance; smaller values reduce performance. </p> <p>To work out
the optimum value for this constant, you need to discover the typical size
of the buffer required for each call to <codeph>ListImplementationsL()</codeph>.
To get such values, you need to enable the <codeph>ECOM_TRACE</codeph> macro
and rebuild <codeph>ECOM</codeph>. After booting up the device, you will see
output in the following format from the serial port: </p> <codeblock id="GUID-13659F9E-02AC-5752-BE1B-DC08E351A8BC" xml:space="preserve">ECOM ListImplementations request buffer size required=88</codeblock> <codeblock id="GUID-28532E84-E2BA-59F8-9E9A-7B144FD2BF90" xml:space="preserve">ECOM ListImplementations request buffer size required=1562</codeblock> <p> </p> <p>You
can use this information to calculate mean and median values, which will help
you to choose the optimum value for your platform. </p> </entry>
</row>
</tbody>
</tgroup>
</table>
<p>ECom uses a customized scheme to handle patchable constants. Device creators
should follow the scheme described below to set patch values: </p>
<ul>
<li id="GUID-E3EFD7AA-7B91-5CF9-8E9E-F027C35C167D"><p>Each patchable constant
is represented by a macro listed in <filepath>\epoc32\rom\include\ecompatchconstants.hby</filepath>.
The macros in the HBY file are all commented out. </p> </li>
<li id="GUID-51E1005E-60FF-55CF-8D51-BEAE67E38D7A"><p>To activate a patch
macro, uncomment the line and change the example value in the line to your
custom value. </p> </li>
</ul>
</conbody></concept>