Reo Coordination Language
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Reo is a domain-specific language for programming and analyzing coordination protocols that compose individual processes into full systems, broadly construed. Examples of classes of systems that can be composed with Reo include component-based systems, service-oriented systems, multithreading systems, biological systems, and cryptographic protocols. Reo has a graphical syntax in which every Reo program, called a connector or circuit, is a labeled directed hypergraph. Such a graph represents the data-flow among the processes in the system. Reo has formal semantics, which stand at the basis of its various formal verification techniques and compilation tools.
In Reo, a concurrent system consists of a set of components which are glued together by a circuit that enables flow of data between components. Components can perform I/O operations on the boundary nodes of the circuit to which they are connected. There are two kinds of I/O operations: put-requests dispatch data items to a node, and get-requests fetch data items from a node. All I/O operations are blocking, which means that a component can proceed only after its pending I/O operation has been successfully processed.
The figure on the top-right shows an example of a producers-consumer system with three components: two producers on the left and one consumer on the right. The circuit in the middle defines the protocol, which states that the producers should send data synchronously, while the consumer receives those data in alternating order.
Formally, the structure of a circuit is defined as follows:
Definition 1. A circuit is a triple where:
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