Applications that need to be updated but cannot be easily restarted must be updated at run-time. We evaluate the reflective facilities of Smalltalk with respect to dynamic software and the state-of-the-art in this field. We conclude that while fine for debugging, the existing reflective facilities are not appropriate for dynamically updating production systems under constant load. We propose to enable dynamic updates by introducing first-class contexts as a mechanism to allow multiple versions of objects to coexist. Object states can be dynamically migrated from one context to another, and can be kept in sync with the help of bidirectional transformations. We demonstrate our approach with ActiveContext, an extension of Smalltalk with first-class contexts. ActiveContext eliminates the need for a system to be quiescent for it to be updated. ActiveContext is realized in Pinocchio, an experimental Smalltalk implementation that fully reifies the VM to enable radical extensions. We illustrate dynamic updates in ActiveContext with a typical use case, present initial benchmarks, and discuss future performance improvements.

Highly available software systems occasionally need to be updated while avoiding downtime. Dynamic software updates reduce downtime, but still require the system to reach a quiescent state in which a global update can be performed. This can be difficult for multi-threaded systems. We present a novel approach to dynamic updates using first-class contexts, called Theseus. First-class contexts make global updates unnecessary: existing threads run to termination in an old context, while new threads start in a new, updated context; consistency between contexts is ensured with the help of bidirectional transformations. We show that for multi-threaded systems with coherent memory, first-class contexts offer a practical and flexible approach to dynamic updates, with acceptable overhead.

Highly available software systems occasionally need to be updated while avoiding downtime. Dynamic software updates reduce downtime, but still require the system to reach a quiescent state in which a global update can be performed. This can be difficult for multi-threaded systems. We present a novel approach to dynamic updates using first-class contexts, called Theseus. First-class contexts make global updates unnecessary: existing threads run to termination in an old context, while new threads start in a new, updated context; consistency between contexts is ensured with the help of bidirectional transformations. We show that for multi-threaded systems with coherent memory, first-class contexts offer a practical and flexible approach to dynamic updates, with acceptable overhead.

Abstract. Scoping behavioral variations to dynamic extents is useful to support non-functional concerns that otherwise result in cross-cutting code. Unfortunately, such forms of scoping are difficult to obtain with traditional reflection or aspects. We propose delegation proxies, a dynamic proxy model that supports behavioral intercession through the interception of various interpretation operations. Delegation proxies permit different behavioral variations to be easily composed together. We show how delegation proxies enable behavioral variations that can propagate to dynamic extents. We demonstrate our approach with examples of behavioral variations scoped to dynamic extents that help simplify code related to safety, reliability, and monitoring.

Code duplication is common in current programming-practice: programmers search for snippets of code, incorporate them into their projects and then modify them to their needs. In today's practice, no automated scheme is in place to inform both parties of any distant changes of the code. As code snippets continues to evolve both on the side of the user and on the side of the author, both may wish to benefit from remote bug fixes or refinements-authors may be interested in the actual usage of their code snippets, and researchers could gather information on clone usage. We propose maintaining a link between software clones across repositories and outline how the links can be created and maintained.