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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 <apiname>RProperty</apiname> 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><xref href="GUID-3100800B-B2F7-50EF-BD4C-3C345ECCB2A5.dita">The Symbian OS build process</xref> 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>

</conbody></concept>