Distributed high-performance computing---so-called metacomputing---refers to the coordinated use of a pool of geographically distributed high-performance computers. The user's view of an ideal metacomputer is that of a powerful monolithic virtual machine. The implementor 's view, on the other hand, is that of a variety of interacting services implemented in a scalable and extensible manner. In this paper, we present MOL, the Metacomputer Online environment. In contrast to other metcomputing environments, MOL is not based on specific programming models or tools. It has rather been designed as an open, extensible software system comprising a variety of software modules, each of them specialized in serving one specific task such as resource scheduling, job control, task communication, task migration, user interface, and much more. All of these modules exist and are working. The main challenge in the design of MOL lies in the specification of suitable, generic interfaces for the effective ...

Distributed reference counting is a general purpose technique, which may be used, e.g., to detect termination of distributed programs or to implement distributed garbage collection. We present a distributed reference counting algorithm and a mechanical proof of correctness carried out using the proof assistant Coq. The algorithm is formalised by an abstract machine, and its correctness has two dierent facets. The safety property ensures that if there exists a reference to a resource, then its reference counter will be strictly positive. Liveness guarantees that if all references to a resource are deleted, its reference counter will eventually become null. 1 Introduction Reference counting is a general purpose technique that is able to count the number of references to a given resource. Collins [5] was the rst to use it in order to determine when list cells were no longer needed. Operating systems rely on this technique in order to decide when les may be deleted or when le...

We present a framework for designing parallel programming languages whose semantics is functional and where communications are explicit. To this end, we specialize Brookes and Geva's generalized concrete data structures with a notion of explicit data layout and obtain a CCC of distributed structures called arrays. We find that arrays' symmetric replicated structures, suggested by the data-parallel SPMD paradigm, are incompatible with sum types. We then outline a functional language with explicitly-distributed (monomorphic) concrete types, including higher-order, sum and recursive ones. In this language, programs can be as large as the network and can observe communication events in other programs. Such flexibility is missing from current data-parallel languages and amounts to a fusion with their so-called annotations, directives or meta-languages. 1 Explicit communications and functional programming Faced with the mismatch between parallel programming languages and the requirements o...