Incremental Dynamic Updates with First-Class Contexts

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 firstclass 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 how first-class contexts offer a practical and flexible approach to incremental dynamic updates, with acceptable overhead.