[racket] Destructors in Racket

 > But in case of another kind of value

What another kiind? Small numbers and some chars are not garbage collected.


Sat, 02 Aug 2014 22:47:32 +0700 от Evgeny Odegov <oev-racket at sibmail.com>:
>In the example, the value is box and triggering occurs almost 
>immediately after set!.
>But in case of another kind of value, triggering doesn't occur or take 
>much longer.
>Why? (Or maybe I do something wrong?)
>
>> 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
>> ____________________
>>    Racket Users list:
>>  http://lists.racket-lang.org/users
>
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>


-- 
Roman Klochkov
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