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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_d0e346369_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-6E6B3CD0-FB61-336D-9357-2FFBE3F7A57A.dita"><apiname>NotifyDataAvailable()</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_d0e346417_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

OS 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>