Package org.apache.hadoop.hbase.util

Class ObjectPool<K,V>

java.lang.Object

org.apache.hadoop.hbase.util.ObjectPool<K,V>

Direct Known Subclasses:

SoftObjectPool, WeakObjectPool

@Private
public abstract class ObjectPool<K,V>
extends Object

A thread-safe shared object pool in which object creation is expected to be lightweight, and the objects may be excessively created and discarded.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	ObjectPool.ObjectFactory<K,V>	An ObjectFactory object is used to create new shared objects on demand.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_CONCURRENCY_LEVEL	The default concurrency level, used when not otherwise specified in a constructor.
static final int	DEFAULT_INITIAL_CAPACITY	The default initial capacity, used when not otherwise specified in a constructor.
private final ObjectPool.ObjectFactory<K,V>	objectFactory
private final Lock	purgeLock	For preventing parallel purge
protected final ConcurrentMap<K,Reference<V>>	referenceCache	Does not permit null keys.
protected final ReferenceQueue<V>	staleRefQueue

Constructor Summary

Constructors

Constructor	Description
ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory)	Creates a new pool with the default initial capacity (16) and the default concurrency level (16).
ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory, int initialCapacity)	Creates a new pool with the given initial capacity and the default concurrency level (16).
ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory, int initialCapacity, int concurrencyLevel)	Creates a new pool with the given initial capacity and the given concurrency level.

Method Summary

Modifier and Type	Method	Description
abstract Reference<V>	createReference(K key, V obj)	Create a reference associated with the given object
V	get(K key)	Returns a shared object associated with the given key, which is identified by the equals method.
abstract K	getReferenceKey(Reference<V> ref)	Get key of the given reference
void	purge()	Removes stale references of shared objects from the pool.
int	size()	Returns an estimated count of objects kept in the pool.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

staleRefQueue

protected final ReferenceQueue<V> staleRefQueue

objectFactory

private final ObjectPool.ObjectFactory<K,V> objectFactory

referenceCache

protected final ConcurrentMap<K,Reference<V>> referenceCache

Does not permit null keys.

purgeLock

private final Lock purgeLock

For preventing parallel purge

DEFAULT_INITIAL_CAPACITY

public static final int DEFAULT_INITIAL_CAPACITY

The default initial capacity, used when not otherwise specified in a constructor.

See Also:

• Constant Field Values

DEFAULT_CONCURRENCY_LEVEL

public static final int DEFAULT_CONCURRENCY_LEVEL

The default concurrency level, used when not otherwise specified in a constructor.

See Also:

• Constant Field Values

Constructor Details

ObjectPool

public ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory)

Creates a new pool with the default initial capacity (16) and the default concurrency level (16).

Parameters:

objectFactory - the factory to supply new objects on demand

Throws:

NullPointerException - if objectFactory is null

ObjectPool

public ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory,
 int initialCapacity)

Creates a new pool with the given initial capacity and the default concurrency level (16).

Parameters:

objectFactory - the factory to supply new objects on demand

initialCapacity - the initial capacity to keep objects in the pool

Throws:

NullPointerException - if objectFactory is null

IllegalArgumentException - if initialCapacity is negative

ObjectPool

public ObjectPool(ObjectPool.ObjectFactory<K,V> objectFactory,
 int initialCapacity,
 int concurrencyLevel)

Creates a new pool with the given initial capacity and the given concurrency level.

Parameters:

objectFactory - the factory to supply new objects on demand

initialCapacity - the initial capacity to keep objects in the pool

concurrencyLevel - the estimated count of concurrently accessing threads

Throws:

NullPointerException - if objectFactory is null

IllegalArgumentException - if initialCapacity is negative or concurrencyLevel is non-positive

Method Details

purge

public void purge()

Removes stale references of shared objects from the pool. References newly becoming stale may still remain.

The implementation of this method is expected to be lightweight when there is no stale reference with the Oracle (Sun) implementation of ReferenceQueue, because ReferenceQueue.poll just checks a volatile instance variable in ReferenceQueue.

createReference

public abstract Reference<V> createReference(K key,
 V obj)

Create a reference associated with the given object

Parameters:

key - the key to store in the reference

obj - the object to associate with

Returns:

the reference instance

getReferenceKey

public abstract K getReferenceKey(Reference<V> ref)

Get key of the given reference

Parameters:

ref - The reference

Returns:

key of the reference

get

public V get(K key)

Returns a shared object associated with the given key, which is identified by the equals method.

Throws:

NullPointerException - if key is null

size

public int size()

Returns an estimated count of objects kept in the pool. This also counts stale references, and you might want to call purge() beforehand.