[gambit-list] A rudimentary pipeline implementation with bridging threads
jpiitula at ling.helsinki.fi
Mon Jan 28 05:02:45 EST 2013
Assuming my previous question came through, I asked about implementing
pipelines of processes in Gambit-C. The problem was that I could not
seem to make the output of one process to connect to the input of the
next on their own.
I'm now experimenting with Gambit-C threads to bridge those gaps.
Here is a rudimentary implementation of what I want. The comments
indicate things that I think I know I still need to do. I haven't used
threads much before, and never in Scheme.
The original question stands: am I overlooking some obvious way to do
such pipelines that Gambit-C already has? Because this is the easy 80%
of the work and another 80% sheer tedium probably remains :)
(define (echo from to) ;should use a buffer
(do ((line (read-line from) (read-line from)))
(display line to)
(define (piece from to)
(echo from to) ;should allocate a private buffer for echo
(close-output-port to) ;stopped using it as output port
(process-status from))) ;wait for it - maybe time it out?
(define (end from) ;not closing current output port
(echo from (current-output-port))
;actually, the end should be controlled by the called altogether! or
;is it now?
;caller needs to close the first pipe segment as output port, and do I
;need to force some output or close input ports? and errors should be
;handled, including diagnostic output from the processes and failed
;status of any, and not leave processes around on any sort of error if
;possible. oh and do all those threads terminate nicely and always?
(define (pipe first . rest)
(let ((first (open-process first)))
(do ((last first (car rest))
(rest (map open-process rest) (cdr rest)))
(thread-start! (make-thread (end last)))
;;^altogether mistaken - leave it to the caller
(values first last))
(thread-start! (make-thread (piece last (car rest)))))))
(define (test) ;has hardwired end to echo the output in current output
(call-with-values ;^fix it so the called handles reading and waiting
(pipe "date" '(path: "tr" arguments: ("0-9" "D"))))
(lambda (first last)
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