MessageQueue +Example

Download

Click +on the following link to download the example: MessageQueueExample.zip.

Click: browse to view the example code.

Description

The +example describes the global message queue. The following sections provide +more information.

MessageQueueExample

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.

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.

Design

The following +block diagram describes the example in more detail.

+ +

CCollector.exe 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 Inverter.exe. +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 InverterOutQ is an object of class CMsgQActive. +The two active objects have different consoles (one for user input and one +for displaying the output message).

The user inputs words in the console. +The set of words goes to the InverterInQ when the "Enter" +key is pressed. If the "ESC" key is pressed, the system stops +and sends the command to the Inverter process to stop.

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 InverterInQ. 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 InverterOutQ.

In +the Collector process, the active object that monitors the InveterOutQ opens +the message queue, receives the received words and displays them in its console. +It uses the NotifyDataAvailable() API to monitor the queue +for the next set of data.

The Class diagram of the example is shown +below

+ +

Class summary

CPeriodic - Periodic timer active object.
RMsgQueue - A handle to a message queue.
RProcessA handle to a process.
CActive - The core class of the active object abstraction.

Build

The Symbian build +process describes how to build this example application.

The +example builds an executable called Inverter.exe and Collector.exe in +the standard locations.

To run the example, first build Inverter.exe and +start Collector.exe 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.

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 Ctrl+Shift+Alt+t combination.

The +input message console is used to input words. A user presses enter to send +the words to the Inverter and presses ESC to exit the application. +When a user presses "Enter" the words go to the InverterInQ. +The Inverter opens the InverterInQ at periodic intervals +of 10 secs and inverts the words which it sends to the collector via InverterOutQ. +The Collector opens the InverterOutQ and display the words +in the output message console.