com.bigdata.relation.locator
Class AbstractCachingResourceLocator<T extends ILocatableResource>

java.lang.Object
  com.bigdata.relation.locator.AbstractCachingResourceLocator<T>

All Implemented Interfaces:

IResourceLocator<T>

Direct Known Subclasses:

DefaultResourceLocator

public abstract class AbstractCachingResourceLocator<T extends ILocatableResource>
extends Object
implements IResourceLocator<T>

Abstract base class for IResourceLocators with caching. The cache uses WeakReferences so that cache entries will be cleared if the referenced item is cleared.

Version:

$Id: AbstractCachingResourceLocator.java 2265 2009-10-26 12:51:06Z thompsonbry $

Author:

Bryan Thompson

Field Summary

protected static boolean	INFO
protected static org.apache.log4j.Logger	log

Constructor Summary

protected

AbstractCachingResourceLocator(int capacity, long timeout)

Method Summary

int	capacity() The cache capacity.
protected boolean	clear(String namespace, long timestamp) Clears any resource having the same namespace and timestamp from the cache.
protected T	get(String namespace, long timestamp) Looks up the resource in the cache (thread-safe since the underlying cache is thread-safe).
protected void	put(T resource) Places the resource in the cache.

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.bigdata.relation.locator.IResourceLocator

locate

Field Detail

log

protected static final org.apache.log4j.Logger log

INFO

protected static final boolean INFO

Constructor Detail

AbstractCachingResourceLocator

protected AbstractCachingResourceLocator(int capacity,
                                         long timeout)

Parameters:

capacity - The cache capacity.

timeout - The timeout in milliseconds for stale entries.

Method Detail

capacity

public final int capacity()

The cache capacity.

get

protected T get(String namespace,
                long timestamp)

Looks up the resource in the cache (thread-safe since the underlying cache is thread-safe).

Parameters:

namespace -

timestamp -

Returns:

The relation -or- null iff it is not in the cache.

put

protected void put(T resource)

Places the resource in the cache.

Note: The underlying cache is thread-safe. However, when adding an entry to the cache the caller MUST be synchronized on the named resource, use get(String, long) to determine that there is no such entry in the cache, and then put(ILocatableResource) the entry.

Note: Read committed views are allowed into the cache.

For a Journal, this depends on Journal#getIndex(name,timestamp) returning a ReadCommittedView for an index so that the view does in fact have read-committed semantics.

For a federation, read-committed semantics are achieved by the IClientIndex implementations since they always make standoff requests to one (or more) data services. Those requests allow the data service to resolve the then most recent view for the index for each request.

Parameters:

resource - The resource.

clear

protected boolean clear(String namespace,
                        long timestamp)

Clears any resource having the same namespace and timestamp from the cache.

Note: The caller MUST be synchronized on the named resource.

Returns:

true iff there was an entry in the cache for the same resource namespace and timestamp, in which case it was cleared from the cache.