This paper studies a behavioural theory of the p-calculus with session
types under the fundamental principles of the practice of distributed computing
— asynchronous communication which is order-preserving inside each connection
(session), augmented with asynchronous inspection of events (message arrivals).
A new theory of bisimulations is introduced, distinct from either standard
asynchronous or synchronous bisimilarity, accurately capturing the semantic nature
of session-based asynchronously communicating processes augmented with event
primitives. The bisimilarity coincides with the reduction-closed barbed congruence.
We examine its properties and compare them with existing semantics. Using the behavioural
theory, we verify that the program transformation of multithreaded into
event-driven session based processes, using Lauer-Needham duality, is type and semantic
preserving. Our benchmark results demonstrate the potential of the sessiontype
based translation as semantically transparent optimisation techniques.