Welcome to the CHICKEN Scheme pasting service

(import (srfi 18))

(define m (make-mutex))
(define c (make-condition-variable))

(define countdown 5)

(define j
  (thread-start!
   (lambda ()
     (let loop ()
       (mutex-lock! m)
       (if (zero? countdown)
           (print "blastoff!")
           (begin
             (mutex-unlock! m c)
             (loop)))))))

(do ()
    ((zero? countdown))
  (print "blastoff in " countdown "...")
  (thread-sleep! 1)
  (set! countdown (sub1 countdown))
  (condition-variable-signal! c))

(thread-join! j)

(import (chicken process signal))
(import srfi-18)

(define (make-handler cv msg)
  (lambda (signum)
    (print msg " signal")
    (condition-variable-specific-set! cv 'break)
    (condition-variable-signal! cv)))

(let [(m (make-mutex))
      (cv (make-condition-variable))]
  (condition-variable-specific-set! cv 'hold)
  (set-signal-handler! signal/int (make-handler cv "INT"))
  (thread-start! (lambda ()
                   (sleep 4)
                   (condition-variable-specific-set! cv 'break)
                   (condition-variable-signal! cv)))
  (let loop ()
    (print "+ loop")
    (mutex-lock! m)
    (print "+ unlock")
    (mutex-unlock! m cv)
    (when (equal? 'hold (condition-variable-specific cv))
      (loop))
    (print "done")))