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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">

</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

</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>

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>