Globally Governed Session Semantics

This paper proposes a bisimulation theory based on multiparty session types where achoreography specification governs the behaviour of session typed processes and their observer. Thebisimulation is defined with the observer cooperating with the observed process in order to formcomplete global session scenarios and usable for proving correctness of optimisations for globallycoordinating threads and processes. The induced bisimulation is strictly more fine-grained than thestandard session bisimulation. The difference between the governed and standard bisimulations onlyappears when more than two interleaved multiparty sessions exist. This distinct feature enables toreason real scenarios in the large-scale distributed system where multiple choreographic sessionsneed to be interleaved. The compositionality of the governed bisimilarity is proved through thesoundness and completeness with respect to the governed reduction-based congruence. Finally, itsusage is demonstrated by a thread transformation governed under multiple sessions in a real usecasein the large-scale cyberinfrustracture.