Samuel Tardieu

GARLIC: generic Ada reusable library for interpartition communication

This paper presents an implementation of the distributed programming features of Ada 95 within the GNAT system. The work we describe is the result of an international collaboration whose goal is to produce a high level environment for distributed system programming. This paper focuses on issues of interprocessor communication, since this is the core element of our software architecture. We describe the design and implementation of GARLIC, an interface between the network and the application. GARLIC is an extension of the predefined interface specified by System.RPC.

GLADE: a framework for building large object-oriented real-time distributed systems

This paper describes how GLADE, our implementation of the Ada 95 Distributed Systems Annex, can be used to build large object-oriented real-time distributed systems. In addition to the powerful distribution features included in the Ada 95 language itself, we provide extensions to help the programmer build robust and failsafe distributed applications.

CORBA & DSA: Divorce or Marriage?

This paper presents a comparison between CORBA and the Ada 95 Distributed Systems Annex. We also focus on the latest developments made by the ENST research team to GLADE that are related to CORBA services.

Debugging distributed applications with replay capabilities

This paper focuses on the latest developments made by the ENS T research team to GLADE, the implementation of the Distribut ed Systems Annex for the GNAT Ada95 compiler; we have extended GLADE’s communication subsystem and added recording facil ities and replay capabilities. This makes debugging distri buted applications much easier because of the possibility to repl ay separately each partition by simulating external events at consistent dates without loosing the possible determinism of t he original program, and it also eases the debugging in cases wh ere it is not practical to re-run the whole program or when it is im possible to get exactly the same behaviour from one of the par t (for example when one or several parts of the application run on embedded targets and send messages depending on sensor inputs while the other parts run on fixed workstations). 1 Ada95 RM Annex E and GLADE The Ada Distributed Systems Annex, Annex E, provides a solution to programming distributed systems. An Ada applicat ion may be partitioned for execution across a network of compute rs so that typed objects may be referenced through remotely-ca lled subprograms. The remotely-called subprograms declared in a library unit categorized as remote call interface (RCI) may be either statically or dynamically bound, thereby allowing a pplications to use one of these three classical paradigms: Remote procedure call: a remote procedure call 1 is similar for the end-user to a regular procedure call. Arguments are pushed into a stream along with some data pointing out which remote procedure is to be used and the stream is transmitted (maybe after some filtering phase, see [14]) over the network to the other partition. This partition decodes the stream, does the regular subprogram call, then put the output parameters into another stream along with the exception (if any) raised by the subprogram and sends this stream back to the caller. The caller decodes the stream and raises the exception if needed. Also, a pointer on a remote procedure call can be dereferenced to make the remote call occur. Asynchronous procedure call: an asynchronous procedure call is similar to a remote procedure call, but it doesn’t wai t for the completion of the remote call and lets the caller continue its execution path. Of course, this model is applicable to procedure with onlyin parameters and any exception raised during the execution of the remote procedure is lost. Distributed objects: this model, similar to the one adopted in CORBA, defines the notion of remote-pointer, a pointer which designates a remote object (the pointer type is said to be RACW, that is remote access to class-wide type). When a primitive dispatching operation is invoked on an object pointed by a RACW, then the corresponding remote call is performed transparently (if the object was created locally). This very powerful mechanism provides the user with a mean of registering objects into an object server and calling methods of these objects without knowing where they were originally created. An Ada95 distributed application include a number of partitions which can be executed concurrently on the same maIn fact a remote procedure call can well be a remote function c all, so the appropriateterm (notchosen for the ReferenceManual) shou ld have been “Remote

PARIS - Partitioned Ada for Remotely Invoked Services

This paper presents our experience implementing the Ada 95 Annex E to support distributed systems using the GNAT compiler[6]. The work has been performed by a multinational team from France and the USA. The paper describes the implementation of the Partition Communication System and the required support from the GNAT compiler. In addition, extensions beyond Annex E are described that facilitate programming the next generation of distributed applications in Ada 95.

Picolibre: a free collaborative platform to improve students' skills in software engineering

The work described in this paper consists in the development of a pedagogical collaborative platform to improve the know-how of our students in software engineering and collaborative work. Its use in a free software context leads to greater commitment of the students and better reusability of their work. Keywords— Skill development, new information technology tools, project activity, active learning, monitoring, sofware engineering, collaborative work, free software

Building an efficient overlay for publish/subscribe in wireless sensor networks

In this paper we examine how to efficiently build a brokers overlay to implement publish/subscribe in a wireless sensor network, trying to reduce sensor nodes energy consumption, memory required for buffering packets and delivery time. We evaluate, on the connectivity graph that represents the network, the performance of various criteria that can be used to select brokers among the set of nodes. We compare a dominating set approach with the selection of the best ranked brokers based on centrality measures. We finally give hints on how to implement a distributed algorithm to approximate the most efficient overlays.

Publish/subscribe for wireless sensor networks

This extended abstract overviews some of the advantages and problems to overcome when implementing a publish/subscribe system over a wireless sensor network. Publish/subscribe usually relies on a set of intermediate nodes, brokers that gather and dispatch all the packets emissions. The presence of these brokers lightens the duty of most regular nodes, as they are the only ones who really need to know nodes identities and to maintain long-range routes. However, as computing power, memory, energy and channel bandwidth are scarce resources in WSN, defining an efficient brokering architecture is not trivial. After presenting publish/subscribe in a wireless sensor network context, we examine various performance criteria and discuss on the brokering overlay. If a multi-brokers architecture seems necessary to distribute the load across the network, questions such as the correct number of brokers and their location are difficult when taking into account multiple criteria and that brokers need to remain synchronized. The dynamics of the system also requires attention, as brokers may appear or disappear according to the network traffic patterns or to battery levels.

Complementing Ada with other programming languages

This paper presents our experience in using Ada and the Ravenscar profile in a robotics non-profit association and in a robotics competition. While Ada is our primary and dominant language, we have complemented it with a hardware description language (Verilog) and an interactive language (Forth). We describe the interface between those languages, and the design choices that have been made to minimize the risks taken by leaving the Ada world. We also explain why we chose in some conditions to relax restrictions imposed by the use of the Ravenscar profile.