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Question about handling SIGINT properly in Guile

From: Vijay Marupudi
Subject: Question about handling SIGINT properly in Guile
Date: Sat, 13 Apr 2024 10:46:16 -0400

Hello folk of guile-user,

I am trying to create a simple Guile program that continues to perform a
task until an interrupt signal is sent. However, I am unable to
deterministically end the program when SIGINT is sent, as the
interrupt handler does not run soon after the call to (sleep ...) ends.

Try running the simple reproduction included below. Try typing ^C
(Ctrl+C) soon after the program begins. Sometimes "WORK" is run
once, and sometimes "WORK" is run twice. What do I need to do to make
"WORK" run only once in this instance?

(define quit? #f)

(sigaction SIGINT (lambda (arg)
                    (pk "SIG" arg)
                    (set! quit? #t)))

(let loop ()
  (pk "QUIT-CHECK")
  (if quit?
      (begin (format #t "Quitting!~%") (exit 0))
      (begin (pk "WORK" (do ((i 0 (+ i 1))
                             (sum 0 (+ sum i)))
                            ((= i 1000) sum)))
             (pk "SLEEP" (sleep 10))

I understand that signal handlers are asynchronous (Asyncs) and aren't
guaranteed to run immediately. However, I expect them to be run before
the next primitive call. Am I doing something wrong?

~ Vijay

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