GenericObjectPool

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org.apache.commons.pool.impl
Class GenericObjectPool

java.lang.Object
  org.apache.commons.pool.BaseObjectPool
      org.apache.commons.pool.impl.GenericObjectPool

All Implemented Interfaces:: org.apache.commons.pool.ObjectPool

public class GenericObjectPool
extends org.apache.commons.pool.BaseObjectPool
implements org.apache.commons.pool.ObjectPool

A configurable org.apache.commons.pool.ObjectPool implementation.

When coupled with the appropriate org.apache.commons.pool.PoolableObjectFactory, GenericObjectPool provides robust pooling functionality for arbitrary objects.

A GenericObjectPool provides a number of configurable parameters:

maxActive 55 controls the maximum number of objects that can be borrowed from the pool at one time. When non-positive, there is no limit to the number of objects that may be active at one time. When maxActive 55 is exceeded, the pool is said to be exhausted.
maxIdle 55 controls the maximum number of objects that can sit idle in the pool at any time. When negative, there is no limit to the number of objects that may be idle at one time.
whenExhaustedAction 55 specifies the behaviour of the borrowObject() 55 method when the pool is exhausted:
- When whenExhaustedAction 55 is WHEN_EXHAUSTED_FAIL 55 , borrowObject() 55 will throw a java.util.NoSuchElementException
- When whenExhaustedAction 55 is WHEN_EXHAUSTED_GROW 55 , borrowObject() 55 will create a new object and return it(essentially making maxActive 55 meaningless.)
- When whenExhaustedAction 55 is WHEN_EXHAUSTED_BLOCK 55 , borrowObject() 55 will block (invoke Object.wait()>Object.wait() 55 until a new or idle object is available. If a positive maxWait 55 value is supplied, the borrowObject() 55 will block for at most that many milliseconds, after which a java.util.NoSuchElementException will be thrown. If maxWait 55 is non-positive, the borrowObject() 55 method will block indefinitely.
When testOnBorrow 55 is set, the pool will attempt to validate each object before it is returned from the borrowObject() 55 method. (Using the provided factory's PoolableObjectFactory.validateObject(java.lang.Object)>PoolableObjectFactory.validateObject(java.lang.Object) 55 method.) Objects that fail to validate will be dropped from the pool, and a different object will be borrowed.
When testOnReturn 55 is set, the pool will attempt to validate each object before it is returned to the pool in the returnObject(java.lang.Object) 55 method. (Using the provided factory's PoolableObjectFactory.validateObject(java.lang.Object)>PoolableObjectFactory.validateObject(java.lang.Object) 55 method.) Objects that fail to validate will be dropped from the pool.

Optionally, one may configure the pool to examine and possibly evict objects as they sit idle in the pool. This is performed by an "idle object eviction" thread, which runs asychronously. The idle object eviction thread may be configured using the following attributes:

timeBetweenEvictionRunsMillis 55 indicates how long the eviction thread should sleep before "runs" of examining idle objects. When non-positive, no eviction thread will be launched.
minEvictableIdleTimeMillis 55 specifies the minimum amount of time that an object may sit idle in the pool before it is eligable for eviction due to idle time. When non-positive, no object will be dropped from the pool due to idle time alone.
testWhileIdle 55 indicates whether or not idle objects should be validated using the factory's PoolableObjectFactory.validateObject(java.lang.Object)>PoolableObjectFactory.validateObject(java.lang.Object) 55 method. Objects that fail to validate will be dropped from the pool.

GenericObjectPool is not usable without a org.apache.commons.pool.PoolableObjectFactory. A non-null factory must be provided either as a constructor argument or via a call to setFactory(org.apache.commons.pool.PoolableObjectFactory) 55 before the pool is used.

Version:: $Revision: 1.32 $ $Date: 2004/04/27 20:15:56 $

Nested Class Summary

static class GenericObjectPool.Config
          A simple "struct" encapsulating the configuration information for a GenericObjectPool.

(package private) class GenericObjectPool.Evictor
          The idle object evictor thread.

