1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

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     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-F367F6C9-66F7-4061-81A7-0C845D8F39C4" xml:lang="en"><title>Cancellation

    13 of Asynchronous Requests</title><shortdesc>This document describes how a device driver cancels an asynchronous

    14 request.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>Any outstanding asynchronous request can be cancelled. <xref href="GUID-675860FB-AA37-3467-AF52-7D1B17FEE0A6.dita"><apiname>DoCancel()</apiname></xref> is

    16 implemented to handle cancel requests. Cancel requests are either explicitly

    17 made by the user or made when there is a close message. Any pending requests

    18 and queued DFCs are cancelled and the request is completed with <xref href="GUID-6F4A88DA-F54E-3848-9C32-942D6F5F4F3E.dita"><apiname>KErrCancel</apiname></xref>. </p>

    19 <codeblock id="GUID-AEE32663-E6E2-50CC-A756-10CAC0CA503D" xml:space="preserve">/** 

    20  Cancel Asynchronous Requests. This is called from HandleMsg() to 

    21  cancel pending asynchronous requests. This function determines which    

    22  operation is to be cancelled and tidies up the resources specific to 

    23  the request being cancelled, any outstanding DFCs, and timers, and   

    24  signals the client that the operation is completed.

    25  

    26  @param aMask

    27  Mask containing the request number that has to be cancelled 

    28  */

    29 void DExDriverLogicalChannel::DoCancel(TUint aMask)

    30     {

    31     ...

    32     // Any pending asynchronous operation can be 

    33     // cancelled. Check a valid asynchronous request 

    34     // to cancel has been specified.

    35     //

    36     if(aMask&(1<<RExDriverChannel::ERequestTransmitData))

    37         {

    38         if (iTxDataStatus)

    39             {

    40             // If it is a Transmit request, cancel the Transmit DFC. 

    41             // TDfc::Cancel() cancels the DFC if it is already 

    42             // queued. It does nothing if the DFC is not queued.

    43             //

    44             iTxDfc.Cancel();

    45 

    46             // Notify the client (iClient) that the request is 

    47             // completed. The TRequestStatus object is updated with the 

    48             // status and the completion code is provided to the

    49             // client. KErrCancel indicates that the request has been 

    50             // cancelled. Typically, a client thread, waiting on 

    51             // User::WaitForRequest(TRequestStatus &aStatus) or using

    52             // the active object framework, is unblocked and notified. 

    53             // Then the client may read the request status from the 

    54             // TRequestStatus object. 

    55             //                                              

    56             Kern::RequestComplete(iClient,iTxDataStatus,KErrCancel);

    57             }

    58         }

    59     ...

    60     }</codeblock>

    61 </conbody></concept>