Software Transactions

Join-calculus

A general trend in programming languages is to evolve towards higher levels of abstractions. For example the goto statement has been replaced by structured loop constructs. One of the main benefits of doing so is a massive improvement in readability. The standard concurrency constructs have not followed the same evolution; most of them are still low-level and haven’t changed much in the last thirty or forty years. Semaphores (1968) and monitors (1974) still form the concurrency basis for many “modern” languages such as Java and C#. These low-level constructs neither compose well, nor do they promote a modular approach; too often they result in programs which are difficult to understand and debug. So just like modular and structured programming facilitates abstraction and composition, we need to find similar models for concurrent programming.

Join-calculus is an elegant and simple yet powerful synchronization model. It is based on the pattern matching of messages and the execution of a block of code on matches. It was developed at INRIA in the 90’s and first implemented in JoCaml. Several implementations exist, either as libraries (e.g. Boost Join, Joins Concurrency Library) or as a language feature (Funnel, Join-Java, Cw/Polyphonic C#, MC#, VB, VODKA).
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