From: Eric Hodel <drbrain@...7.net>
Date: 2005-04-13T16:43:48+09:00
Subject: Re: ability to run finalizers at a given point of a program?

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On 13 Apr 2005, at 00:28, Guillaume Cottenceau wrote:

>> So, I am getting the same result ts was getting.
>
> Now that is strange.. :/
>
>>> What difference do you pretend your program is making with mine?
>>
>> The difference is in this:
>>
>> (your version):
>> def scopeme
>>     foo = Foo.new
>>     ObjectSpace.define_finalizer(foo, proc { puts "*** 
>> pseudo-destructor" })
>> end
>>
>> That block captures foo as well. As a result, that instance will never
>> be unreferenced, and thus never going to be GC'ed until the program
>> ends.
>>
>> OTOH, ts' version:
>> class Foo
>>    def self.final
>>       proc { puts "*** pseudo-destructor" }
>>    end
>> end
>>
>> def scopeme
>>    foo = Foo.new
>>    ObjectSpace.define_finalizer(foo, Foo.final)
>> end
>>
>> Notice that the finalizer block does not capture the Foo instance.
>
> Wait.. both calls to define_finalizer have a reference to foo as the
> first argument, and both have a closure as second argument which
> doesn't have a reference to foo.

Incorrect.  The first argument is irrelevant.  
ObjectSpace::define_finalizer is written this way probably to make 
things ugly.  You have to pass in the object you wish to attach a 
finalizer to, and that's what the first arg is for.

In your version, foo is in-scope when the finalizer proc is created, so 
the proc captures foo *even though it is not explicitly used in the 
proc*.  That's right!  Just because you don't reference foo inside a 
closure doesn't mean it magically disappears for you.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
FEC2 57F1 D465 EB15 5D6E  7C11 332A 551C 796C 9F04

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