[racket-dev] Testing whether a procedure gets collected

Honestly, because I was too rushed to try them before I had to leave 
this morning. :D However, now that I have the chance, I've found that 
Typed Racket doesn't support them. I can't add support using 
`required/typed', because `Weak-Box' would have to be a polymorphic type.

Also, they don't seem to let go of procedure values. This one's value 
doesn't ever turn to #f no matter how many times I collect garbage:

   (define bx (make-weak-box (λ (_) 0)))

Thinking it might be because that lambda doesn't create a closure, I 
tried this:

   (define (make-box-thing v)
     (make-weak-box (λ (_) v)))

   (define bx (make-box-thing 4))

But this `bx' doesn't let go of its value, either. I can't help but 
think I'm missing something really stupid, though.

Neil ⊥

On 12/01/2012 10:58 AM, Robby Findler wrote:
> How about using a weak box instead?
>
> Robby
>
> On Sat, Dec 1, 2012 at 11:45 AM, Neil Toronto <neil.toronto at gmail.com> wrote:
>> I'm getting ready to push a change to math/array that fixes a memory leak.
>> I've devised a test that I think will determine whether an array's procedure
>> gets collected after the array is made strict, but I don't know whether it
>> works only by accident. Here it is:
>>
>>
>> (define: collected? : (Boxof Boolean)  (box #f))
>>
>> (define arr
>>    (let ([proc  (λ: ([js : Indexes]) 0)])  ; constant array
>>      (register-finalizer proc (λ (proc) (set-box! collected? #t)))
>>      (build-array #() proc)))
>>
>> (array-strict! arr)
>> (collect-garbage)
>> (sleep 0)  ; give finalizers a chance to run?
>> (check-true (unbox collected?))
>>
>>
>> This test passes for me now, but will fail if anyone else tries it. What
>> worries me is that (sleep 0) is apparently required, meaning that finalizers
>> aren't run immediately when garbage is collected.
>>
>> How can I ensure that the finalizer for `proc' gets run before I test the
>> value of `collected?'?
>>
>> Neil ⊥
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