org.apache.avalon.excalibur.pool
Class InstrumentedResourceLimitingPool

java.lang.Object
  extended byorg.apache.avalon.framework.logger.AbstractLogEnabled
      extended byorg.apache.avalon.excalibur.pool.InstrumentedResourceLimitingPool
All Implemented Interfaces:
Disposable, Instrumentable, LogEnabled, Pool, ThreadSafe
Direct Known Subclasses:
ValidatedResourceLimitingPool

public class InstrumentedResourceLimitingPool
extends AbstractLogEnabled
implements Pool, LogEnabled, Disposable, ThreadSafe, Instrumentable

General Pool implementation which supports; weak and strong pool size limits, optional blocking gets when poolables are not available, and automatic pool trimming of unused poolables.

Whenever get() is called, the pool tests to see whether it is time to trim old poolables from the pool. If any old poolables exist then they are removed at this time. This means that old poolables will not be removed if get() is never called. Applications can optionally call trim() to force old objects to be trimmed. See the trim() method for details of how trimming works.

Since:
4.1
Version:
CVS $Revision: 1.1 $ $Date: 2004/03/29 16:50:37 $
Author:
Avalon Development Team

Field Summary
static java.lang.String DEFAULT_INSTRUMENTABLE_NAME
           
static java.lang.String INSTRUMENT_BLOCKS_NAME
           
static java.lang.String INSTRUMENT_CREATES_NAME
           
static java.lang.String INSTRUMENT_DECOMMISSIONS_NAME
           
static java.lang.String INSTRUMENT_GETS_NAME
           
static java.lang.String INSTRUMENT_PUTS_NAME
           
static java.lang.String INSTRUMENT_READY_SIZE_NAME
           
static java.lang.String INSTRUMENT_SIZE_NAME
           
protected  java.lang.Object m_semaphore
          Object used to synchronize access to the get and put methods
 
Fields inherited from interface org.apache.excalibur.instrument.Instrumentable
EMPTY_INSTRUMENT_ARRAY, EMPTY_INSTRUMENTABLE_ARRAY
 
Constructor Summary
InstrumentedResourceLimitingPool(ObjectFactory factory, int max, boolean maxStrict, boolean blocking, long blockTimeout, long trimInterval)
          Creates a new InstrumentedResourceLimitingPool
 
Method Summary
 void dispose()
          The dispose operation is called at the end of a components lifecycle.
 Poolable get()
          Gets a Poolable from the pool.
 Instrumentable[] getChildInstrumentables()
          Any Object which implements Instrumentable can also make use of other Instrumentable child objects.
 java.lang.String getInstrumentableName()
          Gets the name of the Instrumentable.
 Instrument[] getInstruments()
          Obtain a reference to all the Instruments that the Instrumentable object wishes to expose.
 int getReadySize()
          Returns the number of available Poolables waiting in the pool.
 int getSize()
          Returns the total number of Poolables created by the pool.
protected  Poolable newPoolable()
          Create a new poolable instance by by calling the newInstance method on the pool's ObjectFactory.
protected  void permanentlyRemovePoolable(Poolable poolable)
          Permanently removes a poolable from the pool's active list and destroys it so that it will not ever be reused.
 void put(Poolable poolable)
          Returns a poolable to the pool and notifies any thread blocking.
protected  void removePoolable(Poolable poolable)
          Called when an object is being removed permanently from the pool.
 void setInstrumentableName(java.lang.String name)
          Sets the name for the Instrumentable.
 int trim()
          Forces the pool to trim, remove, old Poolables from the pool.
 
Methods inherited from class org.apache.avalon.framework.logger.AbstractLogEnabled
enableLogging, getLogger, setupLogger, setupLogger, setupLogger
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface org.apache.avalon.framework.logger.LogEnabled
enableLogging
 

Field Detail

DEFAULT_INSTRUMENTABLE_NAME

public static final java.lang.String DEFAULT_INSTRUMENTABLE_NAME
See Also:
Constant Field Values

INSTRUMENT_SIZE_NAME

public static final java.lang.String INSTRUMENT_SIZE_NAME
See Also:
Constant Field Values

INSTRUMENT_READY_SIZE_NAME

public static final java.lang.String INSTRUMENT_READY_SIZE_NAME
See Also:
Constant Field Values

INSTRUMENT_GETS_NAME

public static final java.lang.String INSTRUMENT_GETS_NAME
See Also:
Constant Field Values

INSTRUMENT_PUTS_NAME

public static final java.lang.String INSTRUMENT_PUTS_NAME
See Also:
Constant Field Values

INSTRUMENT_BLOCKS_NAME

public static final java.lang.String INSTRUMENT_BLOCKS_NAME
See Also:
Constant Field Values

INSTRUMENT_CREATES_NAME

public static final java.lang.String INSTRUMENT_CREATES_NAME
See Also:
Constant Field Values

INSTRUMENT_DECOMMISSIONS_NAME

public static final java.lang.String INSTRUMENT_DECOMMISSIONS_NAME
See Also:
Constant Field Values

m_semaphore

protected final java.lang.Object m_semaphore
Object used to synchronize access to the get and put methods

Constructor Detail

InstrumentedResourceLimitingPool

public InstrumentedResourceLimitingPool(ObjectFactory factory,
                                        int max,
                                        boolean maxStrict,
                                        boolean blocking,
                                        long blockTimeout,
                                        long trimInterval)
Creates a new InstrumentedResourceLimitingPool

