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<concept id="GUID-242D9F27-401B-4230-B3A6-11E2D9D3DE17" xml:lang="en"><title>Threading

Model</title><shortdesc>Describes the impacts of thread execution in SMP environment.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>In single core system, the active threads are executed in a time-sliced

fashion and appear to run in parallel. In a multi-core environment, multiple

threads can be executed in parallel and can also use time-sliced thread execution. </p>

<section id="GUID-54670F76-522D-48FC-8D71-397E0E14D9DE"><title>Single-threaded

code</title>The applications designed with single threads will not have any

performance benefit by using multiple cores. The contention for CPU usage

may be reduced on multi-core hardware. The single threaded code should run

normally on multi-core hardware. Some code is more efficient

having single threads and some code performs better with multiple threads.<note> It

is not recommended to modify a single-threaded application into multi-threaded

code until the existing code runs safely on multiple-core hardware. But new

applications can be designed to be multi-threaded to take advantage of the

SMP hardware.</note></section>

<section id="GUID-80EF734A-69F4-4B21-B031-F22D23721629"><title>Servers</title><p>Most

servers on Symbian platform are single threaded and are unlikely to need any

modification to migrate to a multi-core hardware. Some servers may need to

service multiple clients concurrently. One of the solutions to take advantage

of SMP hardware is to modify the servers to have multiple threads to service

the clients concurrently. The performance can also be improved by implementing

caching in the server. </p></section>

<section id="GUID-DA500B10-CE4F-4640-A203-A06E0DD63C10"><title>Active scheduler</title><p>Active

schedulers are designed to be single threaded and the active objects never

run concurrently because there is no need for a lock in the data shared between

active objects. The active scheduler will only execute one active object at

a time. The existing code should run safely on multi-core hardware. If the

active objects need to use multiple cores then the code should be modified

to be multi-threaded and use locks when there is shared data between the threads. </p></section>

<section id="GUID-31F8B40D-507B-458A-847F-2982FA06989D"><title>User-side code</title><p>The

user-side applications that use Symbian platform Inter Process Communication

(IPC) functions like <xref href="GUID-B0E661BC-4058-3256-B9C3-5A4FD52F6DE5.dita#GUID-B0E661BC-4058-3256-B9C3-5A4FD52F6DE5/GUID-83AADCC6-1AD8-32D8-A6E6-B86B47C97DC2"><apiname>RThread::Rendezvous()</apiname></xref>, <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-2F263A1B-BB71-396C-8C45-B0D062327FFA"><apiname>User::RequestComplete()</apiname></xref>, <xref href="GUID-9741288A-B0EE-3098-B891-43124FF056BB.dita#GUID-9741288A-B0EE-3098-B891-43124FF056BB/GUID-5ACB4970-55CA-3ECD-8388-C9CE9CFF103E"><apiname>RSession::SendReceive()</apiname></xref> or Publish-Subscribe should run safely on multi-core hardware. If the user-side

code uses some proprietary IPC mechanism to communicate with other process,

that code may need to be modified to use Symbian IPC functions. </p><table id="GUID-114D4D3D-C28E-43BE-85CA-01DCAD2B944B">

<desc>The following table compares the advantages of single-threaded and multi-threaded

applications on an SMP hardware:</desc>

<tgroup cols="2"><colspec colname="col1"/><colspec colname="col2"/>

<thead>

<row>

<entry valign="top">Single-threaded applications</entry>

<entry valign="top">Multi-threaded applications</entry>

</row>

</thead>

<tbody>

<row>

<entry>Low CPU usage for schedulers</entry>

<entry>Parallel execution provides faster execution</entry>

</row>

<row>

<entry>Low memory overhead</entry>

<entry>Added control on power consumption</entry>

</row>

<row>

<entry>Low cache overhead</entry>

<entry>Servers that have to service multiple clients can run on different

CPUs</entry>

</row>

</tbody>

</tgroup>

</table></section>

</conbody><related-links>

<link href="GUID-387E98B0-568D-4DBB-9A9E-616E41E96B58.dita"><linktext>SMP Overview</linktext>

</link>