RESOURCES

**This is an old revision of the document!**

Upcoming Talks

Previous years: 2009, 2008, 2007, 2006, 2005

*In chronological order*

- 2010-01-07 - 16:15, BC 355 Jean-Loup Carré

Abstract:

A great variety of static analyses that compute safety properties of single- thread programs have now been developed. I will present a systematic method to extend a class of such static analyses, so that they handle programs with multiple POSIX-style threads. Starting from a pragmatic operational semantics, the final algorithm is then derived by abstract interpretation. It analyses each thread in turn, propagating interferences between threads, in addition to other semantic information. The combinatorial explosion, ensued from the explicit consideration of all interleavings, is thus avoided. The worst case complexity is only increased by a factor n compared to the single-thread case, where n is the number of instructions in the program. This method is implemented in Penjili, an EADS tool, demonstrating the practicality of the approach.

**Links:**

- 2010-01-08 - 11:00, BC 410 Tho T. Quan

Abstract:

Programming skill is crucial for all Computer Science students which can only be mastered through intensive exercise practice. Apart from traditional face-to-face manner of teaching programming, which suffers certain disadvantages when dealing with large-sized classes, Web-based tutoring systems that can play the role of teacher are increasingly considered. With the recent advancement of Internet, such systems can liberate the learners from the restriction of time and venues for practice, as well as significantly reducing the cost of manpower.

To make those ideas feasible and practical, we propose a framework for automatic verification of programming works submitted from students. In our framework, we employ some formal methods for software verification, e.g. theorem proving and model checking, thus avoiding the risk of execution of actual code from student, which may sometimes be harmful. In particular, by the means of model checking, we are able to render the learners with some useful features such as invariant-free checking of loop-based programs or generation of counter-examples associated with error-flows. Our framework has been implemented and employed in our Faculty in the course of Programming Methodologies, and the initial results are somehow promising.

~~ IMPORTANT: this talk will take place in BC410 ~~

- 2010-03-04 - 10:00, BC 355, Boaz Patt-Shamir, Tel Aviv University

Abstract:

We consider a scenario where large data frames are broken into a few packets and transmitted over the network. Our focus is on a bottleneck router: the model assumes that in each time step, a set of packets (a burst) arrives, from which only one packet can be served, and all other packets are lost. A data frame is considered useful only if none of its constituent packets is lost, and otherwise it is worthless. We abstract the problem as a new type of online set packing, present a randomized distributed algorithm and a matching lower bound on the competitive ratio for any randomized online algorithm. Our bounds are expressed in terms of the maximal burst size and the maximal number of packets per frame. We also present refined bounds that depend on the uniformity of these parameters.

Joint work with Emek, Halldorsson, Mansour and Rawitz

- 2010-03-05 - 10:00, BC 355 Didier Buchs, Steve Hostettler, Alexis Maréchal

Abstract:

Algebraic Petri Nets (APN: Petri Nets + Algebraic Abstract Data Types)
are powerful tools to model concurrent systems. Because of their high
expressive power, allowing end-users to model complex systems in a compact
way, state space explosion is a big issue when verifying properties on APN models.
Symbolic Model Checking (SMC) and particularly Decision Diagrams (DD) based model
checking is a proven technique to handle the state space explosion for simpler
formalisms such as P/T Petri nets.
This presentation shows how to use Binary Decision Diagrams' (BDD)
evolutions (Data Decision Diagrams, Set Decision Diagrams, SigmaDD, to
tackle the state space explosion problem in the APN world.
The main contribution of this work is the notion of the *Algebraic
Cluster* and partial net unfolding that tackles the concurrency induced
by token multiplicity.
These algorithms have been implemented in a tool that is freely
accessible on http://alpina.unige.ch, a short demo will be made.

- 2010-03-23 - 16:15, INM 10, Manuel Fähndrich, Microsoft Research

Abstract: Over the last few years Microsoft Research has been working on bringing simple and pragmatic program specification, aka Code Contracts, to programming languages targeting the Microsoft .NET platform. Contracts document programming assumptions in a machine discoverable form.

Contracts are targeted at the general developer, not the verification enthusiast. It is thus important to use a single form of specifications that meets three simultaneous goals:

- First and foremost, contracts serve as documentation. They must be as readable as possible.
- Second, contracts should be executable. This motivates writing specifications for testing and immediate perceived benefit, without consideration of static verification.
- Finally, contracts should help in static defect discovery and reduce false positives.

