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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>