[racket] Destructors in Racket

 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
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