Our specification approach is language-agnostic in that we use idiomatic code written in the developer's source language to express preconditions, postconditions, and object invariants.

- 2010-03-30 - 12:30-13:15, INR 113, Professor Peter Mueller, ETHZ. Given the time of the talk, light sandwiches and coffee will be served.

Abstract: Closures, first-class citizen procedures that are able to capture their lexical environment, increase the expressiveness of object-oriented languages such as C#, Scala, and various dynamic languages. However, closures make program specification and verification more difficult. For instance, a verification methodology must allow specifications to describe the behavior of one method relatively to the specification of another method passed as argument, and it must allow specifications to describe the behavior of a closure without exposing its captured state. This paper presents a modular specification and verification methodology for closures. Our solution is based on first-order logic and, thus, well suited for automatic verification with SMT solvers. We have verified a series of interesting examples that cover the main applications of closures such as delegation patterns and even the creation of custom control flow.

- 2010-04-13 - 16:15, INM 10, Alain Finkel, ENS de Cachan

**Abstract**: The theory of Well Structured Transition Systems provides the
good structure for computing a finite basis of the set of predecessors
of the upward closure of a finite set of states. We address here the
dual problem which is to compute a finite representation of the set of
successors of the downward closure of a finite set of states (called the
cover). This last problem is, a priori, more difficult because in
general, the cover has no finite basis.
It is possible to complete any well-ordered set to obtain a cpo in which
every downward closed set has a finite representation.
We then define the framework of Complete Well Structured Transition
Systems and we propose a simple and a conceptual procedure for computing
the covering set. This procedure terminates more
often than the generalized Karp-Miller tree procedure when applied on
extended Petri nets and lossy channel systems.

- 2010-04-27 - 16:15, INM 10, David Monniaux, VERIMAG, Grenoble

Abstract: We propose a method for automatically generating abstract transformers for static analysis by abstract interpretation. The method focuses on linear constraints on programs operating on rational, real or floating-point variables and containing linear assignments and tests.

In addition to loop-free code, the same method also applies for obtaining least fixed points as functions of the precondition, which permits the analysis of loops and recursive functions. Our algorithms are based on new quantifier elimination and symbolic manipulation techniques.

Given the specification of an abstract domain, and a program block, our method automatically outputs an implementation of the corresponding abstract transformer. It is thus a form of program transformation.

The motivation of our work is data-flow synchronous programming languages, used for building control-command embedded systems, but it also applies to imperative and functional programming.

- 2010-06-16 - 16:15, INR 331, Philipp Haller, EPFL

Abstract:

An important application of unique object references is safe and efficient message passing in concurrent object-oriented programming. However, to prevent the ill effects of aliasing, practical systems often severely restrict the shape of messages passed by reference. Moreover, the problematic interplay between destructive reads–often used to implement unique references–and temporary aliasing through ``borrowed'' references is exacerbated in a concurrent setting, increasing the potential for unpredictable run-time errors.

This paper introduces a new approach to uniqueness. The idea is to use capabilities for enforcing both at-most-once consumption of unique references, and a flexible notion of uniqueness. The main novelty of our approach is a model of uniqueness and borrowing based on simple, unstructured capabilities. The advantages are: first, it provides simple foundations for uniqueness and borrowing. Second, it can be formalized using a relatively simple type system, for which we provide a complete soundness proof. Third, it avoids common problems involving borrowing and destructive reads, since unique references subsume borrowed references.

We have implemented our type system as an extension to Scala. Practical experience suggests that our system allows type checking real-world actor-based concurrent programs with only a small number of additional type annotations.

- 2010-07-07 - 16:15, INR 113, Prof. Rupak Majumdar

Abstract:

Bounded languages, introduced by Ginsburg and Spanier, are subsets of regular languages of the form w1*w2*… wk* for some words w1,…,wk. Bounded languages have nice structural and decidability properties.

We show two applications of bounded languages in model checking: first, to underapproximate the reachable state space of multithreaded procedural programs and second, to underapproximate the reachable state space of counter machines. In particular, we show that verification with bounded languages generalizes context-bounded reachability for multithreaded programs.

We also show a new and constructive proof of the following language-theoretic result: for every context-free language L, there is a bounded context-free language L' which is a subset of L and has the same Parikh image as L.

(Joint work with Pierre Ganty and Benjamin Monmege)