org.wandora.topicmap.database

Class WeakTopicIndex

java.lang.Object

org.wandora.topicmap.database.WeakTopicIndex

All Implemented Interfaces:

java.lang.Runnable

public class WeakTopicIndex
extends java.lang.Object
implements java.lang.Runnable

WeakTopicIndex keeps an index of every topic and association created with it. Database topic map creates all topics and associations with it instead of creating them directly. The index is done with WeakReferences so that Java garbage collector can collect the indexed topics at any time if there are no strong references to them elsewhere. With this kind of index, it is possible to make sure that at any time there is at most one topic object for each individual topic in the database but at the same time allow garbage collector to clean topics that are not referenced anywhere else than the index.

WeakTopicIndex needs to have a cleaner thread running that cleans the WeakReferences when garbage collector has collected the referred objects.

In addition, a strong reference to 2000 most used topics is maintained. This acts as a sort of cache to keep frequently accessed topics in memory even if strong references are not kept outside the index. This cache is maintained with the WeakTopicIndex.CacheList class.

Author:

olli

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	WeakTopicIndex.CacheList<E> Cache list is a list of objects where the most used objects are at the top of the list and least used objects are at the bottom.

Field Summary

Fields

Modifier and Type	Field and Description
private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseAssociation>>	associationIDIndex
private java.util.HashMap<java.lang.ref.WeakReference<DatabaseAssociation>,java.lang.String>	associationInvIDIndex
private java.lang.ref.ReferenceQueue<DatabaseAssociation>	associationRefQueue
private boolean	running
private java.lang.Thread	thread
private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseTopic>>	topicBNIndex
private WeakTopicIndex.CacheList<DatabaseTopic>	topicCache A CacheList that keeps (strong) references to topics so they do not get carbage collected.
private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseTopic>>	topicIDIndex
private java.util.HashMap<java.lang.ref.WeakReference<DatabaseTopic>,java.lang.String>	topicInvBNIndex
private java.util.HashMap<java.lang.ref.WeakReference<DatabaseTopic>,java.lang.String>	topicInvIDIndex
private MultiHashMap<java.lang.ref.WeakReference<DatabaseTopic>,Locator>	topicInvSIIndex
private java.lang.ref.ReferenceQueue<DatabaseTopic>	topicRefQueue
private java.util.HashMap<Locator,java.lang.ref.WeakReference<DatabaseTopic>>	topicSIIndex
private boolean	useRefQueue if references queues are being used, that is if we are keeping track of topics/associations that have been garbage collected

Constructor Summary

Constructors

Constructor and Description
WeakTopicIndex() Creates a new instance of WeakTopicIndex

Method Summary

Modifier and Type	Method and Description
void	addNullBN(java.lang.String bn)
void	addNullSI(Locator si)
void	clearTopicCache() Clears the topic cache allowing any topic that isn't (strongly) referenced elsewhere to be gargbage collected and removed from the index.
boolean	containsKeyWithBN(java.lang.String bn)
boolean	containsKeyWithID(java.lang.String id)
boolean	containsKeyWithSI(Locator si)
DatabaseAssociation	createAssociation(java.lang.String id, DatabaseTopicMap tm)
DatabaseTopic	createTopic(java.lang.String id, DatabaseTopicMap tm) Constructs a DatabaseTopic with the given ID.
void	destroy()
DatabaseAssociation	getAssociation(java.lang.String id, DatabaseTopicMap tm)
DatabaseTopic	getTopicWithBN(java.lang.String bn)
DatabaseTopic	getTopicWithID(java.lang.String id)
DatabaseTopic	getTopicWithSI(Locator si)
boolean	isFullIndex() If the indexes are complete.
boolean	isNullBN(java.lang.String bn)
boolean	isNullSI(Locator si)
DatabaseAssociation	newAssociation(DatabaseTopic type, DatabaseTopicMap tm)
DatabaseTopic	newTopic(DatabaseTopicMap tm) Creates a new topic and adds it to the index.
DatabaseTopic	newTopic(java.lang.String id, DatabaseTopicMap tm) Creates a new topic and adds it to the index.
void	printDebugInfo()
private void	removeAssociationKey(java.lang.ref.Reference<? extends DatabaseAssociation> ref)
private void	removeTopicKey(java.lang.ref.Reference<? extends DatabaseTopic> ref) Removes entries that refer to the given WeakReferenc from topic indexes.
void	run()
void	startCleanerThread() Restarts the thread that is cleaning indexes of topics/associations that have been garbage collected.
void	stopCleanerThread() Stops the thread that is cleaning indexes of topics/associations that have been garbage collected.
private DatabaseTopic	topicAccessed(DatabaseTopic topic) Accesses a topic moving it up or adding it to the CacheList.
void	topicBNChanged(Topic t, java.lang.String old)
void	topicRemoved(Topic t)
void	topicSIChanged(DatabaseTopic t, Locator deleted, Locator added)

