%T Selective Choice \[dq]Feathering\[dq] with XCHANs
%A  Øyvind Teig
%E Peter H. Welch,  Frederick R. M. Barnes,  Jan F. Broenink,  Kevin Chalmers,  Jan Bækgaard Pedersen,  Adam T. Sampson
%B Communicating Process Architectures 2013
%X This paper suggests an additional semantics to XCHANs, where
   a sender
to a synchronous channel that ends up as a
   component in a receiver\[rs]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 XCHAN\[rs]s 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\[rs]s main purpose is to present the idea.