org.forgerock.openam.utils

Class PerThreadCache<T,E extends Exception>

java.lang.Object

org.forgerock.openam.utils.PerThreadCache<T,E>

Type Parameters:

T - The cache entry type.

E - The exception type.

public abstract class PerThreadCache<T,E extends Exception>
extends Object

Provides caching of some expensive objects in a per-thread LRU cache for performance. Note: this cache does not use real ThreadLocal storage because of issues with cleanup and garbage collection. Instead we use an internal map keyed by thread id to lookup a per-thread instance of the underlying resource, creating one if not present for this thread. The map also acts as a LRU cache, ensuring a maximum size limit is obeyed by evicting the least recently used (LRU) entry whenever it grows beyond capacity.

Since:

12.0.0

Constructor Summary

Constructors

Constructor and Description
PerThreadCache(int maxSize) Initialises the thread-local cache with the given maximum size (i.e., number of threads).

Method Summary

Modifier and Type	Method and Description
T	getInstanceForCurrentThread() Fetches an instance of the resource from the cache for the current thread.
protected abstract T	initialValue() Method will be called to initialise a fresh instance of the underlying resource when one is not found in the cache.

Methods inherited from class java.lang.Object

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

Constructor Detail

PerThreadCache

public PerThreadCache(int maxSize)

Initialises the thread-local cache with the given maximum size (i.e., number of threads).

Parameters:

maxSize - the maximum number of instances to cache.

Method Detail

getInstanceForCurrentThread

public final T getInstanceForCurrentThread()
                                    throws E extends Exception

Fetches an instance of the resource from the cache for the current thread. If no instance has been cached for this thread, then calls initialValue() to create one and then adds it to the cache. If this causes the cache to exceed the configured maximum size then the least recently used (LRU) entry will be deleted from the cache to preserve the capacity restriction.

Returns:

a configured instance from the cache. May be null depending on the initialValue() implementation.

Throws:

E - when an error occurs.

E extends Exception

initialValue

protected abstract T initialValue()
                           throws E extends Exception

Method will be called to initialise a fresh instance of the underlying resource when one is not found in the cache. Concrete sub-classes should implement this method as per requirements.

Returns:

a fresh instance of the underlying resource.

Throws:

E - if the resource instance cannot be created.

E extends Exception