Methods inherited from class java.lang.Object

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

Field Detail

running

private boolean running

thread

private java.lang.Thread thread

topicRefQueue

private java.lang.ref.ReferenceQueue<DatabaseTopic> topicRefQueue

topicIDIndex

private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseTopic>> topicIDIndex

topicSIIndex

private java.util.HashMap<Locator,java.lang.ref.WeakReference<DatabaseTopic>> topicSIIndex

topicBNIndex

private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseTopic>> topicBNIndex

topicInvIDIndex

private java.util.HashMap<java.lang.ref.WeakReference<DatabaseTopic>,java.lang.String> topicInvIDIndex

topicInvSIIndex

private MultiHashMap<java.lang.ref.WeakReference<DatabaseTopic>,Locator> topicInvSIIndex

topicInvBNIndex

private java.util.HashMap<java.lang.ref.WeakReference<DatabaseTopic>,java.lang.String> topicInvBNIndex

associationRefQueue

private java.lang.ref.ReferenceQueue<DatabaseAssociation> associationRefQueue

associationIDIndex

private java.util.HashMap<java.lang.String,java.lang.ref.WeakReference<DatabaseAssociation>> associationIDIndex

associationInvIDIndex

private java.util.HashMap<java.lang.ref.WeakReference<DatabaseAssociation>,java.lang.String> associationInvIDIndex

topicCache

private WeakTopicIndex.CacheList<DatabaseTopic> topicCache

A CacheList that keeps (strong) references to topics so they do not get carbage collected. This keeps (roughly speaking) the 2000 most used topics in memory at all times and allows them to be retrieved quickly from the weak indexes. Without keeping strong references to them they would be garbage collected and the indexes would be of little use.

useRefQueue

private boolean useRefQueue

if references queues are being used, that is if we are keeping track of topics/associations that have been garbage collected

Constructor Detail

WeakTopicIndex

public WeakTopicIndex()

Creates a new instance of WeakTopicIndex

Method Detail

clearTopicCache

public void clearTopicCache()

Clears the topic cache allowing any topic that isn't (strongly) referenced elsewhere to be gargbage collected and removed from the index. Note that this does not actually clear the index.

stopCleanerThread

public void stopCleanerThread()

Stops the thread that is cleaning indexes of topics/associations that have been garbage collected.

startCleanerThread

public void startCleanerThread()

Restarts the thread that is cleaning indexes of topics/associations that have been garbage collected.

isFullIndex

public boolean isFullIndex()

If the indexes are complete. Note that even though they are complete some of the indexed topics/associations may have been garbage collected and index only contains information that something has been in there. This makes it possible to determine if some topic exists but isn't anymore in the index or if it doesn't exist.

destroy

public void destroy()

newTopic

public DatabaseTopic newTopic(java.lang.String id,
                              DatabaseTopicMap tm)
                       throws TopicMapException

Creates a new topic and adds it to the index.

Throws:

TopicMapException

newTopic

public DatabaseTopic newTopic(DatabaseTopicMap tm)
                       throws TopicMapException

Creates a new topic and adds it to the index.

Throws:

TopicMapException

topicAccessed

private DatabaseTopic topicAccessed(DatabaseTopic topic)

Accesses a topic moving it up or adding it to the CacheList.

createTopic

public DatabaseTopic createTopic(java.lang.String id,
                                 DatabaseTopicMap tm)

Constructs a DatabaseTopic with the given ID.

getTopicWithID

public DatabaseTopic getTopicWithID(java.lang.String id)

containsKeyWithID

public boolean containsKeyWithID(java.lang.String id)

containsKeyWithSI

public boolean containsKeyWithSI(Locator si)

containsKeyWithBN

public boolean containsKeyWithBN(java.lang.String bn)

isNullSI

public boolean isNullSI(Locator si)

isNullBN

public boolean isNullBN(java.lang.String bn)

getTopicWithSI

public DatabaseTopic getTopicWithSI(Locator si)

getTopicWithBN

public DatabaseTopic getTopicWithBN(java.lang.String bn)

topicSIChanged

public void topicSIChanged(DatabaseTopic t,
                           Locator deleted,
                           Locator added)

addNullSI

public void addNullSI(Locator si)

addNullBN

public void addNullBN(java.lang.String bn)

topicBNChanged

public void topicBNChanged(Topic t,
                           java.lang.String old)
                    throws TopicMapException

Throws:

TopicMapException

topicRemoved

public void topicRemoved(Topic t)
                  throws TopicMapException

Throws:

TopicMapException

newAssociation

public DatabaseAssociation newAssociation(DatabaseTopic type,
                                          DatabaseTopicMap tm)
                                   throws TopicMapException

Throws:

TopicMapException

createAssociation

public DatabaseAssociation createAssociation(java.lang.String id,
                                             DatabaseTopicMap tm)

getAssociation

public DatabaseAssociation getAssociation(java.lang.String id,
                                          DatabaseTopicMap tm)

removeTopicKey

private void removeTopicKey(java.lang.ref.Reference<? extends DatabaseTopic> ref)

Removes entries that refer to the given WeakReferenc from topic indexes. This is used after a topic has been gargbage collected and it is not needed anymore in the indexes.

removeAssociationKey

private void removeAssociationKey(java.lang.ref.Reference<? extends DatabaseAssociation> ref)

printDebugInfo

public void printDebugInfo()

run

public void run()

Specified by:

run in interface java.lang.Runnable