CloseableThreadLocal memory leak in LocalDataStoreSlot (with workaround)
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Key: LUCENENET-358
URL: https://issues.apache.org/jira/browse/LUCENENET-358
Project: Lucene.Net
Issue Type: Bug
Environment: Microsoft WIndows Server 2008 Enterprise x64. SP2.
.NET Framework 4.0
Reporter: Rezgar Cadro
Priority: Critical
Attachments: CloseableThreadLocal MemoryLeak.patch
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
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