com.wutka.util
Class ResourcePool

java.lang.Object
  |
  +--com.wutka.util.ResourcePool

public class ResourcePool

extends java.lang.Object

ResourcePool holds a common set of resources that are given out in first-in-first-out order. The pool assumes that all resources are equally weighted. Since some resource pools may need to allocate additional resources when no more are available, the getOverFlowResource method can be overridden to create new ones.

When the resource is allocated, the requesting thread can associate an object with the allocated resource. One way to make use of this feature is to store the name of the method that is requesting the resource. When debugging code, you may want to look at the allocated resources and what methods have allocated them. Someties you can find methods that aren't releasing resources after allocating them.

If you allocate resources within a try block, you should release them in the finally section of the block. That way, the resource is released no matter what exception is thrown.

Field Summary

protected java.util.Vector	availableResources The resources that are currently free
protected java.util.Vector	usedResourceInfo User-defined info about a resource that has been allocated
protected java.util.Vector	usedResources Resources that have been allocated out of the pool

Constructor Summary

ResourcePool()
Creates a new resource pool

Method Summary

void	addResource(java.lang.Object resource) Adds another resource to the pool
protected void	doNotify() Performs a notifyAll (which requires a synchronized method)
protected void	doWait(long timeout) Performs a wait for a specified number of milliseconds.
protected void	doWakeup()
java.util.Vector	getAvailableResources() Return a copy of the resources in the free list
protected java.lang.Object	getOverflowResource() Allocates a resource when the pool is empty.
java.lang.Object	getResource() Requests a resource from the pool, waiting forever if one is not available.
java.lang.Object	getResource(long timeout) Requests a resource from the pool, waiting forever if one is not available.
java.lang.Object	getResource(java.lang.Object allocationInfo) Requests a resource from the pool, waiting forever if one is not available.
java.lang.Object	getResource(java.lang.Object allocationInfo, long timeout) Requests a resource from the pool, waiting forever if one is not available.
protected java.lang.Object	getResourceFromList(java.lang.Object allocationInfo) Grabs a resource from the free list and moves it to the used list.
java.util.Vector	getUsedResourceInfo() Return a copy of the associated info for the used resources
java.util.Vector	getUsedResources() Return a copy of the resources in the used list
void	releaseResource(java.lang.Object resource) Releases a resource back to the pool of available resources
void	removeResource(java.lang.Object resource) Removes a resource from the pool

Methods inherited from class java.lang.Object

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

Field Detail

availableResources

protected java.util.Vector availableResources

The resources that are currently free

usedResources

protected java.util.Vector usedResources

Resources that have been allocated out of the pool

usedResourceInfo

protected java.util.Vector usedResourceInfo

User-defined info about a resource that has been allocated

Constructor Detail

ResourcePool

public ResourcePool()

Creates a new resource pool

Method Detail

addResource

public void addResource(java.lang.Object resource)

Adds another resource to the pool

Parameters:

resource - The resource being added

removeResource

public void removeResource(java.lang.Object resource)

Removes a resource from the pool

Parameters:

resource - The resource to be removed

getOverflowResource

protected java.lang.Object getOverflowResource()

Allocates a resource when the pool is empty. By default, this method returns null, indicating that the requesting thread must wait. This allows a thread pool to expand when necessary, allowing for spikes in activity.

Returns:

A new resource, or null to force the requester to wait

getResource

public java.lang.Object getResource()

Requests a resource from the pool, waiting forever if one is not available. No extra information is associated with the allocated resource.

Returns:

The allocated resource

getResource

public java.lang.Object getResource(java.lang.Object allocationInfo)

Requests a resource from the pool, waiting forever if one is not available.

Parameters:

allocationInfo - A value associated with the allocated resource

Returns:

The allocated resource

getResource

public java.lang.Object getResource(long timeout)

Requests a resource from the pool, waiting forever if one is not available.

Parameters:

timeout - The maximum amount of time (in milliseconds) to wait for the resource

Returns:

The allocated resource

getResourceFromList

protected java.lang.Object getResourceFromList(java.lang.Object allocationInfo)

Grabs a resource from the free list and moves it to the used list. This method is really the core of the resource pool. The rest of the class deals with synchronization around this method.

Parameters:

allocationInfo - The info to be associated with the allocated resource

Returns:

The allocated resource

doWait

protected void doWait(long timeout)

Performs a wait for a specified number of milliseconds.

Parameters:

timeout - The number of milliseconds to wait (wait forever if timeout < 0)

getResource

public java.lang.Object getResource(java.lang.Object allocationInfo,
                                    long timeout)

Requests a resource from the pool, waiting forever if one is not available.

Parameters:

allocationInfo - A value associated with the allocated resource

timeout - The maximum amount of time (in milliseconds) to wait for the resource

Returns:

The allocated resource

releaseResource

public void releaseResource(java.lang.Object resource)

Releases a resource back to the pool of available resources

Parameters:

resource - The resource to be returned to the pool

doNotify

protected void doNotify()

Performs a notifyAll (which requires a synchronized method)

doWakeup

protected void doWakeup()

getAvailableResources

public java.util.Vector getAvailableResources()

Return a copy of the resources in the free list

Returns:

The resources in the free list

getUsedResources

public java.util.Vector getUsedResources()

Return a copy of the resources in the used list

Returns:

The resources in the used list

getUsedResourceInfo

public java.util.Vector getUsedResourceInfo()

Return a copy of the associated info for the used resources

Returns:

The info associated with the allocated resources