In the past decades, many different programming models for managing concurrency in applications have been proposed, such as the actor model, Communicating Sequential Processes, and Software Transactional Memory. The ubiquity of multi-core processors has made harnessing concurrency even more important. We observe that modern languages, such as Scala, Clojure, or F#, provide not one, but multiple concurrency models that help developers manage concurrency. Large end-user applications are rarely built using just a single concurrency model. Programmers need to manage a responsive UI, deal with file or network I/O, asynchronous workflows, and shared resources. Different concurrency models facilitate different requirements. This raises the issue of how these concurrency models interact, and whether they are composable. After all, combining different concurrency models may lead to subtle bugs or inconsistencies.In this paper, we perform an in-depth study of the concurrency abstractions provided by the Clojure language. We study all pairwise combinations of the abstractions, noting which ones compose without issues, and which do not. We make an attempt to abstract from the specifics of Clojure, identifying the general properties of concurrency models that facilitate or hinder composition.
Multiple inheritance is often criticised for the ambiguity that arises when multiple parents want to pass on a feature with the same name to their offspring. A survey of programming languages reveals that no programming language has an inherently implicit and dynamic approach to resolve this ambiguity. This paper identifies just-in-time inheritance as the first implicit and dynamic inheritance mechanism. The key idea of just-in-time inheritance is that one of the parents is favoured over the others, which resolves the ambiguity, and that the favoured parent can change at runtime. However, just-in-time inheritance is not the silver bullet to solve all ambiguity problems heir to multiple inheritance, because it is not applicable in all scenarios. We conclude that the applicability of just-in-time inheritance is to be found in systems where multiple inheritance is used to model an ``is-a OR is-a''-relation, rather than the more traditional ``is-a AND is-a''-relation.
Developers often combine different concurrency models in a single program, in each part of the program using the model that fits best. Many programming languages, such as Clojure, Scala, and Haskell, cater to this need by supporting different concurrency models. However, they are often combined in an ad hoc way and the semantics of the combination is not always well defined.This paper studies the combination of three concurrency models: futures, actors, and transactions. We show that a naive combination of these models invalidates the guarantees they normally provide, thereby breaking the assumptions of developers. Hence, we present Chocola: a unified framework of futures, actors, and transactions that maintains the guarantees of all models wherever possible, even when they are combined. We present the semantics of this model and its implementation in Clojure, and have evaluated its performance and expressivity using three benchmark applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.