Abstract
Automatic grading based on unit tests is a key feature of massive open online courses (MOOC) on programming, as it allows instant feedback to students and enables courses to scale up. This technique works well for sequential programs, by checking outputs against a sample of inputs, but unfortunately it is not adequate for detecting races and deadlocks, which precludes its use for concurrent programming, a key subject in parallel and distributed computing courses. In this paper we provide a hands-on evaluation of verification and testing tools for concurrent programs, collecting a precise set of requirements, and describing to what extent they can or can not be used for this purpose. Our conclusion is that automatic grading of concurrent programming exercises remains an open challenge.

Abstract
A Bloom Filter is a probabilistic data structure designed to check, rapidly and memory-efficiently, whether an element is present in a set. It has been vastly used in various computing areas and several variants, allowing deletions, dynamic sets and working with sliding windows, have surfaced over the years. When summarizing data streams, it becomes relevant to identify the more recent elements in the stream. However, most of the sliding window schemes consider the most recent items of a data stream without considering time as a factor. While this allows, e.g., storing the most recent 10000 elements, it does not easily translate into storing elements received in the last 60 seconds, unless the insertion rate is stable and known in advance. In this paper, we present the Time-limited Bloom Filter, a new BF-based approach that can save information of a given time period and correctly identify it as present when queried, while also being able to retire data when it becomes stale. The approach supports variable insertion rates while striving to keep a target false positive rate. We also make available a reference implementation of the data structure as a Redis module.

Abstract
Current data abstraction mechanisms are not adequate to control sharing of state in the general case involving objects in linked structures. The pervading possibility of sharing is a source of errors and an obstacle to language implementation techniques. We present a general extension to programming languages which makes the ability to share state a first class property of a data type, resolving a long-standing flaw in existing data abstraction mechanisms. Balloon types enforce a strong form of encapsulation: no state reachable (directly or transitively) by a balloon object is referenced by any external object. Syntactic simplicity is achieved by relying on a non-trivial static analysis as the checking mechanism. Balloon types are applicable in a wide range of areas such as program transformation, memory management and distributed systems. They are the key to obtaining self-contained composite objects, truly opaque data abstractions and value types-important concepts for the development of large scale, provably correct programs. © Springer-Verlag Berhn Heidelberg 1997.

Abstract
This chapter contains summaries of the presentations given at the Intercontinental Workshop on Aliasjng in Object-Oriented Systems (IWAOOS'99) at the European Conference on Object-Oriented Programming (ECOOP'99) which was held in Lisbon, Portugal on June 15, 1999.

Abstract
Current data abstraction mechanisms are not adequate to control sharing of state in the general case involving objects in linked structures. The pervading possibility of sharing is a source of errors and an obstacle to language implementation techniques. Balloon types, which we have introduced in [2], are a general extension to programming languages. They make the ability to share state a first class property of a data type. The balloon invariant expresses a strong form of encapsulation: no state reachable (directly or transitively) by a balloon object is referenced by any external object. In this paper we describe the checking mechanism for balloon types. It relies on a non-trivial static analysis, described as an abstract interpretation. Here we focus in particular on the design of the abstract domain which allows the checking mechanism to work under realistic assumptions regarding possible object aliasing. ©1999 Published by Elsevier Science B. V.

Abstract
Determining the size of a network and its diameter are important functions in distributed systems, as there are a number of algorithms which rely on such parameters, or at least on estimates of those values. The Extrema Propagation technique allows the estimation of the size of a network in a fast, distributed and fault tolerant manner. The technique was previously studied in a simulation setting where rounds advance synchronously and where there is no message loss. This work presents two main contributions. The first, is the study of the Extrema Propagation technique under asynchronous rounds and integrated in the Network Friendly Epidemic Multicast (NeEM) framework. The second, is the evaluation of a diameter estimation technique associated with the Extrema Propagation. This study also presents a small enhancement to the Extrema Propagation in terms of communication cost and points out some other possible enhancements. Results show that there is a clear trade-off between time and communication that must be considered when configuring the protocol-a faster convergence time implies a higher communication cost Results also show that its possible to reduce the total communication cost by more than 18% using a simple approach. The diameter estimation technique is shown to have a relative error of less than 10% even when using a small sample of nodes.