(package private) class GenericObjectPool.ObjectTimestampPair
          A simple "struct" encapsulating an object instance and a timestamp.

Field Summary

private org.apache.commons.collections.CursorableLinkedList.Cursor _evictionCursor


private GenericObjectPool.Evictor _evictor
          My idle object eviction thread, if any.

private org.apache.commons.pool.PoolableObjectFactory _factory
          My org.apache.commons.pool.PoolableObjectFactory.

private int _maxActive
          The cap on the total number of active instances from the pool.

private int _maxIdle
          The cap on the number of idle instances in the pool.

private long _maxWait
          The maximum amount of time (in millis) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 .

private long _minEvictableIdleTimeMillis
          The minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any).

private int _minIdle
          The cap on the minimum number of idle instances in the pool.

private int _numActive
          The number of objects borrowObject() 55 borrowed from the pool, but not yet returned.

private int _numTestsPerEvictionRun
          The number of objects to examine during each run of the idle object evictor thread (if any).

private org.apache.commons.collections.CursorableLinkedList _pool
          My pool.

private boolean _testOnBorrow
          When true, objects will be validated 55 before being returned by the borrowObject() 55 method.

private boolean _testOnReturn
          When true, objects will be validated 55 before being returned to the pool within the returnObject(java.lang.Object) 55 .

private boolean _testWhileIdle
          When true, objects will be validated 55 by the idle object evictor (if any).

private long _timeBetweenEvictionRunsMillis
          The number of milliseconds to sleep between runs of the idle object evictor thread.

private byte _whenExhaustedAction
          The action to take when the borrowObject() 55 method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).

static int DEFAULT_MAX_ACTIVE
          The default cap on the total number of active instances from the pool.

static int DEFAULT_MAX_IDLE
          The default cap on the number of "sleeping" instances in the pool.

static long DEFAULT_MAX_WAIT
          The default maximum amount of time (in millis) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 .

static long DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS
          The default value for getMinEvictableIdleTimeMillis() 55 .

static int DEFAULT_MIN_IDLE
          The default minimum number of "sleeping" instances in the pool before before the evictor thread (if active) spawns new objects.

static int DEFAULT_NUM_TESTS_PER_EVICTION_RUN
          The default number of objects to examine per run in the idle object evictor.

static boolean DEFAULT_TEST_ON_BORROW
          The default "test on borrow" value.

static boolean DEFAULT_TEST_ON_RETURN
          The default "test on return" value.

static boolean DEFAULT_TEST_WHILE_IDLE
          The default "test while idle" value.

static long DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS
          The default "time between eviction runs" value.

static byte DEFAULT_WHEN_EXHAUSTED_ACTION
          The default "when exhausted action" for the pool.

static byte WHEN_EXHAUSTED_BLOCK
          A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should block until a new object is available, or the maximum wait time 55 has been reached.

static byte WHEN_EXHAUSTED_FAIL
          A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should fail, throwing a java.util.NoSuchElementException.

static byte WHEN_EXHAUSTED_GROW
          A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should simply create a new object anyway.

Fields inherited from class org.apache.commons.pool.BaseObjectPool

Constructor Summary

GenericObjectPool()
          Create a new GenericObjectPool.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, GenericObjectPool.Config config)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, boolean testOnBorrow, boolean testOnReturn)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, int maxIdle)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, int maxIdle, boolean testOnBorrow, boolean testOnReturn)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, int maxIdle, boolean testOnBorrow, boolean testOnReturn, long timeBetweenEvictionRunsMillis, int numTestsPerEvictionRun, long minEvictableIdleTimeMillis, boolean testWhileIdle)
          Create a new GenericObjectPool using the specified values.

GenericObjectPool(org.apache.commons.pool.PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, int maxIdle, int minIdle, boolean testOnBorrow, boolean testOnReturn, long timeBetweenEvictionRunsMillis, int numTestsPerEvictionRun, long minEvictableIdleTimeMillis, boolean testWhileIdle)
          Create a new GenericObjectPool using the specified values.

