StéphaneChatty

chatty@cena.fr

April 13, 1999 1999 Centre d'Études de la Navigation Aérienne This document is a programmer's guide that describes how to use the Ivy Perl library to connect applications to an Ivy bus. This guide describes version 3.0 of the library. The Ivy Perl library was mainly written by Alexandre Bustico from CENA, but this documentation is maintained by users of the library. This document was written in SGML according to the DocBook DTD, so as to be able to generate PDF and html output. However, the authors have not yet mastered the intricacies of SGML, the DocBook DTD, the DocBook Stylesheets and the related tools, which have achieved the glorious feat of being far more complex than LaTeX and Microsoft Word combined together. This explains why this document, in addition to being incomplete, is so ugly. We'll try and improve it. Ivy is a software bus designed at CENA (France). A software bus is a system that allows software applications to exchange information with the illusion of broadcasting that information, selection being performed by the receiving applications. Using a software bus is very similar to dealing with events in a graphical toolkit: on one side, messages are emitted without caring about who will handle them, and on the other side, one decide to handle the messages that have a certain type or follow a certain pattern. Software buses are mainly aimed at facilitating the rapid development of new agents, and at managing a dynamic collection of agents on the bus: agents show up, emit messages and receive some, then leave the bus without blocking the others. As opposed to other software buses, Ivy does not depend on a centralised server. Actually, Ivy is mostly a communication convention between processes, implemented through a collection of libraries in several languages. From the programmer's point of view, Ivy is an information broadcasting channel. The main functions are:

• connecting to a bus. Example: Ivy::start (-loopMode => 'local', -ivyBus => '2011', -appName => "toto" );
• sending a message. Example: Ivy::sendMsgs ("HELLO WORLD")
• bind a message pattern to a callback function. Example: Ivy::bindRegexp ("^HELLO (.*)", [\&cb])
• the main loop. MainLoop

Ivy's decentralised connection scheme probably incurs limitations in terms of how many applications can be connected to an Ivy bus, but this simplifies management a lot. Basically, an Ivy bus is just a set of applications that decide to communicate together. The only conventions between these applications are:

1. the use of the Ivy protocol (for obvious reasons)
2. a bus address, made of a broadcast port number (a bit like a citizen band channel) and a set of networks addresses

When an application wants to connect to a bus, it sends a broadcast message on the networks specified in the bus address, so that all applications present on those networks and listening on the specified port number connect to it. It then becomes part of the bus, and listens like the other ones. The messages are exchanged in text format, and bindings are based on regular expressions with captures. If an application subscribes to HELLO (.*) and if another application emits the message HELLO WORLD, a callback will be called in the first application with WORLD as an argument. You can use Ivy through applications that have been provided to you. This is the case for ivyprobe, an Ivy agent that allows you to examine the messages exchanged on a given bus and to send messages on that bus. You can refer to the web site http://www.tls.cena.fr/products/ivy/ for a list of available agents. However, what you will usually want to do is to develop your own applications. In order to do that you can use an Ivy connection kit, that is a library that implements Ivy. Libraries that implement Ivy are available in the following environments:

• in C on Unix and Windows platforms, with its own communication library
• in C++ on Windows platforms
• in C++ on Unix platforms, integrated with the Uch communication library
• in C++ on Unix platforms, integrated with OpenInventor
• in C++ on Macintosh
• in Perl and in Perl/Tk
• integrated with Object Caml on Unix platforms
• in Scheme on Unix platforms
• in Java

Connecting your application to an Ivy bus just consists in choosing the appropriate library, add the appropriate message emission and reception calls to your code, use the main loop provided in the library or make the necessary integrations, and get your code running! The Ivy Perl library (aka Perl-Net-Ivy or ivy-perl) is a Perl library that allows you to connect applications to an Ivy bus. You can use it to write applications in Perl or any other language that supports Perl extensions (Perl/Tk for instance). This guide documents how you can do that. The Ivy Perl library is known to compile and work in WindowsNT and Linux environments. It should be easy to use on most Posix environments. The Ivy Perl library was originally developed by Alexandre Bustico at CENA. It is maintained by the CENA-Toulouse team. You can get the latest versions of the Ivy C library from CENA (http://www.tls.cena.fr/products/ivy/). Depending on whether you use a supported binary distribution, you can retrieve RPM or Debian packages for Linux (do not forget to get the development package as well as the run-time package), or retrieve the source files and install them by hand. If your packages are Linux/RPM, you have to use the command rpm -i package-name. If your system is Linux/Debian, you have to use the command dpkg -i package-name. Initializing an Ivy agent with the Ivy-Perl library is done by calling function Ivy::start. In theory, initialization is then over. However in practice, as for any asynchronous communication or interaction library, nothing happens until your application has reached the main loop. The Ivy Perl library provides two kind of main loop: a "LOCAL" loop for perl code, and a "TK" loop for perl-Tk code. Here is more details on Ivy::start function: Ivy::start(-loopMode => 'TK', -ivyBus => '2011', -appName => "TOTO", -neededApp => "TITI", -statusFunc => \&statusScan); initializes and connects your application to the bus specified in ivyBus. The string provided should follow the convention described in section XX. Example: "127:2010".. MainLoop; makes your application enter the main loop in which it will handle asynchronous communications and signals. Ivy::stop (); makes your application exit the main loop. Emitting a message on an Ivy bus is much like printing a message on the standard output. However, do not forget that your message will not be emitted if Ivy has not been properly initialized and if you do not have a main loop of some sort running. To emit a message, use IvySendMsg, which works like printf: Ivy::sendMsg ("..."); sends a message on the bus. Subscribing to messages consists in binding a callback function to a message pattern. Patterns are described by regular expressions with captures. When a message matching the regular expression is detected on the bus, the callback function is called. The captures (ie the bits of the message that match the parts of regular expression delimited by brackets) are passed to the callback function much like options are passed to main. Use function Ivy::bindRegexp to bind a callback to a pattern. Ivy::bindRegexp ("^HELLO WORLD", [\&Start]); binds callback function Start to the regular expression specified by regex_format. Ivy::bindRegexp ("^HELLO WORLD", NULL); deletes the binding. By default, the bus used is 127.255.255.255:2010 ie the application will be connected on the port 2010 of the local machine it runs on. You can set the bus to be used by setting the environment variable IVYBUS or by implementing the option -b in the application. The syntax of the messages exchanged is totally free. However, the following convention is recommended:

The message syntax is Subject Attributes

A Subject is an object, named in a hierarchical form: ObjectClass1:object1.ObjectClass2:object2...

Attributes are pairs (attribute-name, value)

Example: AIRCRAFT:LIB720 Moved lat=46.1697 lon=2.0844 vx=-36 vy=-463 afl=330 rate=0 heading=184 ground_speed=465 mach_speed=0 tendance=0 time=24600 Version 3 is only compatible with perl-tk 402-004. It does not work with perl-tk 400.202 (fileId event problem) It does not work with perl-tk_800.011 (remove file descriptor problem)