Concurrency in Microprotocol Frameworks

Protocol stacks and other distributed applications have been structured as a set of collaborating components with more or less well-defined interfaces. Recent frameworks provide flexible interfaces, arrangements and communication patterns, and thus allow for finer-grained components, called microprotocols. Multi-threaded programming is the key to high performance in these frameworks. This paper investigates what support for multi-threaded programming such frameworks provide and should provide for programmers. Along with a survey and detailed discussions of the features of existing frameworks, we propose features that can be offered without significant changes in programs, and that have a negligible performance impact. This includes the following: (1) sets of single-threaded microprotocols that coexist with multi-threaded microprotocols, thus taking the best of two worlds; (2) non-overlapping execution of microprotocols involved in a chain of asynchronous communication, to avoid inconsistencies; and (3) ordering guarantees for asynchronous communication among microprotocols. To our knowledge, our definition for a particular extension of causal order is the simplest so far.