org.das2.qds

Class ReferenceCache

java.lang.Object

org.das2.qds.ReferenceCache

public class ReferenceCache
extends java.lang.Object

Provide a cache of datasets that are in memory, so that the same data is not loaded twice. This first implementation uses WeakReferences, so that this cache need not be emptied, but we will avoid the situation where the same data is loaded twice.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ReferenceCache.ReferenceCacheEntry Keep track of the status of a load.
static class	ReferenceCache.ReferenceCacheEntryStatus

Method Summary

Modifier and Type	Method and Description
QDataSet	getDataSet(java.lang.String uri) Query to see if the dataset exists in the cache.
ReferenceCache.ReferenceCacheEntry	getDataSetOrLock(java.lang.String uri, ProgressMonitor monitor) Get a ReferenceCacheEntry for the URI, which will indicate the thread which has been designated as the load thread.
static ReferenceCache	getInstance() get the single instance of the ReferenceCache
void	park(ReferenceCache.ReferenceCacheEntry ent, ProgressMonitor monitor) park this thread until the other guy has finished loading.
void	printStatus() display the status of all the entries.
void	putDataSet(java.lang.String uri, QDataSet ds) put the dataset into the ReferenceCache.
void	reset() explicitly remove entries from the cache.
void	tidy() remove all the entries that have been garbage collected.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static ReferenceCache getInstance()

get the single instance of the ReferenceCache

Returns:

getDataSet

public QDataSet getDataSet(java.lang.String uri)

Query to see if the dataset exists in the cache. Null is returned if it is not, or a QDataSet is returned if it is.

Parameters:

uri - the URI that can be resolved into a dataset.

Returns:

the dataset or null

getDataSetOrLock

public ReferenceCache.ReferenceCacheEntry getDataSetOrLock(java.lang.String uri,
                                                           ProgressMonitor monitor)

Get a ReferenceCacheEntry for the URI, which will indicate the thread which has been designated as the load thread.

rcent= ReferenceCache.getInstance().getDataSetOrLock( this.tsb.getURI(), mon);
if ( !rcent.shouldILoad( Thread.currentThread() ) ) { 
   QDataSet result= rcent.park( mon );
}

Be sure to use try/finally when using this cache!

Parameters:

uri - the URI to load.

monitor - to monitor the load.

Returns:

the ReferenceCacheEntry

park

public void park(ReferenceCache.ReferenceCacheEntry ent,
                 ProgressMonitor monitor)

park this thread until the other guy has finished loading.

Parameters:

ent -

monitor - the monitor of the load.

putDataSet

public void putDataSet(java.lang.String uri,
                       QDataSet ds)

put the dataset into the ReferenceCache. If it is mutable, then a copy is made.

Parameters:

uri -

ds -

reset

public void reset()

explicitly remove entries from the cache.

tidy

public void tidy()

remove all the entries that have been garbage collected.

printStatus

public void printStatus()

display the status of all the entries.