. Dynamic binding, which has always been associated with Lisp, is still semantically obscure to many. Although largely replaced by lexical scoping, not only does dynamic binding remain an interesting and expressive programming technique in specialised circumstances, but also it is a key notion in semantics. This paper presents a syntactic theory that enables the programmer to perform equational reasoning on programs using dynamic binding. The theory is proved to be sound and complete with respect to derivations allowed on programs in "dynamic-environment passing style". From this theory, we derive a sequential evaluation function in a context-rewriting system. Then, we exhibit the power and usefulness of dynamic binding in two different ways. First, we prove that dynamic binding adds expressiveness to a purely functional language. Second, we show that dynamic binding is an essential notion in semantics that can be used to define the semantics of exceptions. Afterwards, we further refin...

We introduce a new lambda calculus with futures, λ(fut), to model the operational semantics of concurrent extensions of ML. λ(fut) can safely express a variety of high-level concurrency constructs, including channels, semaphores, or ports. Safe implementations of these constructs in (fut) cannot be corrupted in any well-typed context. We prove safety on basis of a linear type system.

Speculative evaluation, including leniency and futures, is often used to produce high degrees of parallelism. Existing speculative implementations, however, may serialize computation because of their implementation of queues of suspended threads. We give a provably efficient parallel implementation of a speculative functional language on various machine models. The implementation includes proper parallelization of the necessary queuing operations on suspended threads. Our target machine models are a butterfly network, hypercube, and PRAM. To prove the efficiency of our implementation, we provide a cost model using a profiling semantics and relate the cost model to implementations on the parallel machine models. 1 Introduction Futures, lenient languages, and several implementations of graph reduction for lazy languages all use speculative evaluation (call-by-speculation [15]) to expose parallelism. The basic idea of speculative evaluation, in this context, is that the evaluation of a...

The Task Parallel Library (TPL) is a library for.NET that makes it easy to expose potential parallelism in a program. The library can be seen as an embedded domain specific language, and relies heavily on generics and delegate expressions to provide a convenient interface with custom control structures for parallelism. In this article, we describe the design and implementation of the library. In particular, we show the use of ‘replicable tasks ’ as an abstraction for implementing parallel iteration and aggregation, and the use of ‘duplicating queues ’ as an alternative to the regular task queues based on the THE protocol. 1.

This paper describes the semantics of Quantum, a language that was specifically designed to control resource consumption of distributed computations, such as mobile agent style applications. In Quantum, computations can be driven by mastering their resource consumption. Resources can be understood as processors cycles, geographical expansion, bandwidth or duration of communications, etc. We adopt a generic view by saying that computations need energy to be performed. Quantum relies on three new primitives that deal with energy. The first primitive creates a tank of energy associated with a computation. Asynchronous notifications inform the user of energy exhaustion and computation termination. The other two primitives allow us to implement suspension and resumption of computations by emptying a tank and by supplying more energy to a tank. The semantics takes the form of an abstract machine with explicit parallelism and energy-related primitives. 1 Introduction Millions of computers ...

We propose a high-level approach to program distributed applications; it is based on the annotation future by which the programmer specifies which expressions may be evaluated remotely in parallel. We present the CEKDS-Machine, an abstract machine with a distributed memory, able to evaluate Schemelike future-based programs. In this paper, we focus on the issue of task migration and prove that task migration is transparent to the user, i.e. task migration does not change the observable behaviour of programs. 1 Introduction Distributed systems are omnipresent: local area networks and the explosion of the Internet in the past years are particular illustrations of the ubiquity of distributed computing. A major research focus in this area has been the design of new languages or programming paradigms to develop distributed applications, like for instance PVM [8], MPI [6], Nexus [7], Cilk [1]. We argue that those systems were designed in the perspective of building high-performance distrib...

Millions of computers are now connected together by the Internet. At a fast pace, applications are taking advantage of these new capabilities, and are becoming parallel and distributed, e.g. applets on the WWW or agent technology. As we live in a world with finite resources, an important challenge is to be able to control computations in such an environment. For instance, a user might like to suspend a computation because another one seems to be more promising. In this paper, we present a paradigm that allows the programmer to monitor and control computations, whether parallel or distributed, by mastering their resource consumption. We describe an implementation on top of the thread library PPCR and the message-passing library Nexus. 1 Introduction As we live in a world with finite resources, it is of paramount importance for the user to be able to monitor and control computations. This task is all the more complex since computations may be parallel, distributed, and most probably ma...

. Coordination languages for parallel and distributed systems specify mechanisms for creating tasks and communicating data among them. These languages typically assume that (a) once a task begins execution on some processor, it will remain resident on that processor throughout its lifetime, and (b) communicating shared data among tasks is through some form of message-passing and data migration. In this paper, we investigate an alternative approach to understanding coordination. Communication-passing style (CmPS) refers to a coordination semantics in which data communication is always undertaken by migrating the continuation of the task requiring the data to the processor where the data resides. Communication-passing style is closely related to continuation-passing style (CPS), a useful transformation for compiling functional languages. Just as CPS eliminates implicit call-return sequences, CmPS eliminates implicit inter-processor data communication and synchronization requests. In a C...

Enabling applications to execute various tasks in parallel is difficult if those tasks exhibit read and write conflicts. We recently developed a programming model based on concurrent revisions that addresses this challenge in a novel way: each forked task gets a conceptual copy of all the shared state, and state changes are integrated only when tasks are joined, at which time write-write conflicts are deterministically resolved. In this paper, we study the precise semantics of this model, in particular its guarantees for determinacy and consistency. First, we introduce a revision calculus that concisely captures the programming model. Despite allowing concurrent execution and locally nondeterministic scheduling, we prove that the calculus is confluent and guarantees determinacy. We show that the consistency guarantees of our calculus are a logical extension of snapshot isolation with support for conflict resolution and nesting. Moreover, we discuss how custom merge functions can provide stronger guarantees for particular data types that are tailored to the needs of the application. Finally, we show we can visualize the nonlinear history of state in our computations using revision diagrams that clarify the synchronization between tasks and allow local reasoning about state updates. CR-number [sub-

. Coordination languages for parallel and distributed systems specify mechanisms for creating tasks and communicating data among them. These languages typically assume that (a) once a task begins execution on some processor, it will remain resident on that processor throughout its lifetime, and (b) communicating shared data among tasks is through some form of message-passing and data migration. In this paper, we investigate an alternative approach to understanding coordination. Communication-passing style (CmPS) refers to a coordination semantics in which data communication is always undertaken by migrating the continuation of the task requiring the data to the processor where the data resides. Communication-passing style is closely related to continuation-passing style (CPS), a useful transformation for compiling functional languages. Just as CPS eliminates implicit call-return sequences, CmPS eliminates implicit inter-processor data communication and synchronization reque...