Friday, December 28, 2007


naasking mentioned that Manticore has nested schedulers - sounds very interesting, and similar to what I want to achieve in Fluid. Must read that.

Thursday, December 27, 2007

Fluid preManifesto

At this point of my life I don't have much time to actively pursue the research I would like to. I decided to make an overview of what is envisioned, so that at least I do not forget that myself when I have spare minute or two.

Fluid is a codename for programming language/framework/calculus/tool that should enable experiments with and teaching of various approaches to concurrency and possibly parallelism.
During my initial experiments with join calculus I decided that a lot of interesting stuff is being swept under the carpet. For one thing, scheduling of reactions is implicit on one hand, and rigid on the other. What if one had a language in which diving into the gory details of scheduling would be a matter of using some operator, like call/cc is being used to dive into underlying continuations? No scheduling would be left implicit, all interleaving would be deterministic and controlled - mostly using popular constructs from the library in a very lean syntactic way (monadic reflection?), but occasionally giving possibility to do exactly what is needed. At runtime, something similar to engines looks promising.

The language would follow the maxim Algorithm = Logic + Control, separating declarative part of the solution from the control of when to pursue which way and for how long. It must be possible to ration CPU cycles and other resources based on the perceived relative utility of the computations, as well as to prune the computations that are believed to have too few value to be worth any future resources. This utility-aware side of the research might come close to the mechanism design (most probably the algorithmic branch of it).

Having outsourced the scheduling to the user code, the next question is how to express the declarative part of the solution. After playing with various alternatives (promises, MVars, channels) I decided that concurrent constraint programming looks most general of them all. But which constraint system to choose? Or should I choose some specific system at all? As control part is very customizable, why not follow the same path in the logical part? I don't yet know the details, or whether it is possible at all, but the idea is to allow user code to define the constraint system as well.

To put it all in one line: Program = Logic + Control, Your Way, Best Value for Resources!

I would like to write much more, but my margin (of time) is too small, so I finish here.

Tuesday, December 11, 2007

A Software Architecture for Distributed Control Systems and Its Transition System Semantics

A software architecture for distributed control systems is presented that is based on a shared data space coordination model. The architecture, named SPLICE, is introduced in two steps.First we give the general structure of the coordination model including the shared data space and the basic operations and we define its semantics by means of a transition system. Second we present a transition system for a refinement of the coordination model: data is distributed and replicated across a communication network using a publication-subscription protocol. We also discuss methods in SPLICE for fault-tolerance and the possibility for on-line system modification and extensions.

Similar to Linda, JavaSpaces, and other paradigms of communication via shared store.