Parameters:
factory - The ObjectFactory which will be used to create new Poolables as needed by the pool.
max - Maximum number of Poolables which can be stored in the pool, 0 implies no limit.
maxStrict - true if the pool should never allow more than max Poolable to be created. Will cause an exception to be thrown if more than max Poolables are requested and blocking is false.
blocking - true if the pool should cause a thread calling get() to block when Poolables are not currently available in the pool.
blockTimeout - The maximum amount of time, in milliseconds, that a call to get() will block before an exception is thrown. A value of 0 implies an indefinate wait.
trimInterval - The minimum interval with which old unused poolables will be removed from the pool. A value of 0 will cause the pool to never trim poolables.
Method Detail

get

public Poolable get()
             throws java.lang.Exception
Gets a Poolable from the pool. If there is room in the pool, a new Poolable will be created. Depending on the parameters to the constructor, the method may block or throw an exception if a Poolable is not available on the pool.

Specified by:
get in interface Pool
Returns:
Always returns a Poolable. Contract requires that put must always be called with the Poolable returned.
Throws:
java.lang.Exception - An exception may be thrown as described above or if there is an exception thrown by the ObjectFactory's newInstance() method.

put

public void put(Poolable poolable)
Returns a poolable to the pool and notifies any thread blocking.

Specified by:
put in interface Pool
Parameters:
poolable - Poolable to return to the pool.

dispose

public void dispose()
The dispose operation is called at the end of a components lifecycle. This method will be called after Startable.stop() method (if implemented by component). Components use this method to release and destroy any resources that the Component owns.

Specified by:
dispose in interface Disposable

setInstrumentableName

public void setInstrumentableName(java.lang.String name)
Sets the name for the Instrumentable. The Instrumentable Name is used to uniquely identify the Instrumentable during the configuration of the InstrumentManager and to gain access to an InstrumentableDescriptor through the InstrumentManager. The value should be a string which does not contain spaces or periods.

This value may be set by a parent Instrumentable, or by the InstrumentManager using the value of the 'instrumentable' attribute in the configuration of the component.

Specified by:
setInstrumentableName in interface Instrumentable
Parameters:
name - The name used to identify a Instrumentable.

getInstrumentableName

public java.lang.String getInstrumentableName()
Gets the name of the Instrumentable.

Specified by:
getInstrumentableName in interface Instrumentable
Returns:
The name used to identify a Instrumentable.

getInstruments

public Instrument[] getInstruments()
Obtain a reference to all the Instruments that the Instrumentable object wishes to expose. All sampling is done directly through the Instruments as opposed to the Instrumentable interface.

Specified by:
getInstruments in interface Instrumentable
Returns:
An array of the Instruments available for profiling. Should never be null. If there are no Instruments, then EMPTY_INSTRUMENT_ARRAY can be returned. This should never be the case though unless there are child Instrumentables with Instruments.

getChildInstrumentables

public Instrumentable[] getChildInstrumentables()
Any Object which implements Instrumentable can also make use of other Instrumentable child objects. This method is used to tell the InstrumentManager about them.

Specified by:
getChildInstrumentables in interface Instrumentable
Returns:
An array of child Instrumentables. This method should never return null. If there are no child Instrumentables, then EMPTY_INSTRUMENTABLE_ARRAY can be returned.

permanentlyRemovePoolable

protected void permanentlyRemovePoolable(Poolable poolable)
Permanently removes a poolable from the pool's active list and destroys it so that it will not ever be reused.

This method is only called by threads that have m_semaphore locked.


getSize

public int getSize()
Returns the total number of Poolables created by the pool. Includes active and ready.

Returns:
The total size.

getReadySize

public int getReadySize()
Returns the number of available Poolables waiting in the pool.

Returns:
The ready size.

newPoolable

protected Poolable newPoolable()
                        throws java.lang.Exception
Create a new poolable instance by by calling the newInstance method on the pool's ObjectFactory.

This is the method to override when you need to enforce creational policies.

This method is only called by threads that have m_semaphore locked.

Throws:
java.lang.Exception

removePoolable

protected void removePoolable(Poolable poolable)
Called when an object is being removed permanently from the pool. This is the method to override when you need to enforce destructional policies.

This method is only called by threads that have m_semaphore locked.

Parameters:
poolable - Poolable to be completely removed from the pool.

trim

public int trim()
Forces the pool to trim, remove, old Poolables from the pool. If the Pool was created with a non-zero value for trimInterval, then this method will be called at that interval when get() is called. If get() is not called for long periods of time then if may be necessary to call this method manually.

Trimming is done by maintaining two lists of objects. The first is a ready list of new poolables. The second is a list of old poolables. Each time trim() is called, the contents of the old list are removed from the pool. Then the contents of the new list is moved into the old list.

Each time get() is called on the pool, the new list is checked first, then the old list is checked, finally a new poolable may be created if both lists are empty. Then whenever put() is called, the poolables are always returned to the new list. In this way, the need for maining time stamps for each poolable can be avoided while at the same time avoiding unnecessary removal and creation on poolables.

This works out to a poolable having a maximum idle time of two calls to trim() or twice the value of trimInterval.

NOTE - The trimming feature does not harm performance because pools with high load will not have old poolables to be trimmed, and the benefits to system resources from not keeping around unused poolables makes up for any hit.

Returns:
the number of Poolables that were trimmed.


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