[IronPython] Possible bug in Ipy 2.6.1 WeakDictionary

Dino Viehland dinov at microsoft.com
Mon Oct 4 19:22:24 CEST 2010

Nope, you have it right - this is fixed in the Main branch and internally it's fixed in the 2.6 branch as well (There was a report about this from some internal uses of IronPython).    Unfortunately it looks like the fix hasn't propagated out to the 2.6 branch on CodePlex for some reason.  I'll try and figure out what's going on there but either way it'll be fixed in the next set of releases.  If you want to build from source you can just add a call to CheckCleanup(); in there before the dict[new WeakObject(...)] = ...  assignment.

From: users-bounces at lists.ironpython.com [mailto:users-bounces at lists.ironpython.com] On Behalf Of Idan Zaltzberg
Sent: Monday, October 04, 2010 9:02 AM
To: Discussion of IronPython
Subject: [IronPython] Possible bug in Ipy 2.6.1 WeakDictionary

I'm investigating memory leakage in a Ipy 2.6.1 application.
Using WinDbg I found a WeakDictionary that is only increasing in size, though most of the instances are already collected.
This WeakDicitionary is used by a DelegationInfo object.

Looking at the code, I think I found the problem:
The method CheckCleanup is called the method "public void Add(TKey key, TValue value)"
But it NOT called from the indexer:

public TValue this[TKey key] {
            get {
                return dict[key];
            set {
                // If the WeakHash already holds this value as a key, it will lead to a circular-reference and result
                // in the objects being kept alive forever. The caller needs to ensure that this cannot happen.

                dict[new WeakObject(key)] = value;

Since the dictionary is populated using the indexer in DelegateInfo:
_constantMap[target] = new WeakReference(clone = (object[])_constants.Clone());

This means that the "version" field is never updated, and the dictionary never gets cleaned up.

Have I got something wrong here?
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