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<concept id="GUID-3472798D-CEC5-5BA9-A3A7-D4245661DEDB" xml:lang="en"><title>pubsub: Using the Publish and Subscribe IPC Mechanism</title><shortdesc>This example demonstrates the Publish and Subscribe IPC

mechanisms using the <codeph>RProperty</codeph> class. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-909438A0-5FCA-4FA3-96EF-2666A3C07227"><title>Download</title> <p>Click on the following link to download the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-b24148a4-d20f-4af6-a0d2-d404f1a5698e.zip" scope="external">pubsub.zip</xref>.</p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-b24148a4-d20f-4af6-a0d2-d404f1a5698e.html" scope="peer">browse</xref> to view the example code.</p> </section>

<section id="GUID-20D6C064-50E0-52EE-8287-1D657C27FF75"><title>Description</title> <p>This example demonstrates three types of usage pattern for Publish

and Subscribe: </p> <ul>

<li id="GUID-12170122-3E04-5098-99C3-0C0C6B8C8914"><p>Standard State

Publishing </p> <ul>

<li id="GUID-DA65B928-6F46-5238-AED8-8CE062098621"><p> <b>Publisher:</b> The publisher defines a byte-array property and pre-allocates memory

to it. It interactively updates and re-publishes the value of the

property. </p> </li>

<li id="GUID-0519A68F-E898-5FD7-95C1-A6AA79C5CAE1"><p> <b>Subscriber:</b> The subscriber gets the value of the property defined by the publisher

by subscribing to it. It displays an error and stops running if it

fails to get the value of the property. </p> </li>

</ul> </li>

<li id="GUID-FA0336A7-3402-58BF-A987-BC3273FFB687"><p>Pure Event Distribution </p> <ul>

<li id="GUID-03D5D3D0-23F5-5E75-840E-70DC8BB74388"><p> <b>Publisher:</b> The publisher defines an integer property and publishes a random

integer value periodically. This value has no significance to the

subscriber. </p> </li>

<li id="GUID-4A3987D9-B916-584A-81C9-DC8079AA1270"><p> <b>Subscriber:</b> The subscriber gets a notification when the publisher publishes

a value. It exits when the property is deleted by the publisher. </p> </li>

</ul> </li>

<li id="GUID-FFBD46FD-D0FB-5C9A-98D8-ABA7B8C6E398"><p>Speculative

Publishing </p> <ul>

<li id="GUID-073BA0B9-1682-5642-8929-4B45738F28BD"><p> <b>Publisher:</b> The publisher does not define the property. It ignores the <codeph>KErrNotFound</codeph> error when it publishes the value of the property. </p> </li>

<li id="GUID-78B22435-963F-5E5E-9A2B-AC582DD520D4"><p> <b>Subscriber:</b> The subscriber defines and subscribes to the property. It ignores

the <codeph>KErrAlreadyExists</codeph> error. </p> </li>

</ul> </li>

</ul> </section>

<section id="GUID-63F559E8-36AB-41CD-9A2E-57080EA29601"><title>Class

summary</title><ul>

<li><p><xref href="GUID-C4776034-D190-3FC4-AF45-C7F195093AC3.dita"><apiname>RProperty</apiname></xref> - User side interface to Publish

&amp; Subscribe.</p></li>

<li><p><xref href="GUID-067293BF-B28C-3CEC-92F4-1351A795EA7F.dita"><apiname>CActive</apiname></xref> - The core class of the active object

abstraction.</p></li>

</ul></section>

<section id="GUID-43D665F1-BB55-5D5D-808E-3CBE18D2F6DA"><title>Build</title> <p>The Symbian build process describes how to build this example. </p> <p>This example builds the following binaries in

the standard location (<filepath>\epoc32\release\winscw\&lt;build_variant&gt;</filepath>) for Carbide.c++: </p> <ul>

<li id="GUID-F06CD099-75C7-5070-89E9-015AAC1F0D9A"><p> <filepath>publishstd.exe</filepath>: The publisher process for the Standard State pattern. </p> </li>

<li id="GUID-772A8A83-743C-5EE5-8D78-F1E8B60B070F"><p> <filepath>subscribestd.exe</filepath>: The subscriber process for the Standard State pattern. </p> </li>

<li id="GUID-19AD84BC-4618-518B-8F46-3DA1B1279B20"><p> <filepath>publishpe.exe</filepath>: The publisher process for the Pure Event Distribution pattern. </p> </li>

<li id="GUID-BDCCB376-3EE5-5F5B-A53D-43F52418E6AA"><p> <filepath>subscribepe.exe</filepath>: The subscriber process for the Pure Event Distribution pattern. </p> </li>

<li id="GUID-9731BBF0-0C21-5739-A9C6-4894E78A6B41"><p> <filepath>publishspec.exe</filepath>: The publisher process for the Speculative Publishing pattern. </p> </li>

<li id="GUID-0897C9AB-A30D-57A7-817C-80750877350C"><p> <filepath>subscribespec.exe</filepath>: The subscriber process for the Speculative Publishing pattern. </p> </li>

</ul> </section>

<section id="GUID-D8D0CB53-A319-55EA-8650-6F9A74DBDD6C"><title>Running

the example</title> <p>To run the example, perform the following steps

on each usage pattern: </p> <ol id="GUID-5BFB2C37-2036-542C-9CD4-672D9D18F25C">

<li id="GUID-80B81388-C636-50A0-BCCC-8F6F609E410E"><p>Open two eshells. </p> </li>

<li id="GUID-A1FF28F1-696E-593C-9FFA-54F5C96F32F2"><p>Run the publisher

executable file in one eshell. </p> </li>

<li id="GUID-E3227D02-EB36-518A-8A25-59335A27F062"><p>Run the subscriber

executable file in another eshell. </p> </li>

</ol> <p> <b>Note</b>: Switch between eshells by pressing <codeph>CTRL+ALT+SHIFT+T</codeph>. </p> </section>

<section id="GUID-935115E3-FF46-5EC1-8F36-A6AE35356AD4"><title>See

also</title> <p>For more information, see <xref href="GUID-A81C65CF-CF4E-571C-8080-9D387F46AAD6.dita">Publish and Subscribe</xref> in <i>Using User Library (E32)</i>. </p> </section>