Lambda the Ultimate

The Joins Concurrency Library. Claudio Russo.

Comega extended C# 1.x with a simple, declarative and powerful model of concurrency - join patterns - applicable both to multithreaded applications and to the orchestration of asynchronous, event-based distributed applications. With Generics available in C# 2.0, we can now provide join patterns as a library rather than a language feature. The Joins library extends its clients with an embedded, type-safe and mostly declarative language for expressing synchronization patterns. The library has some advantages over Comega: it is language neutral, supporting other languages like Visual Basic; its join patterns are more dynamic, allowing solutions difficult to express with Comega; its code is easy to modify, fostering experimentation.

In the Joins library, the scheduling logic that would be compiled into the corresponding Comega class receives a separate, first-class representation as an object of the special Join class. The Join class provides a mostly declarative, type-safe mechanism for defining thread-safe synchronous and synchronous communication channels and patterns. Instead of (a)synchronous methods, as in Comega, the communication channels are special delegate values (first-class methods) obtained from a common Join object. Communication and/or synchronization takes place by invoking these delegates, passing arguments and optionally waiting
for return values.

The library also supports dynamic joins, which are not available in Comega, implemented by joining arrays of channels (with the size of the array being determined at runtime).

The major weakness of the Joins library is speed, since the static apporach of Comega provides more room for optimization (see the brief discussion in sec. 6).