Dynamic Dataflow Modeling in Ptolemy

Dataflow process networks are a special case of Kahn process networks (PN). In dataflow process networks, each process consists of repeated firings of a dataflow actor, which defines a quantum of computation. Using this quantum avoids the complexities and context switching overhead of process suspension and resumption incurred in most implementations of Kahn process networks. Instead of context switching, dataflow process networks are executed by scheduling the actor firings. This scheduling can be done at compile time for synchronous dataflow (SDF) which is a particularly restricted case with the extremely useful property that deadlock and boundedness are decidable. However, for the most general dataflow, the scheduling has to be done at run time and questions about deadlock and boundedness cannot be statically answered. This report describes and implements a dynamic dataflow (DDF) scheduling algorithm under Ptolemy II framework based on original work in Ptolemy Classic. The design of the algorithm is guided by several criteria that have implications in practical implementation. We compared the performance of SDF, DDF and PN. We also discussed composing DDF with other models of computation (MoC). Due to Turing-completeness of DDF, it is not easy to define a meaningful iteration for a DDF submodel when it is embedded inside another MoC. We provide a suite of mechanisms that will facilitate this process. We give several application examples to show how conditionals, data-dependent iterations, recursion and other dynamic constructs can be modeled in the DDF domain. 4 5 Acknowledgements I would like to thank my research advisor, Professor Edward A. Lee, not only for his encouragement and support during my most difficult time, but also for the pleasant group atmosphere and outstanding research environment he created. I am deeply inspired by his enthusiasm and devotion to pursuing excellent research. I would also like to thank Professor Alberto Sangiovanni-Vincentelli for kindly agreeing to serve as the second reader of this report and providing valuable comments. I would like to thank all of my colleagues in the Ptolemy group for creating such an excellent software environment and for all the stimulating discussions. Although I am an audience much of the time, I enjoyed every minute of it. Finally, I would like to thank my wife Yan and my parents for their continuous love and encouragement. This report is dedicated to them.