Deterministic Concurrency Using Lattices and the Object Capability Model

University essay from KTH/Skolan för elektroteknik och datavetenskap (EECS)

Abstract: Parallelization is an important part of modern data systems. However, the non-determinism of thread scheduling introduces the difficult problem of considering all different execution orders when constructing an algorithm. Therefore deterministic-by-design concurrent systems are attractive. A new approach called LVars consists of using data which is part of a lattice, with a predefined join operation. Updates to shared data are carried out using the join operation and thus the updates commute. Together with limiting the reads of shared data, this guarantees a deterministic result. The Reactive Async framework follows a similar approach but has several aspects which can cause a non-deterministic result. The goal with this thesis is to explore how we can ammend Reactive Async in order to guarantee a deterministic result. First an exploration into the subtleties of lattice based data combined with concurrency is made. Then a formal model based on a simple object-oriented language is constructed. The constructed small-step operational semantics and type system are shown to guarantee a form of determinism. This shows that LVars-similar system can be implemented in an object-oriented setting. Furthermore the work can act as a basis for future revisions of Reactive Async and similar frameworks.

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