Method Summary

void addObject()
          Create an object, and place it into the pool.

private void addObjectToPool(java.lang.Object obj, boolean decrementNumActive)


java.lang.Object borrowObject()
          Obtain an instance from my pool.

private int calculateDeficit()


void clear()
          Clears any objects sitting idle in the pool, releasing any associated resources (optional operation).

void close()
          Close this pool, and free any resources associated with it.

(package private) java.lang.String debugInfo()


private void ensureMinIdle()
          Check to see if we are below our minimum number of objects if so enough to bring us back to our minimum.

void evict()


int getMaxActive()
          Returns the cap on the total number of active instances from my pool.

int getMaxIdle()
          Returns the cap on the number of "idle" instances in the pool.

long getMaxWait()
          Returns the maximum amount of time (in milliseconds) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 .

long getMinEvictableIdleTimeMillis()
          Returns the minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any).

int getMinIdle()
          Returns the minimum number of objects allowed in the pool before the evictor thread (if active) spawns new objects.

int getNumActive()
          Return the number of instances currently borrowed from my pool (optional operation).

int getNumIdle()
          Return the number of instances currently idle in my pool (optional operation).

private int getNumTests()


int getNumTestsPerEvictionRun()
          Returns the number of objects to examine during each run of the idle object evictor thread (if any).

boolean getTestOnBorrow()
          When true, objects will be validated 55 before being returned by the borrowObject() 55 method.

boolean getTestOnReturn()
          When true, objects will be validated 55 before being returned to the pool within the returnObject(java.lang.Object) 55 .

boolean getTestWhileIdle()
          When true, objects will be validated 55 by the idle object evictor (if any).

long getTimeBetweenEvictionRunsMillis()
          Returns the number of milliseconds to sleep between runs of the idle object evictor thread.

byte getWhenExhaustedAction()
          Returns the action to take when the borrowObject() 55 method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).

void invalidateObject(java.lang.Object obj)
          Invalidates an object from the pool By contract, obj MUST have been obtained using borrowObject 55 or a related method as defined in an implementation or sub-interface.

void returnObject(java.lang.Object obj)
          Return an instance to my pool.

void setConfig(GenericObjectPool.Config conf)
          Sets my configuration.

void setFactory(org.apache.commons.pool.PoolableObjectFactory factory)
          Sets the factory I use to create new instances (optional operation).

void setMaxActive(int maxActive)
          Sets the cap on the total number of active instances from my pool.

void setMaxIdle(int maxIdle)
          Sets the cap on the number of "idle" instances in the pool.

void setMaxWait(long maxWait)
          Sets the maximum amount of time (in milliseconds) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 .

void setMinEvictableIdleTimeMillis(long minEvictableIdleTimeMillis)
          Sets the minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any).

void setMinIdle(int minIdle)
          Sets the minimum number of objects allowed in the pool before the evictor thread (if active) spawns new objects.

void setNumTestsPerEvictionRun(int numTestsPerEvictionRun)
          Sets the number of objects to examine during each run of the idle object evictor thread (if any).

void setTestOnBorrow(boolean testOnBorrow)
          When true, objects will be validated 55 before being returned by the borrowObject() 55 method.

void setTestOnReturn(boolean testOnReturn)
          When true, objects will be validated 55 before being returned to the pool within the returnObject(java.lang.Object) 55 .

void setTestWhileIdle(boolean testWhileIdle)
          When true, objects will be validated 55 by the idle object evictor (if any).

void setTimeBetweenEvictionRunsMillis(long timeBetweenEvictionRunsMillis)
          Sets the number of milliseconds to sleep between runs of the idle object evictor thread.

void setWhenExhaustedAction(byte whenExhaustedAction)
          Sets the action to take when the borrowObject() 55 method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).

protected void startEvictor(long delay)
          Start the eviction thread or service, or when delay is non-positive, stop it if it is already running.

Methods inherited from class org.apache.commons.pool.BaseObjectPool

assertOpen, isClosed

Methods inherited from class java.lang.Object

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

Field Detail

WHEN_EXHAUSTED_FAIL

public static final byte WHEN_EXHAUSTED_FAIL

A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should fail, throwing a java.util.NoSuchElementException.

