Toward Sequentializing Overparallelized Protocol Code

In our ongoing work, we use constraint automata to compile protocol specifications expressed as Reo connectors into efficient executable code, e.g., in C. We have by now studied this automata based compilation approach rather well, and have devised effective solutions to some of its problems. Because our approach is based on constraint automata, the approach, its problems, and our solutions are in fact useful and relevant well beyond the specific case of compiling Reo. In this short paper, we identify and analyze two such rather unexpected problems.Comment: In Proceedings ICE 2014, arXiv:1410.701

Can High Throughput Atone for High Latency in Compiler-Generated Protocol Code? (Technical Report)

High-level concurrency constructs and abstractions have several well-known software engineering advantages when it comes to programming concurrency protocols among threads in multicore applications. To also explore their complementary performance advantages, in ongoing work, we are developing compilation technology for a high-level coordination language, Reo, based on this language's formal automaton semantics. By now, as shown in our previous work, our tools are capable of generating code that can compete with carefully hand-crafted code, at least for some protocols. An important prerequisite to further advance this promising technology, now, is to gain a better understanding of how the significantly different compilation approaches that we developed so far, which vary in the amount of parallelism in their generated code, compare against each other. For instance, to better and more reliably tune our compilers, we must learn under which circumstances parallel protocol code, with high throughput but also high latency, outperforms sequential protocol code, with low latency but also low throughput. In this paper, we report on an extensive performance comparison between these approaches for a substantial number of protocols, expressed in Reo. Because we have always formulated our compilation technology in terms of a general kind of communicating automaton (i.e., constraint automata), our findings apply not only to Reo but, in principle, to any language whose semantics can be defined in terms of such automata

Composing Constraint Automata, State-by-State (Technical Report)

The grand composition of n automata may have a number of states/transitions exponential in n. When it does, it seems not unreasonable for the computation of that grand composition to require exponentially many resources (time, space, or both). Conversely, if the grand composition of n automata has a number of states/transitions only linear in n, we may reasonably expect the computation of that grand composition to also require only linearly many resources. Recently and problematically, we saw cases of linearly-sized grand compositions whose computation required exponentially many resources. We encountered these cases in the context of Reo (a graphical language for coordinating components in component-based software), constraint automata (a general formalism for modeling systems' behavior), and our compiler for Reo based on constraint automata. Combined with earlier research on constraint automata verification, these ingredients facilitate a correctness-by-construction approach to component-based software engineering---one of the hallmarks in Sifakis' "rigorous system design". To achieve that ambitious goal, however, we need to solve the previously stated problem. In this paper we present such a solution