A Haskell-Implementation of STM Haskell with Early Conflict Detection

Abstract: Software transactional memory treats operations on the shared memory in concurrent programs like data base transactions. STM Haskell integrates this approach in Haskell and provides combinators to build software transactions in a composable way. In previous work we introduced the process calculus CSHF as a formal model for a concurrent implementation of software transactional memory in Concurrent Haskell. The correctness of CSHF with respect to a specification semantics was shown by using techniques from programming languages semantics. In this paper we first describe the CSHF semantics informally to illustrate the ideas of our approach. Secondly, we report on the implementation of the CSHF semantics as a library for software transactional memory in Haskell. In difference to the implementation available in the Glasgow Haskell Compiler our approach performs conflict detection as early as a possible, does not use pointer equality to test for conflicts and it is written in Haskell and thus not part of the runtime system. Besides explaining the features of CSHF and comparing them to the approach taken in the Glasgow Haskell Compiler, we explain in detail our design choices of the implementation.