See Also:: WHEN_EXHAUSTED_BLOCK 55 , WHEN_EXHAUSTED_GROW 55 , setWhenExhaustedAction(byte) 55 , Constant Field Values

WHEN_EXHAUSTED_BLOCK

public static final byte WHEN_EXHAUSTED_BLOCK

A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should block until a new object is available, or the maximum wait time 55 has been reached.

See Also:: WHEN_EXHAUSTED_FAIL 55 , WHEN_EXHAUSTED_GROW 55 , setMaxWait(long) 55 , getMaxWait() 55 , setWhenExhaustedAction(byte) 55 , Constant Field Values

WHEN_EXHAUSTED_GROW

public static final byte WHEN_EXHAUSTED_GROW

A "when exhausted action" type indicating that when the pool is exhausted (i.e., the maximum number of active objects has been reached), the borrowObject() 55 method should simply create a new object anyway.

See Also:: WHEN_EXHAUSTED_FAIL 55 , WHEN_EXHAUSTED_GROW 55 , setWhenExhaustedAction(byte) 55 , Constant Field Values

DEFAULT_MAX_IDLE

public static final int DEFAULT_MAX_IDLE

The default cap on the number of "sleeping" instances in the pool.

See Also:: getMaxIdle() 55 , setMaxIdle(int) 55 , Constant Field Values

DEFAULT_MIN_IDLE

public static final int DEFAULT_MIN_IDLE

The default minimum number of "sleeping" instances in the pool before before the evictor thread (if active) spawns new objects.

See Also:: getMinIdle() 55 , setMinIdle(int) 55 , Constant Field Values

DEFAULT_MAX_ACTIVE

public static final int DEFAULT_MAX_ACTIVE

The default cap on the total number of active instances from the pool.

See Also:: getMaxActive() 55 , Constant Field Values

DEFAULT_WHEN_EXHAUSTED_ACTION

public static final byte DEFAULT_WHEN_EXHAUSTED_ACTION

The default "when exhausted action" for the pool.

See Also:: WHEN_EXHAUSTED_BLOCK 55 , WHEN_EXHAUSTED_FAIL 55 , WHEN_EXHAUSTED_GROW 55 , setWhenExhaustedAction(byte) 55 , Constant Field Values

DEFAULT_MAX_WAIT

public static final long DEFAULT_MAX_WAIT

The default maximum amount of time (in millis) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 .

See Also:: getMaxWait() 55 , setMaxWait(long) 55 , Constant Field Values

DEFAULT_TEST_ON_BORROW

public static final boolean DEFAULT_TEST_ON_BORROW

The default "test on borrow" value.

See Also:: getTestOnBorrow() 55 , setTestOnBorrow(boolean) 55 , Constant Field Values

DEFAULT_TEST_ON_RETURN

public static final boolean DEFAULT_TEST_ON_RETURN

The default "test on return" value.

See Also:: getTestOnReturn() 55 , setTestOnReturn(boolean) 55 , Constant Field Values

DEFAULT_TEST_WHILE_IDLE

public static final boolean DEFAULT_TEST_WHILE_IDLE

The default "test while idle" value.

See Also:: getTestWhileIdle() 55 , setTestWhileIdle(boolean) 55 , getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55 , Constant Field Values

DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS

public static final long DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS

The default "time between eviction runs" value.

See Also:: getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55 , Constant Field Values

DEFAULT_NUM_TESTS_PER_EVICTION_RUN

public static final int DEFAULT_NUM_TESTS_PER_EVICTION_RUN

The default number of objects to examine per run in the idle object evictor.

See Also:: getNumTestsPerEvictionRun() 55 , setNumTestsPerEvictionRun(int) 55 , getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55 , Constant Field Values

DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS

public static final long DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS

The default value for getMinEvictableIdleTimeMillis() 55 .

