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<concept id="GUID-8255A186-C1AC-44DA-844C-1FEA029C73BC" xml:lang="en"><title>Publish and Subscribe</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<p><i>Publish and Subscribe</i> has replaced System Agent and the
usage of temporary Shared Data keys.</p>
<p>Publish and Subscribe allows the setting, retrieving and monitoring
of system-wide variables and provides a new inter process communication
(IPC) mechanism for peer to peer communication between threads. Threads
may have the role of the publisher or of the subscriber, while any
thread can define the property to be published. The process that defines
a property can specify access rights for both reading and writing.
Rights can be defined in terms of either requiring a particular <xref href="GUID-6971B0A2-F79B-4E05-8AF3-BB1FC1932A22.dita">capability</xref>, by a process <xref href="GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98.dita#GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98/GUID-EEC50FC0-46D5-4ED7-AD95-67430D5EC652">Secure Identifier</xref>, or by a process <xref href="GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98.dita#GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98/GUID-EEC50FC0-46D5-4ED7-AD95-67430D5EC654">VID</xref>. </p>
<p>Publish and Subscribe should be considered under any of the
following conditions:</p>
<ul>
<li><p>An event should be sent simultaneously to multiple
places over the system.</p></li>
<li><p>Only the last value of the property is significant,
not the intermediate values.</p></li>
<li><p>The source of the value is not significant. The value
may have been set by any publisher with proper rights.</p>
</li>
</ul>
<p>For more information about the use of Publish and Subscribe,
see <xref href="GUID-FE910347-7CC1-5241-B443-88AD3F5A96EF.dita">Using Publish
and Subscribe</xref>.</p>
</conbody></concept>