Synchronization Views for Event-loop Actors

摘要

The actor model has already proven itself as an interesting concur-rency model that avoids issues such as deadlocks and race condi-tions by construction, and thus facilitates concurrent programming. The tradeoff is that it sacrifices expressiveness and efficiency es-pecially with respect to data parallelism. However, many standard solutions to computationally expensive problems employ data par-allel algorithms for better performance on parallel systems. We identified three problems that inhibit the use of data-parallel algorithms within the actor model. Firstly, one of the main prop-erties of the actor model, the fact that no data is shared, is one of the most severe performance bottlenecks. Especially the fact that shared state can not be read truly in parallel. Secondly, the actor model on its own does not provide a mechanism to specify extra synchronization conditions on batches of messages which leads to event-level data-races. And lastly, programmers are forced to write code in a continuation-passing style (CPS) to handle typical request-response situations. However, CPS breaks the sequential flow of the code and is often hard to understand, which increases complexity and lowers maintainability. We proposes synchronization views to solve these three is-sues without compromising the semantic properties of the actor model. Thus, the resulting concurrency model maintains deadlock-freedom, avoids low-level race conditions, and keeps the semantics of macro-step execution.