Re: [Sbcl-devel] Two apparent bugs in multi-threading

[Nikodemus S. <nik...@ra...>]

On Sun, 21 Aug 2005, Christopher Neufeld wrote:

> (defun main ()
>  (dotimes (i 100)
>    (sb-thread:make-thread #'(lambda () (worker i)))))

> The output of (main) should be the integers from 0 to 99, not necessarily
> in order.  Instead, a typical run will produce the number 13 seven times,
> then the number 20 seven times, then the number 27 seven times, then the
> number 33 twelve times, and so on.  Finally, it will print the number 100 a
> few times.  This appears to be because by the time the closure is evaluated
> to create the new thread, the value of 'i' has been incremented, maybe
> several times.

Right on mark up till this point. However, the solution is much simpler:

(defun main ()
   (dotimes (i 100)
     (let ((ti i))
       (sb-thread:make-thread #'(lambda () (worker ti))))))

...introduce a separate binding for each thread. (Untested, not having
an x86 Linux handy.)

Cheers,

  -- Nikodemus              Schemer: "Buddha is small, clean, and serious."
                   Lispnik: "Buddha is big, has hairy armpits, and laughs."