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<concept id="GUID-E6D9F8CA-F293-5CE6-93C4-5FEC5EBCB2E9" xml:lang="en"><title>Asynchronous
service provider's responsibilities</title><shortdesc>This document describes the functionality required from an asynchronous
service provider.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>An asynchronous service provider must interact in the following ways with
its clients:</p>
<ul>
<li id="GUID-C140D0C8-0486-5AEF-8AFC-732B34078705"><p>prior to initiating
a request, a request function must set the value of the passed <codeph>TRequestStatus</codeph> to <codeph>KRequestPending</codeph>,
which indicates that a request has been issued but not completed.</p> </li>
<li id="GUID-117EE3F9-A2A9-59FE-ABE2-D8CC9C5856C5"><p>requests must be completed
by signalling the requesting thread’s request semaphore by calling <codeph>RThread::RequestComplete()</codeph> with
the <codeph>TRequestStatus</codeph> as the first parameter and the completion
code as the second parameter (which is placed in the <codeph>TRequestStatus</codeph>).</p> </li>
<li id="GUID-EBD83E91-B71C-5532-8EB6-F44541D2DC53"><p>there must be a <i>cancel
function</i> which can cancel an outstanding request. In some cases, calling
the cancel function does not cause cancellation because the request is already
complete. In all cases, the request must be complete before the cancel function
returns.</p> </li>
<li id="GUID-6F7F7419-9170-50C3-AF76-8F03E4FF43D3"><p>if an asynchronous request
is made, it must complete precisely once, whether normally, abnormally, or
through cancellation.</p> </li>
<li id="GUID-DCC53064-2B63-5532-B2E7-3A48FB9CD630"><p>completion through cancellation
is often indicated by a <codeph>TRequestStatus</codeph> code of <codeph>KErrCancel</codeph>.</p> </li>
</ul>
<section id="GUID-08111F39-8412-40CC-B21D-C97A14B43BF8"><title>See also</title> <p><xref href="GUID-E0B34F3E-D4C4-3232-B8B1-7DB35B454646.dita"><apiname>TRequestStatus</apiname></xref> </p> </section>
</conbody></concept>