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<concept id="GUID-C21BB0E4-7AF7-58E5-AAD6-8CE67399460C" xml:lang="en"><title>MessageQueue Example</title><shortdesc>This example application shows the use of message queue
in interprocess communication using the RMsgQueue class.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section id="GUID-ED679CA7-FF4C-4E69-8663-5DA46A3D94F4"><title>Download</title> <p>Click on the following link to download the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-d72e85ad-4659-4f66-9cb3-f084e9505709.zip" scope="external">MessageQueueExample.zip</xref>.</p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-d72e85ad-4659-4f66-9cb3-f084e9505709.html" scope="peer">browse</xref> to view the example code.</p> </section>
<section id="GUID-39D2064D-AD24-4785-956F-18A0CAD57B81"><title>Description</title> <p>The example describes the global message queue. The following
sections provide more information. </p> <p><b> MessageQueueExample</b> </p> <p>The example comprises two processes: a Collector, which
collects words from the user via the console, and an Inverter, which
periodically reverses the order of the collected words. The Collector
and the Inverter pass words to each other using two message queues:
InverterInQ and InverterOutQ. The Collector is the main process which
starts the Inverter process. The Collector process takes user input
in form of different words and sends to the Inverter process via message
queue. The Inverter process receives messages at a regular interval
of 10 seconds, inverts the words in the message and sends it back
to the Collector. </p> <p>The Collector creates an active object to
collect words from the user and another active object to receive words
from the Inverter. Each active object has its own console for display.
More information about running the example is given in the build section
of this document. </p> <p><b>Design</b> </p> <p>The following block
diagram describes the example in more detail. </p> <fig id="GUID-27A0C389-EDDD-5E17-82EE-2727F21803AF">
<image href="GUID-CD7F507C-CDD5-5612-BA1B-72641D28FA4A_d0e254198_href.png" placement="inline"/>
</fig><p><filepath>CCollector.exe</filepath> is the Collector process.
The user starts the Collector and creates an active scheduler and
two global message queues. It also starts the Inverter process called <filepath>Inverter.exe</filepath>. The Collector creates one active object
to collect words from the user and another active object to monitor
its input queue (InverterOutQ). The active object to collect words
is an object of class CCollector and the active object which monitors <codeph>InverterOutQ</codeph> is an object of class <xref href="GUID-A39BC295-2845-3018-B8B8-49418277E7EB.dita"><apiname>CMsgQActive</apiname></xref>. The two active objects have different consoles (one for user input
and one for displaying the output message). </p><p> The user inputs
words in the console. The set of words goes to the <codeph>InverterInQ</codeph> when the "<codeph>Enter</codeph>" key is pressed. If the "<codeph>ESC</codeph>" key is pressed, the system stops and sends the command
to the Inverter process to stop.</p><p> The Inverter is another process
which opens the global message queues. It creates an active scheduler
and implements a periodic timer. The timer wakes every 10 seconds
to receive the words from the <codeph>InverterInQ</codeph>. It also
checks for a stop command, which closes the message queue and the
two process. The Inverter inverts the received words and sends the
result to <codeph>InverterOutQ</codeph>. </p><p>In the Collector process,
the active object that monitors the <codeph>InveterOutQ</codeph> opens
the message queue, receives the received words and displays  them
in its console. It uses the <xref href="GUID-22E24B08-175B-3446-9D48-9AC4B1663E35.dita"><apiname>NotifyDataAvailable(TRequestStatus&amp;)</apiname></xref> API to monitor the queue for the next set of data. </p><p>The Class diagram of the example is shown below </p><fig id="GUID-E93EF1D6-1B9D-4C76-80B0-1FF660B5C75A">
<image href="GUID-3560E862-CB68-584F-B9B6-FCD9F0D202DC_d0e254247_href.png" placement="inline"/>
</fig> </section>
<section id="GUID-86B04D06-7046-49BD-AE1A-57D5E406F864"><title>Class
summary</title><ul>
<li><p> <xref href="GUID-3CECC9FC-58C1-3117-AAF2-FDF88341F56F.dita"><apiname>CPeriodic</apiname></xref> - Periodic timer active object.</p></li>
<li><p><xref href="GUID-5195B8D1-851E-3BEE-A72D-1841C0937300.dita"><apiname> RMsgQueue</apiname></xref> - A handle to a message queue.</p></li>
<li><p><xref href="GUID-9DD1EA2B-DC59-315C-8E9C-CE6D9461B695.dita"><apiname> RProcess </apiname></xref> - A handle to a process.</p></li>
<li><p><xref href="GUID-067293BF-B28C-3CEC-92F4-1351A795EA7F.dita"><apiname> CActive</apiname></xref> - The core class of the active
object abstraction.</p></li>
</ul></section>
<section id="GUID-F8D41313-760D-417E-834C-09D41F4EDB06"><title>Build</title> <p>The <xref href="GUID-3100800B-B2F7-50EF-BD4C-3C345ECCB2A5.dita">Symbian
build process</xref> describes how to build this example application. </p> <p>The example builds an executable called <filepath>Inverter.exe</filepath> and <filepath>Collector.exe</filepath> in the standard locations. </p> <p>To run the example, first build <filepath>Inverter.exe</filepath> and start <filepath>Collector.exe</filepath> from the file system
or from your IDE. After launching the .exes (and depending on the
emulator you are using) you may need to navigate away from the application
launcher or shell screen to view the console. </p> <p>A message input
console is used for user input and an output message console is used
to display inverted words. The output message console that is displayed
at startup. The user can switch between two consoles by <cmdname>Ctrl+Shift+Alt+t </cmdname> combination. </p> <p>The input message console is used to input
words. A user presses enter to send the words to the Inverter and
presses <cmdname>ESC</cmdname> to exit the application. When a user
presses "Enter" the words go to the <codeph>InverterInQ</codeph>.
The Inverter opens the <codeph>InverterInQ</codeph> at periodic intervals
of 10 secs and inverts the words which it sends to the collector via <codeph>InverterOutQ</codeph>. The Collector opens the <codeph>InverterOutQ</codeph> and display the words in the output message console. </p> </section>
</conbody></concept>