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Subject: Re: Design thought for callbacks
From: Cem Karan <cfkaran2@gmail.com>
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Date: Sun, 22 Feb 2015 08:42:10 -0500
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On Feb 22, 2015, at 7:12 AM, Marko Rauhamaa <marko@pacujo.net> wrote:

> Cem Karan <cfkaran2@gmail.com>:
>=20
>> On Feb 21, 2015, at 11:03 AM, Marko Rauhamaa <marko@pacujo.net> =
wrote:
>>> I use callbacks all the time but haven't had any problems with =
strong
>>> references.
>>>=20
>>> I am careful to move my objects to a zombie state after they're done =
so
>>> they can absorb any potential loose callbacks that are lingering in =
the
>>> system.
>>=20
>> So, if I were designing a library for you, you would be willing to =
have
>> a 'zombie' attribute on your callback, correct? This would allow the
>> library to query its callbacks to ensure that only 'live' callbacks =
are
>> called. How would you handle closures?
>=20
> Sorry, don't understand the question.

You were saying that you move your objects into a zombie state.  I =
assumed that you meant you marked them in some manner (e.g., setting =
'is_zombie' to True), so that anything that has a strong reference to =
the object knows the object is not supposed to be used anymore.  That =
way, regardless of where or how many times you've registered your object =
for callbacks, the library can do something like the following (banged =
out in my mail application, may have typos):

"""
_CALLBACKS =3D []

def execute_callbacks():
    global _CALLBACKS
    _CALLBACKS =3D [x for x in _CALLBACKS if not x.is_zombie]
    for x in _CALLBACKS:
        x()
"""

That will lazily unregister callbacks that are in the zombie state, =
which will eventually lead to their collection by the garbage collector. =
 It won't work for anything that you don't have a reference for =
(lambdas, etc.), but it should work in a lot of cases.

Is this what you meant?

Thanks,
Cem Karan=