Selective Choice 'Feathering' with XCHANs

摘要

This paper suggests an additional semantics to XCHANs, where a sender to a synchronous channel that ends up as a component in a receiver's selective choice (like ALT) may (if wanted) become signaled whenever the ALT has been (or is being) set up with the actual channel not in the active channel set. Information about this is either received as the standard return on XCHANs attempted sending or on the built-in feedback channel (called x-channel) if initial sending failed. This semantics may be used to avoid having to send (and receive) messages that have been seen as uninteresting. We call this scheme feathering, a kind of low level implicit subscriber mechanism. The mechanism may be useful for systems where channels that were not listened to while listening on some other set of channels, will not cause a later including of those channels to carry already declared uninteresting messages. It is like not having to treat earlier bus-stop arrival messages for the wrong direction after you sit on the first arrived bus for the correct direction. The paper discusses the idea as far as possible, since modeling or implementation has not been possible. This paper's main purpose is to present the idea.