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version 1.2, 2002/02/07 16:46:42

version 1.3, 2002/03/12 22:57:40

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<html>

<head>

<title>Pegasus Meta Dispatcher</title>

</head>

<body>

<p class="copyright">this is copyright text</p>

<div class="constraint">this is a constraint</div>

<div class="exampleInner"><code>this is an inner example</code></div>

<h1>Pegasus Meta Dispatcher</h1>

<p>

The Pegasus Meta Dispatcher is a set of classes that extend the

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asynchronous, and multithreaded. The primary classes consist of the

folowing:

</p>

<table>

<tr align="left"><th>Class</th><th>Derived from</th><th>Source file</th></tr>

<tr><td>cimom</td><td>MessageQueue</td><td>Pegasus/Common/Cimom.h</td></tr>

<tr><td><div class="exampleInner">cimom</div></td><td>MessageQueue</td><td>Pegasus/Common/Cimom.h</td></tr>

<tr><td>MessageQueueService</td><td>MessageQueue</td><td>Pegasus/Common/MessageQueueServices.h</td></tr>

<tr><td>CimomMessage</td><td>Message</td><td>Pegasus/Common/CimomMessage.h</td></tr>

<tr><td>AsyncOpNode</td><td>n/a</td><td>Pegasus/Common/AsyncOpNode.h</td></tr>

<tr><td>AsyncDQueue</td><td>unlocked_dq</td><td>Pegasus/Common/DQueue.h</td></tr>

<tr><td>IPC classes</td><td>n/a</td><td>Pegasus/Common/IPC.h</td></tr>

<tr><td>Threading classes</td><td>n/a</td><td>Pegasus/Common/Thread.h</td></tr>

</table>

<br>

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The Meta Dispatcher therefore acts as a central message

hub. Services communicate with each other <i>via</i> the Meta

Dispatcher.

<pre>

Service A--Message----1----> (block on semaphore)

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</pre>

</div></div>

The numbered steps above are as follows:

<ol>

<li><b>Service A</b> creates a new <code>AsyncMessage</code> and

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</ol>

<hr>

<h2>Sending Messages without Blocking (Async with Callback)</h2>

<p>

Whenever there is a possibility that the processing of

one message may generate a nested message (message

generated within the handler of a message) it is

necessary to send messages without blocking, and to

receive responses via callback routines. The diagram

below shows the (more complicated) flow of

non-blocking messages.

</p>

<br>

<pre>

Service A--Message----1---->

. <-----------(return)-+----->-(loop)--->-+

. | Meta Dispatcher |

. +----<-----<---<---+

. Message---2-->Service B

. |

. <--Response--3------+

. |

. +--<--<-----<-----+--(return)---->

. | Meta Dispatcher |

Service A <--Callback--4---+--->-(loop)-->---+

| ^

+-------+

</pre>

</div></div>

<h3>Test Program</h3>

<p>

There is a test program that sends and receives

non-blocking messages in

<code>$(PEGASUS_ROOT)/src/Pegasus/Common/tests/async_callback/</code>

</p>

<h3>SendAsync method</h3>

<p>

The <code>MessageQueueService</code> class sends

non-blocking messages using the <code>SendAsync</code>

method from <code>MessageQueueService.h</code>.

</p>

<pre>

Boolean <b><font color=#000000>SendAsync</font></b><font color=#990000>(</font>AsyncOpNode <font color=#990000>*</font>op<font color=#990000>,</font>

Uint32 destination<font color=#990000>,</font>

<font color=#009900>void</font> <font color=#990000>(</font><font color=#990000>*</font>callback<font color=#990000>)</font><font color=#990000>(</font>AsyncOpNode <font color=#990000>*</font><font color=#990000>,</font> MessageQueue <font color=#990000>*</font><font color=#990000>,</font> <font color=#009900>void</font> <font color=#990000>*</font><font color=#990000>)</font><font color=#990000>,</font>

MessageQueue <font color=#990000>*</font>callback_q<font color=#990000>,</font>

<font color=#009900>void</font> <font

color=#990000>*</font>callback_ptr<font color=#990000>)</font><font color=#990000>;</font>

</pre>

<h2>Class Definitions</h2>

<h3>cimom (Meta Dispatcher)</h3>

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<address><a href="mailto:mdday@us.ibm.com">Michael Day</a></address>

Last modified: Thu Feb 7 11:48:22 EST 2002

Last modified: Tue Mar 12 17:48:45 EST 2002

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