Polyester is a tuple-space framework implemented in java, based on the lighTS framework by Gian Pietro Picco et al.
A first repository for polyester was created on sourceforge, but we are in the process of moving our repositories to GitHub, in order to benefit from the social network of github, and see the evolution of our projects.
Feel free to download or fork polyester, and any of our other projects!
Unlike most tuple-space implementations, polyester is meant to be integrated into a single application, rather than deployed in a client-server architecture.
Polyester was developed as a component of the U-P2P (for “Universal P2P”) file-sharing client, a research project at Carleton University. However, its implementation is completely independent of the file-sharing application, and polyester can be used to build any application where multiple processes are coordinated following the principles of so-called blackboard systems. Read on for more details.
The reader can get familiar with Polyester by running the application polyester.java in the package “example”.
Basic Principles
Tuple Spaces are systems that support coordination of various agents following a principle similar to the “blackboard architecture” defined in AI. The original idea of tuple spaces and the coordination model used in most implementations (including this one) was described by Gelertner are Carriero in a paper entitled “Coordination languages and their significance”, in 1992.
The basic principle of a tuple-space is that it allows agents to communicate asynchronously by posting and reading tuples to/from the shared “tuple space”. The different agents don’t necessarily need to know about each other’s existence, and problems may be solved by complex processes that unfold in an unplanned manner.
Agents can output tuples to the tuple space at any time, and read tuples by submitting a “template” to the tuple space: the operation retrieves all the tuples that match the template, according to matching rules outlined below. The tuples may be removed from the tuplespace, or the agent may only retrieve a copy (these are two different operations). In addition, the read operations may block until a matching tuple appears, or may simply retrieve any immediately present matching tuple, or /null/ if none are present.
The above operations are generic tuple-space operations defined in the Linda language. In Polyester, our implementation makes it particularly easy to implement agents based on a simple design, that of our AbstractWorker class. The worker has a number of templates, and continuously watches the tuples space. Any matching tuples are read (a copy retrieved), and processed in a FIFO order, possibly dumping new tuples as a response. The worker manages a queue and never processes the same tuple twice. An additional worker is provided (the CleaningWorker), which removes the tuples from the tuples-space after a determined lifetime.
The Cleaning worker and several workers based on the Abstract worker described above make up the central coordination component in our application U-P2P.
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