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

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

<!-- This component and the accompanying materials are made available under the terms of the License 

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

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

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

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

<concept id="GUID-6408C26A-2736-59A9-B785-6B119143619B" xml:lang="en"><title>How

to use a thread-death notifier</title><shortdesc>Describes the thread-death notifier and provides a code snippet

to show you how to use it.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>To use a thread-death notifier, a thread which needs to know about the

death of other threads: </p>

<ul>

<li id="GUID-914D2BE7-BFD3-58E3-ABD4-53371512332F"><p>constructs an <codeph>RUndertaker</codeph> handle

and then calls its <codeph>Create()</codeph> member function to create the

associated Kernel side object. The <codeph>RUndertaker</codeph> handle is <keyword>process-relative</keyword> which

means that the handle is <i>not</i> closed if the requesting thread dies. </p> </li>

<li id="GUID-F46FEA42-38C3-526D-AC05-225BDD3A8714"><p>issues a notification

request to the thread-death notifier, passing a reference to a <codeph>TRequestStatus</codeph> object

and a reference to a <codeph>TInt</codeph>. </p> </li>

</ul>

<p>When any other thread dies, the requesting thread's <keyword>request semaphore</keyword> is

signalled to indicate that the notification request is complete. The <codeph>TRequestStatus</codeph> object

supplied by the requesting thread is set to <codeph>KErrDied</codeph>. </p>

<p>In addition, the Kernel opens a local thread-relative handle on the dying

thread. (thread-relative, here, means relative to the requesting thread) and

sets the <codeph>TInt</codeph>, supplied by the requesting thread, to the

resulting handle-number. The requesting thread can construct an <codeph>RThread</codeph> from

this handle-number. The following diagram helps visualise the situation. </p>

<fig id="GUID-5B53CA3B-5365-5C54-B2BC-EA8BA684F15E">

<title>           Thread-death notifier         </title>

<image href="GUID-70483E81-311F-5247-9F39-3940F20C0EB1_d0e238861_href.png" placement="inline"/>

</fig>

<p>The following code fragments demonstrate this: </p>

<codeblock id="GUID-B5A219AD-CC59-50CE-A65B-0D3F4FD32F7A" xml:space="preserve">{

...

RUndertaker     the_undertaker;

TRequestStatus  the_status;

TInt            the_dyingthread_handle_number;

...

the_undertaker.Create();

the_undertaker.Logon(the_status,the_dyingthread_handle_number);

User::WaitForRequest(the_status);

...

...// prepare for a long wait

...

RThread r;

r.SetHandle(the_dyingthread_handle_number);

...

...// Now have an open thread-relative handle to the

...// dying thread so we can, for example, ...

if (r.ExitReason()==0x666)

    {

    ...

    }

...// We have an open handle on the dying thread; the dying thread

...// remains in existence until we close it.

r.Close();

...

}</codeblock>

<p>In practical code, an <codeph>RUndertaker</codeph> is used by an active

object. </p>

<p>The <codeph>RUndertaker</codeph> handle also offers a <codeph>LogonCancel()</codeph> function.

Calling this function, causes the requesting thread's <keyword>request semaphore</keyword> to

be signalled and any wait to complete. The <codeph>TRequestStatus</codeph> is

set to <codeph>KErrCancel</codeph>. </p>

<p>This technique of using an <codeph>RUndertaker</codeph> is not guaranteed

to report the death of all threads. In particular, if a second thread dies

while a requesting thread is handling the request completion due to the death

of a first thread (but before it can make another notification request), the

death of this second thread will go unnoticed. </p>