[racket] Destructors in Racket

 Ready. Package `finalizer' on pkgs.racket-lang.org


Sat, 02 Aug 2014 21:12:50 +0400 от Roman Klochkov <kalimehtar at mail.ru>:
>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
>____________________
>  Racket Users list:
>   http://lists.racket-lang.org/users
>


-- 
Roman Klochkov
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