WeakObjectPool (Apache HBase 1.2.12 API)

java.lang.Object
- org.apache.hadoop.hbase.util.WeakObjectPool<K,V>

```
@InterfaceAudience.Private
public class WeakObjectPool<K,V>
extends Object
```
A WeakReference based shared object pool. The objects are kept in weak references and associated with keys which are identified by the equals method. The objects are created by WeakObjectPool.ObjectFactory on demand. The object creation is expected to be lightweight, and the objects may be excessively created and discarded. Thread safe.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static interface`	`WeakObjectPool.ObjectFactory<K,V>` An `ObjectFactory` object is used to create new shared objects on demand.
`private class`	`WeakObjectPool.ObjectReference`

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`DEFAULT_CONCURRENCY_LEVEL` The default concurrency level, used when not otherwise specified in a constructor.
`static int`	`DEFAULT_INITIAL_CAPACITY` The default initial capacity, used when not otherwise specified in a constructor.
`private WeakObjectPool.ObjectFactory<K,V>`	`objectFactory`
`private ConcurrentMap<K,WeakObjectPool.ObjectReference>`	`referenceCache` Does not permit null keys.
`private ReferenceQueue<V>`	`staleRefQueue`

Constructor Summary

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

Method Summary

Methods
Modifier and Type	Method and Description
`V`	`get(K key)` Returns a shared object associated with the given `key`, which is identified by the `equals` method.
`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 Detail
  - staleRefQueue
```
private final ReferenceQueue<V> staleRefQueue
```
  - objectFactory
```
private final WeakObjectPool.ObjectFactory<K,V> objectFactory
```
  - referenceCache
```
private final ConcurrentMap<K,WeakObjectPool.ObjectReference> referenceCache
```
    Does not permit null keys.
  - 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 Detail
  - WeakObjectPool
```
public WeakObjectPool(WeakObjectPool.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
  - WeakObjectPool
```
public WeakObjectPool(WeakObjectPool.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
  - WeakObjectPool
```
public WeakObjectPool(WeakObjectPool.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 Detail
  - 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.
  - 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.

Class WeakObjectPool<K,V>

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

staleRefQueue

objectFactory

referenceCache

DEFAULT_INITIAL_CAPACITY

DEFAULT_CONCURRENCY_LEVEL

Constructor Detail

WeakObjectPool

WeakObjectPool

WeakObjectPool

Method Detail

purge

get

size