Garbage Collector

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Guest

Hey everyone,

i'm currently trying to implement a WeakDictionary, where all keys are
WeakReferences. Now I want to remove the keys when the targets are no longer
reachable. Is there any possibility to get informed when an object is garbage
collected?

Greetings

Heiko Böttger
 
Is there any possibility to get informed when an object is garbage collected?

No, there's no such notification in managed code.


Mattias
 
Thank you for your answer.

Thats want I thought.
Click to expand...

I'm not sure if this is applicable, but if you control the objects being
garbage collected, you could add a finalizer who would notify some method
that it is about to get garbage collected. The garbage collector calls
the finalizer before collecting it unless the objects finalizer is
suppressed (typically in the Dispose method).
 
My solution was to check if the weak reference had lost its target to
the GC before returning it.

I also implemented a timed process which purged items that had been
GCed.

Tigger
 
Thank you for your answer.

I have already seen some examples on the net, they all make use of timers.
The problem with these solutions is that there is no collection containing
the GCed objects and I have to iterate through the whole list of
weakreferences. When you are dealing with long lists this isn't very fast. I
would prefere to setup something like a GC listener. In Java there is a
ReferenceQueue which is bound to several references. Whenever a weak
reference is set to null, ot is added to the queue. Since the queue contains
only the references pointing which objects where GCed. You can simple removed
them from your key list.



Tigger said:
My solution was to check if the weak reference had lost its target to
the GC before returning it.

I also implemented a timed process which purged items that had been
GCed.

Tigger
Click to expand...
 
I already thought about this solution, but as you mentioned the object have
to be under my control and wouldn't rely on this.
 
Heiko,

This is an excellent question. The only I way I know of would be to
add code to the finalizer, but like you said, if the object isn't under
your control then that will be impossible. What I did was everytime
something was added to the dictionary I called a Purge method that
would loop through items to find which ones were unreachable. In
hindsight that was probably a bad idea because inserts into my
dictionary now became O(n) instead of O(1), but I wasn't storing a lot
to begin with so it wasn't that big of an issue. Honestly, some
combination of purging on inserts and using a timer might be the best
you can do. Sad isn't it?

One tip...remember to write your own IEnumerator for your collection
and make sure you filter out unreachable objects.

Brian
 
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