When you use `system` or `process`, the immediate new process runs a
shell. The shell process then starts another one to run the command
that you give it.
I recommend using `process*` to avoid the shell process and to avoid
encoding issues when passing arguments:
(define racket (find-executable-path "racket"))
... (process* racket "sleeper.rkt") ...
Another approach is to create a fresh process group for the shell
process, and then `((fifth pl) 'kill)` kills the whole group:
(parameterize ([subprocess-group-enabled #t])
(process "racket sleeper.rkt"))
Finally, you could tell the shell to not create a subprocess and
instead replace itself with the other program"
(process "exec racket sleeper.rkt")
At Thu, 7 Apr 2016 13:47:39 -0700 (PDT), Wayne Iba wrote:
> I'm having trouble with two interacting processes and am hoping someone can
> point out whatever it is that I'm missing.
>
> Process A starts process B and interacts with it but conditionally needs to
> kill it. But using the procedure of one argument returned (as the fifth
> element of a list) by process does not seem to kill it. I've tried "kill -9
> <pid>" with system with no joy either. Here is my code and the output from
> killer.
> =======================
> ;code for sleeper in a separate file
> (define (sleeper)
> (for ([i 7])
> (sleep 4)
> (printf "~a~%" i)(flush-output)))
> (sleeper)
> =======================
> ;code for killer in another file -- I run this as "racket killer.rkt"
> (define (killer)
> (let ([pl (process "racket sleeper.rkt")])
> (for ([l (in-port read-line (first pl))])
> (printf "status: ~a~%" ((fifth pl) 'status))
> (if (= (with-input-from-string l read) 2)
> (begin
> ;(system (string-append "kill -9 " (number->string (third pl))))
> ((fifth pl) 'kill)
> )
> (displayln l)))
> (close-input-port (first pl))
> (close-output-port (second pl))
> (close-input-port (fourth pl))
> ))
> (killer)
> =======================
> ;; output from killer
> status: running
> status: running
> 0
> status: running
> 1
> status: running
> status: done-error
> 3
> status: done-error
> 4
> status: done-error
> 5
> status: done-error
> 6
> =======================
>
> So what am I missing? Thanks in advance!
>
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