A 2nd Generation Network Distributed Application Programming Interface for Epics

The programming interface for developing EPICS 1 network distributed applications is called Channel Access. A high priority has been placed on stability and backwards compatibility with this interface, and accordingly it has undergone relatively few externally visible revisions during the lifespan of EPICS. There are of course fundamental tensions where the desire to maintain a stable interface competes with freedom to make technological improvements, and we expect to accomplish more when we have opportunities to make structural changes that will be seen by users. We have an accumulated list of potential improvements all motivated by weaknesses we can identify in the current interface. For example, the set of available meta-data, the mix of meta-data, and the extent that multiple parameters might be synchronized together into a command-response message must be application extensible. Likewise, the EPICS system, which is based on the publish-and-subscribe distributed system model, needs an application extensible set of subscription update triggering events along with additional flexibility related to client application specification of server event filtering, event matching, and property matching combinatorial expressions. Having recently completed a major release, the EPICS core developers are emerging from a code-polishing phase, and are in the midst of addressing the restrictions mentioned above. Our functional requirements and fundamental design decisions are discussed. Finally, some example code is provided in order to give some perspective for code authors who might use this interface.