On 23 September 2010 23:58, Andreas Raab andreas.raab@gmx.de wrote:
Isn't that a bit of a made-up problem? I've never seen (nor heard of) anyone even trying to attach more than one finalizer to an object. Disallowing it could be done, but unless there's a good reason for it I'm not in favor of deciding what is good policy and what isn't without a practical use case at hand. If you have a use-case I'd like to hear more about it, but if not, then *shrug*, who cares :-)
The practical use, that one may mistakenly add two same finalizers on a same object, like closing a file handle, or free external memory. And it is potentially dangerous, because OS could reuse the same memory location or file handle, once you closed it, so, by closing it twice you can get a serious trouble finding what's going on.
My point, that if one ever needs a composite finalization action, a WeakRegistry is wrong place for that. WeakRegistry should prevent registering more than a signle finalizer per unique object to prevent potential problems which could arise from such composition(s).
Cheers, - Andreas
On 9/23/2010 1:23 PM, Igor Stasenko wrote:
Hello,
i'd like to raise this subject once more, because i don't like it (or don't understand?).
In all scenarios, where i met the need to use finalization, a single finalizer is sufficient. Moreover, there is always a single object who controls a weak reference, and it never leaks it out, to prevent the case, when some other object may obtain a strong reference on it, making it permanently held in object memory.
Multiple different finalizers for single object, from design point of view, means that you having two different, not related frameworks, which using same object, and want to do something when it dies. A scenario, where its possible and userful, still don't comes into my mind. In contrary, whenever i see a use of finalizers, its in most cases about graceful control over external resource, such as:
- file
- socket
- external memory
and i really don't see how multiple finalizers per single resource could do any good.
Suppose one finalizer closing a file handle, while another one flushing it buffer cache. Now, how you going to ensure, that one finalizer will execute first, before another one? And what if third framework comes into play and wants to add another finalizer on top of that, which should do something in the middle between flushing a cache and closing file handle?
From the above, the only conclusion can be made: use a single
finalizer, and put all logic& operation ordering into it. And also, prevent leakage of object pointer (such as file handle) outside of your model, otherwise it may cause harm.
That's why i think a current WeakRegistry model provoking bad design practices. I think a better behavior would be to raise an error, if something wants to register finalizer twice for a single object.