Paper Details

%T An occam Model of XCHANs
%A Peter H. Welch
%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 Øyvind Teig, in \[dq]XCHANs: Notes on a New Channel
   Type\[dq], proposed a higher level channel construct (XCHAN)
   that attempts to reconcile those wedded to asynchronous
   message passing with the synchronous form in CSP. Sending a
   message does not block the sender, but the message may not
   get sent: the sender receives a success/fail result on
   each send. The XCHAN provides a conventional feedback
   channel on which it signals when it is ready to take a
   message. Being ready means that it has space (if it is
   buffered) or a reading process has committed to take the
   message (if it is not buffered). Sending to a ready
   XCHAN always succeeds; sending to an XCHAN that is not ready
   always fails. The sender can always wait for the signal from
   the XCHAN (whilst ALTing on, and processing, other events)
   before sending. We can model an XCHAN by a process in
   occam\-pi. Buffered XCHANs are easy. Zero\-buffered XCHANs
   are a little harder, because we need to
   maintain end\-to\-end synchronisation. However,
   occam\-pi\[rs]s extended input (??) and output (!!)
   primitives enable the process implementing the XCHAN to be
   hidden from its users. Unfortunately, extended outputs are
   not yet in the language, but their semantics can be
   simulated by making the receiving process read twice and
   ignore the first (which is just a signal whose taking must
   commit the reader to its second read). An important message
   is that sane higher level synchronisation mechanisms are
   usually not hard to implement efficiently via the low level
   CSP primitives offered by occam\-pi. Although not yet
   measured for XCHANs, it is likely that such simulation in
   occam\-pi will have competitive performance with direct
   implementation elsewhere.

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