[racket] Destructors in Racket

 Here we have a thread per every module, that use such approach. It is better,than a thread per object, but ...
How many such threads can Racket run without performance degrading?

Maybe better make common module for such purpose? Hmm..., I think I should make one...


Sat, 2 Aug 2014 07:38:08 -0500 от Robby Findler <robby at eecs.northwestern.edu>:
>Probably you want to do something like this, I guess. It creates a
>single thread that just waits until anything registered with
>an-executor is garbage and then runs the executors. They will run
>asynchronously, but perhaps that's okay for your usecase.
>
>Robby
>
>#lang racket
>(define an-executor (make-will-executor))
>(void
> (thread
>  (λ ()
>    (let loop ()
>      (will-execute an-executor)
>      (loop)))))
>
>(define a-box (box #f))
>(will-register an-executor
>               a-box
>               (λ (x) (printf "a-box is now garbage\n")))
>(collect-garbage) (collect-garbage) (collect-garbage)
>(printf "breaking the link\n")
>(set! a-box #f)
>(collect-garbage) (collect-garbage) (collect-garbage)
>
>On Sat, Aug 2, 2014 at 7:31 AM, Roman Klochkov < kalimehtar at mail.ru > wrote:
>> So I can write
>>
>> (define (make-obj stream)
>>    (define res  (obj (open-output-file "out.dat")))
>>    (define will (make-will-executor))
>>    (will-register will res (lambda (x) (close-output-port (obj-file x))))
>>    (thread (lambda () (let loop () (will-try-execute will) (sleep 1)
>> (loop)))))
>>
>> to make my objects? Additional threads don't hinder performance, do they?
>>
>> Or should I somehow figure out if the thread is already running, don't run
>> it and use common `will' for all objects?
>>
>> Sat, 2 Aug 2014 07:00:04 -0500 от Robby Findler
>> < robby at eecs.northwestern.edu >:
>>
>> One way is to set up a separate thread to do that.
>>
>> The reason they are not called automatically is sometimes running the
>> procedure passed to will-register needs to access some shared state
>> and so your program must be allowed to be in control of the timing of
>> the executor.
>>
>> In this case, it sounds like you can run the executor at any time, so
>> just creating a thread to close the port inside my-obj should work
>> fine.
>>
>> Robby
>>
>>
>> On Sat, Aug 2, 2014 at 6:15 AM, Roman Klochkov < kalimehtar at mail.ru > wrote:
>>> Then how?
>>>
>>> Suppose I have
>>> (struct obj (file))
>>> (define my-obj (obj (open-output-file "out.dat")))
>>>
>>> What I have to write to close the file, when my-obj will be GC'ed?
>>>
>>> I can write
>>> (define will (make-will-executor))
>>> (will-register will my-obj (lambda (x) (close-output-port (obj-file x))))
>>>
>>> But as far as I understand, it will not be called until `will-execute' or
>>> `will-try-execute' will be manually called?
>>>
>>> Then how to call will-try-execute when GC is collecting my-obj?
>>>
>>>
>>> Sat, 2 Aug 2014 11:57:32 +0100 от Matthew Flatt < mflatt at cs.utah.edu >:
>>>
>>> No, use the safe "will executors" API, instead.
>>>
>>> The unsafe finalizer API is for low-level, atomic finalization. Closing a
>>> port can flush buffers and more, and it's not a good idea to do that in an
>>> unsafe atomic context.
>>>
>>>> On Aug 2, 2014, at 11:12 AM, Roman Klochkov < kalimehtar at mail.ru > wrote:
>>>>
>>>> I have a structure, that has a filestream inside it. File have to be
>>>> cosed, when the structure is not used anymore (so gargbage collected).
>>>>
>>>> Is the best way to do
>>>> (require ffi/unsafe)
>>>> (register-finalizer my-obj
>>>> (lambda (x) (close-output-port (obj-file x))))
>>>>
>>>> ?
>>>>
>>>> It seems doing right thing, but why `ffi/unsafe'? Is it OK, when my
>>>> program actually doesn't use FFI?
>>>>
>>>>
>>>> --
>>>> Roman Klochkov
>>>> ____________________
>>>> Racket Users list:
>>>>  http://lists.racket-lang.org/users
>>>
>>>
>>>
>>> --
>>> Roman Klochkov
>>>
>>> ____________________
>>> Racket Users list:
>>>  http://lists.racket-lang.org/users
>>>
>>
>>
>>
>> --
>> Roman Klochkov


-- 
Roman Klochkov
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