Analyzing permission transfer channels for dynamically typed languages

Abstract

Communicating Sequential Process (CSP) is nowadays a popular concurrency model in which threads/processes communicate by exchanging data through channels. Channels help in orchestrating concurrent processes but do not solve per-se data races. To prevent data races in the channel model, many programming languages rely on type systems to express ownership and behavioural restrictions such as immutability. However, dynamically-typed languages require run-time mechanisms because of the lack of type information at compile-time.

In this paper, we propose to augment channels with four different permission transfer semantics. We explore two mechanisms to implement such permission transfers at run time: write barriers and partial-read barriers. To validate our approach we implemented a channel framework in Pharo, and we extended it with different permission transfer semantics. We report on performance measurements of both (a) the transfer overhead on a single object and on a graph of objects, and (b) the per-object access overhead incurred by ownership checks. This work stands as a cornerstone of future work on adaptive optimizations for permission transfer channels.