In stream processing, managing sensitive information in a timely manner while ensuring trust remains a significant challenge. When parties without a priori trust cooperate to execute a streaming application, it is difficult to ensure that sensitive data is kept confidential while guaranteeing that every party executes their code honestly.

Programmers 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 Java, cater to this need by supporting different concurrency models. However, existing programming languages often combine concurrency models in an ad hoc way, and the semantics of the combinations are not always well defined. This article studies the combination of three concurrency models: futures, transactions, and actors. We show that a naive combination of these models invalidates the guarantees they normally provide, thereby breaking the assumptions of programmers. Hence, we present Chocola : a unified language of futures, transactions, and actors that maintains the guarantees of all three models wherever possible, even when they are combined. We describe and formalize the semantics of this language and prove the guarantees it provides. We also provide an implementation as an extension of Clojure and demonstrated that it can improve the performance of three benchmark applications for relatively little effort from the developer.

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.

Many programming languages, such as Clojure, Scala, and Haskell, support different concurrency models. In practice these models are often combined, however the semantics of the combinations are not always well-defined. In this paper, we study the combination of futures and Software Transactional Memory. Currently, futures created within a transaction cannot access the transactional state safely, violating the serializability of the transactions and leading to undesired behavior. We define transactional tasks: a construct that allows futures to be created in transactions. Transactional tasks allow the parallelism in a transaction to be exploited, while providing safe access to the state of their encapsulating transaction. We show that transactional tasks have several useful properties: they are coordinated, they maintain serializability, and they do not introduce non-determinism. As such, transactional tasks combine futures and Software Transactional Memory, allowing the potential parallelism of a program to be fully exploited, while preserving the properties of the separate models where possible.