GC object finalization not guaranteed

[Don]

Leandro Lucarella wrote:
> Robert Jacques, el 18 de abril a las 11:56 me escribiste:
>> On Sat, 18 Apr 2009 11:24:14 -0400, Leandro Lucarella <llucax at gmail.com> wrote:
>>> I've just found out[1] this[2]:
>>>
>>> 	The garbage collector is not guaranteed to run the destructor for
>>> 	all unreferenced objects.
>>>
>>> Is there any reason why D can't guarantee that all finalizers will be
>>> called, at least when the program ends?
>> Well, a couple of quick tests show that under normal situations (i.e.
>> normal program termination and termination from an exception) the
>> finalizers do run (D2). However, if a finalizer throws an exception,
>> then the rest of the finalizers aren't called. Also, if you call
>> std.c.stdlib.exit, the finalizers won't run.
> 
> Well, I'm not talking about experimentation, I'm talking about source code
> ;)
> 
> The current GC implementation don't call finalizers for data that's still
> reference when the program *ended* (this is allowed by the specs, so it's
> fine, the question is why it's allowed by the specs).

I don't understand why D even has finalizers. Can they do anything useful?