Details
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Bug
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Status: Resolved
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Critical
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Resolution: Fixed
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Lucene.Net 2.9.2, Lucene.Net 2.9.4, Lucene.Net 2.9.4g
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None
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Microsoft WIndows Server 2008 Enterprise x64. SP2.
.NET Framework 4.0
Description
Recently we have been suffering from a severe memory leak when executing intense open/close operations on IndexSearcher and IndexModifier.
Memory profiling showed that memory is being held by LocalDataStore[] objects.
After some digging, the root of the problem has been found in CloseableThreadLocal class:
private System.LocalDataStoreSlot t = System.Threading.Thread.AllocateDataSlot();
What we see is that every instantiated object of CloseableThreadLocal causes new data slot allocation performed for every thread.
Thread.AllocateDataSlot() does not simply allocate a new slot, replacing an old one, but enlarging an existing buffer in-thread, appending data to the end of internal LocalDataStore[] collection, which causes a severe memory leak .
As long as "t" variable is instantiated on every object creation, and (in current class implementation) every object is used by a single thread, replacing "private System.LocalDataStoreSlot t = System.Threading.Thread.AllocateDataSlot();" with simple "private object dataSlot;" and removing "hardRefs" Dictionary solves the problem and prevents memory leak.
We have tried to implement the expected behavior by using [ThreadStatic] attribute instead of LocalDataStoreSlot, but the attempt failed because of unexpected exceptions being thrown.
Patch can be found at Lucene.Net repository under