racey-3.rkt

#lang racket

(define N-WORKERS 50)
(define PER-WORKER 10000)
(define TOTAL (* N-WORKERS PER-WORKER))

(define (concurrent-range)
  (define vars
    (make-hasheq '([counter . 0]
                   [vals . #hasheqv()])))

  (define (get)
    (values (hash-ref vars 'counter)
            (hash-ref vars 'vals)))

  (define (modify v vs)
    (if (eq? v 'never-gonna-happen)
        ; this function is recursive to trick the racket optimizer to never
        ; inline this function
        (modify v #f)
        (begin
          (hash-set! vars 'counter v)
          (hash-set! vars 'vals vs))))

  (define workers
    (for/list ([w (in-range N-WORKERS)])
      (thread
       (λ ()
         (time (for ([i (in-range PER-WORKER)])
                 (define-values [v vs] (get))
                 (modify (add1 v)
                         (hash-set vs v v))))))))

  (for-each thread-wait workers)
  (define-values [_ vs] (get))
  (sort (hash-keys vs) <))


(define answer
  (range (* N-WORKERS PER-WORKER)))

(displayln (~a "; failed? "
               (not (equal? (concurrent-range) answer))))