Hi, I reviewed the fix for LUCENENET-106 and I see a couple of issues:
1. The implementation of WeakHashMap in SupportClass.cs has a bug in that it assumes all keys will have a unique HashCode. Although the chances of this occurring are *very* small, it cannot be guaranteed. A collision would mean that the cached value for one indexReader could be returned as cached value for another indexReader (using the way this class is used in Lucene as example) 2. This class attempts to be a complete port of the java.util.WeakHashMap, but: - A correct implementation is difficult to implement, and .Net does not have an equivalent of java.lang.ref.ReferenceQueue to accelerate the cleanup process. - Since the behaviour of the WeakHashMap is closely tied to the behaviour of the garbage collector, it is very difficult to test properly, if at all. - Lucene only uses the get(Object key) and put(K key, V value) methods - In Lucene, the keys are IndexReader instances. In normal use cases there will be only 1 IndexReader live, and perhaps another one if 'warming up' is used before switching IndexSearchers after an index update. - If this class is presented as a complete port of java.util.WeakHashMap, users might assume this is production quality code and copy/paste its code in their own projects. Any further bugs found might harm the credibility of the Lucene project, even if those sections are never used in Lucene. (e.g.: The collection returned by Keys might contain null values. There's no guarantee the GC won't intervene between the call to Cleanup and the calls to keys.Add(w.Key.Target). 3. Most support classes that are needed for the conversion of java to .Net are in the anonymous namespace, but this one is in Lucene.Net.Util. I would propose to keep the namespaces corresponding to the original java packages clean and either put all support classes in the anonymous namespace or in a Lucene.Net specific one (Lucene.Net.DotNetPort ?) (I see that George moved it already to SupportClass, thanks George!) I have been using the java version of Lucene in a project for a long time. For a new project that is currently under development, we will be using the .Net version. For now we are using the 2.1 version using a custom patch to avoid the memory leak problem. I'll post an up to date version of this patch as a replacement for the current implementation of Lucene.Net.Util.WeakHashMap sometime next week... - It doesn't try to be a complete implementation of WeakHashMap: only the methods strictly necessary are implemented, all other methods throw a NotImplementedException. (It should probably be renamed to SimplifiedWeakHashMap or something) - It's optimized for the 'low number of keys' case. - It's simple code, but I want to test it thoroughly first. The original patch was put directly in the FieldCacheImpl code, I want to make sure I didn't make some stupid mistake while converting it. I have an account on Jira, but I don't have rights to reopen the issue... Regards, Luc -----Original Message----- From: Digy (JIRA) [mailto:j...@apache.org] Sent: zaterdag 27 december 2008 19:47 To: lucene-net-dev@incubator.apache.org Subject: [jira] Closed: () Lucene.NET (Revision: 603121) is leaking memory [ https://issues.apache.org/jira/browse/LUCENENET-106?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Digy closed LUCENENET-106. -------------------------- Resolution: Fixed Assignee: Digy Patches are applied. DIGY. > Lucene.NET (Revision: 603121) is leaking memory > ----------------------------------------------- > > Key: LUCENENET-106 > URL: https://issues.apache.org/jira/browse/LUCENENET-106 > Project: Lucene.Net > Issue Type: Bug > Environment: .NET 2.0 > Reporter: Anton K. > Assignee: Digy > Priority: Critical > Attachments: DIGY-FieldCacheImpl.patch, Digy.rar, > luceneSrc_memUsage.patch, Paches for v2.3.1.rar, > WeakHashTable+FieldCacheImpl.rar, WeakReferences.rar > > > readerCache Hashtable field (see FieldCacheImpl.cs) never releases some hash > items that have closed IndexReader object as a key. So a lot of Term > instances are never released. > Java version of Lucene uses WeakHashMap and therefore doesn't have this > problem. > This bug can be reproduced only when Sort functionality used during search. > See following link for additional information. > http://www.gossamer-threads.com/lists/lucene/java-user/55681 > Steps to reproduce: > 1)Create index > 2) Modify index by IndexWiter; Close IndexWriter > 3) Use IndexSearcher for searching with Sort; Close InexSearcher > 4) Go to step 2 > You'll get OutOfMemoryException after some time of running this algorithm. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.
