[racket-dev] Testing whether a procedure gets collected

On Sun, Dec 2, 2012 at 11:40 PM, Neil Toronto <neil.toronto at gmail.com> wrote:
> On 12/02/2012 12:10 PM, Robby Findler wrote:
>>
>> On Sun, Dec 2, 2012 at 11:43 AM, Matthias Felleisen
>> <matthias at ccs.neu.edu> wrote:
>>>
>>>
>>> On Dec 1, 2012, at 9:23 PM, Robby Findler wrote:
>>>
>>>> I think the high-level answer is that you have to understand something
>>>> about details that aren't currently specified but nevertheless are how
>>>> things currently work and then make a test that will work when you
>>>> make those additional assumptions (and then keep it running in drdr so
>>>> you can tell when the assumptions get broken).
>>>
>>>
>>>
>>> Doesn't this suggest deep down that Neil is trying to 'beat'
>>> Racket and its implementation with his program? I think the
>>> entire discussion (I didn't follow every detail) points to
>>> something lacking about the language. -- Matthias
>>
>>
>> I think that Neil wants to formulate a test case that checks that his
>> datastructure doesn't leak and is complaining about the lack of
>> specification for what "If the garbage collector has proven" (quote
>> from the docs) means.
>
>
> I didn't mean to sound complain-y... :p

Oh no. "complain" here was not meant to be a negative. Sorry. You
"expressed dissatisfaction" and I think it is reasonable to do so.

>> My experience with similar testing is that the level of specification
>> is actually okay. I can't speak for finalizers (they are more complex)
>> but weak boxes seem fine.
>
>
> And that helps a lot, so thanks!
>
> You're both right, of course. I'm essentially trying to test something that
> is unobservable. The fact that I can observe it is an implementation
> accident. The specific accident, that a weak box is cleared as soon as
> possible, happens to be common and generally expected.
>
> I don't know whether it's worth it in this case to tighten the
> specification. I don't want anyone to spend time on it unless it's actually
> worth researching.

I don't know that there is a paper to be found, but I agree that an
informal description that explains a little more about when one can
intuitively expect a weak box to be cleared seems useful.

I agree that when something is collected is a pretty intentional
property but I think it is possible to say a little bit more since
there is a pretty stable core idea there (namely that if something
isn't reachable and you call collect-garbage you can be pretty sure
it'll be gone -- this was not the case back in the boehm gc days).

Hm. I'll think more about this and see if I can improve the docs.

Robby