At Thu, 6 Sep 2012 16:43:09 -0700, Kartik Agaram wrote: > I'm trying to build an output port that acts like 'tee', wrapping two > (or more) output ports and duplicating writes to them. This requires > make-output-port > (http://docs.racket-lang.org/reference/customport.html#%28def._%28%28quote._~23 > ~25kernel%29._make-output-port%29%29), > right? I'm trying to think about what the evt arg to make-output-port > should be. It needs to be the AND of the sync-readiness of all the > constituent ports, right? Is there a way to specify that? choice-evt > (http://docs.racket-lang.org/reference/sync.html#%28def._%28%28quote._~23~25ker > nel%29._choice-evt%29%29) > is an OR, if I'm reading the docs right..
No, there's no way to "and" events. (Racket's scheduler provides 1-way rendezvous, and it turns out that you can't get to N-way rendezvous from 1-way rendezvous.) The only way out is to always internally buffer at least one byte. From the outside, the byte counts as committed to the port at the point that it's internally buffered; don't accept more bytes until the buffer can be cleared. Your output port will likely provide the guarantee that all bytes are delivered to the destination ports only when it is finally closed. ____________________ Racket Users list: http://lists.racket-lang.org/users