See Also:: getMinEvictableIdleTimeMillis() 55 , setMinEvictableIdleTimeMillis(long) 55 , Constant Field Values

_maxIdle

private int _maxIdle

The cap on the number of idle instances in the pool.

See Also:: setMaxIdle(int) 55 , getMaxIdle() 55

_minIdle

private int _minIdle

The cap on the minimum number of idle instances in the pool.

See Also:: setMinIdle(int) 55 , getMinIdle() 55

_maxActive

private int _maxActive

The cap on the total number of active instances from the pool.

See Also:: setMaxActive(int) 55 , getMaxActive() 55

_maxWait

private long _maxWait

The maximum amount of time (in millis) the borrowObject() 55 method should block before throwing an exception when the pool is exhausted and the "when exhausted" action 55 is WHEN_EXHAUSTED_BLOCK 55 . When less than 0, the borrowObject() 55 method may block indefinitely.

See Also:: setMaxWait(long) 55 , getMaxWait() 55 , WHEN_EXHAUSTED_BLOCK 55 , setWhenExhaustedAction(byte) 55 , getWhenExhaustedAction() 55

_whenExhaustedAction

private byte _whenExhaustedAction

The action to take when the borrowObject() 55 method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).

See Also:: WHEN_EXHAUSTED_BLOCK 55 , WHEN_EXHAUSTED_FAIL 55 , WHEN_EXHAUSTED_GROW 55 , DEFAULT_WHEN_EXHAUSTED_ACTION 55 , setWhenExhaustedAction(byte) 55 , getWhenExhaustedAction() 55

_testOnBorrow

private boolean _testOnBorrow

When true, objects will be validated 55 before being returned by the borrowObject() 55 method. If the object fails to validate, it will be dropped from the pool, and we will attempt to borrow another.

See Also:: setTestOnBorrow(boolean) 55 , getTestOnBorrow() 55

_testOnReturn

private boolean _testOnReturn

When true, objects will be validated 55 before being returned to the pool within the returnObject(java.lang.Object) 55 .

See Also:: getTestOnReturn() 55 , setTestOnReturn(boolean) 55

_testWhileIdle

private boolean _testWhileIdle

When true, objects will be validated 55 by the idle object evictor (if any). If an object fails to validate, it will be dropped from the pool.

See Also:: setTestWhileIdle(boolean) 55 , getTestWhileIdle() 55 , getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55

_timeBetweenEvictionRunsMillis

private long _timeBetweenEvictionRunsMillis

The number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.

See Also:: setTimeBetweenEvictionRunsMillis(long) 55 , getTimeBetweenEvictionRunsMillis() 55

_numTestsPerEvictionRun

private int _numTestsPerEvictionRun

The number of objects to examine during each run of the idle object evictor thread (if any).

When a negative value is supplied, ceil(getNumIdle() 55 )/abs(getNumTestsPerEvictionRun() 55 ) tests will be run. I.e., when the value is -n, roughly one nth of the idle objects will be tested per run.

See Also:: setNumTestsPerEvictionRun(int) 55 , getNumTestsPerEvictionRun() 55 , getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55

_minEvictableIdleTimeMillis

private long _minEvictableIdleTimeMillis

The minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any). When non-positive, no objects will be evicted from the pool due to idle time alone.

See Also:: setMinEvictableIdleTimeMillis(long) 55 , getMinEvictableIdleTimeMillis() 55 , getTimeBetweenEvictionRunsMillis() 55 , setTimeBetweenEvictionRunsMillis(long) 55

_pool

private org.apache.commons.collections.CursorableLinkedList _pool

My pool.

_factory

private org.apache.commons.pool.PoolableObjectFactory _factory

My org.apache.commons.pool.PoolableObjectFactory.

_numActive

private int _numActive

The number of objects borrowObject() 55 borrowed from the pool, but not yet returned.

_evictor

private GenericObjectPool.Evictor _evictor

My idle object eviction thread, if any.

_evictionCursor

private org.apache.commons.collections.CursorableLinkedList.Cursor _evictionCursor

Constructor Detail

GenericObjectPool

public GenericObjectPool()

Create a new GenericObjectPool.