Package org.apache.lucene.util
Class CloseableThreadLocal<T>
- java.lang.Object
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- org.apache.lucene.util.CloseableThreadLocal<T>
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- All Implemented Interfaces:
java.io.Closeable
,java.lang.AutoCloseable
public class CloseableThreadLocal<T> extends java.lang.Object implements java.io.Closeable
Java's builtin ThreadLocal has a serious flaw: it can take an arbitrarily long amount of time to dereference the things you had stored in it, even once the ThreadLocal instance itself is no longer referenced. This is because there is single, master map stored for each thread, which all ThreadLocals share, and that master map only periodically purges "stale" entries.While not technically a memory leak, because eventually the memory will be reclaimed, it can take a long time and you can easily hit OutOfMemoryError because from the GC's standpoint the stale entries are not reclaimable.
This class works around that, by only enrolling WeakReference values into the ThreadLocal, and separately holding a hard reference to each stored value. When you call
close()
, these hard references are cleared and then GC is freely able to reclaim space by objects stored in it.We can not rely on
ThreadLocal.remove()
as it only removes the value for the caller thread, whereasclose()
takes care of all threads. You should not callclose()
until all threads are done using the instance.
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Field Summary
Fields Modifier and Type Field Description private java.util.concurrent.atomic.AtomicInteger
countUntilPurge
private java.util.Map<java.lang.Thread,T>
hardRefs
private static int
PURGE_MULTIPLIER
private java.lang.ThreadLocal<java.lang.ref.WeakReference<T>>
t
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Constructor Summary
Constructors Constructor Description CloseableThreadLocal()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
close()
T
get()
protected T
initialValue()
private void
maybePurge()
private void
purge()
void
set(T object)
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Method Detail
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initialValue
protected T initialValue()
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get
public T get()
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set
public void set(T object)
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maybePurge
private void maybePurge()
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purge
private void purge()
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close
public void close()
- Specified by:
close
in interfacejava.lang.AutoCloseable
- Specified by:
close
in interfacejava.io.Closeable
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