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.NET Forum / .NET Framework / New Users / October 2006Garbage Collector
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  SignatureMattias Sjögren [C# MVP] mattias @ mvps.org http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com Please reply only to the newsgroup. Thank you for your answer. Thats want I thought. > >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. > [quoted text clipped - 11 lines] >> http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com >> Please reply only to the newsgroup. 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). SignatureHappy Coding! Morten Wennevik [C# MVP] 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. > > [quoted text clipped - 17 lines] > the finalizer before collecting it unless the objects finalizer is > suppressed (typically in the Dispose method). 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. > My solution was to check if the weak reference had lost its target to > the GC before returning it. [quoted text clipped - 25 lines] > > the finalizer before collecting it unless the objects finalizer is > > suppressed (typically in the Dispose method). I already thought about this solution, but as you mentioned the object have to be under my control and wouldn't rely on this. > > Thank you for your answer. > > [quoted text clipped - 17 lines] > the finalizer before collecting it unless the objects finalizer is > suppressed (typically in the Dispose method). 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 > Hey everyone, > [quoted text clipped - 6 lines] > > Heiko Böttger Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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