The Essence of Synchronisation in Asynchronous Data Flow

We discuss the aspect of synchronisation in the language design and implementation of the asynchronous data flow language S-Net. Synchronisation is a crucial aspect of any coordination approach. S-Net provides a particularly simple construct, the synchrocell. As a primitive S-Net language construct synchrocell implements a one-off synchronisation of two data items of different type on a stream of such data items. We believe this semantics captures the essence of synchronisation, and no simpler design is possible. While the exact built-in behaviour as such is typically not what is required by S-Net application programmers, we show that in conjunction with other language features S-Net synchrocells meet typical demands for synchronisation in streaming networks quite well. Moreover, we argue that their simplistic design, in fact, is a necessary prerequisite to implement an even more interesting scenario: modelling state in streaming networks of stateless components. We finish with the outline of an efficient implementation by the S-Net runtime system.