org.apache.jcs.auxiliary.disk

Class AbstractDiskCache

java.lang.Object

org.apache.jcs.auxiliary.AbstractAuxiliaryCache

org.apache.jcs.auxiliary.AbstractAuxiliaryCacheEventLogging

org.apache.jcs.auxiliary.disk.AbstractDiskCache

All Implemented Interfaces:

java.io.Serializable, AuxiliaryCache, ICache, ICacheType

Direct Known Subclasses:

BlockDiskCache, IndexedDiskCache, JDBCDiskCache

public abstract class AbstractDiskCache
extends AbstractAuxiliaryCacheEventLogging
implements AuxiliaryCache, java.io.Serializable

Abstract class providing a base implementation of a disk cache, which can be easily extended to implement a disk cache for a specific persistence mechanism.

When implementing the abstract methods note that while this base class handles most things, it does not acquire or release any locks. Implementations should do so as necessary. This is mainly done to minimize the time spent in critical sections.

Error handling in this class needs to be addressed. Currently if an exception is thrown by the persistence mechanism, this class destroys the event queue. Should it also destroy purgatory? Should it dispose itself?

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	alive Indicates whether the cache is 'alive': initialized, but not yet disposed.
protected ICacheEventQueue	cacheEventQueue The CacheEventQueue where changes will be queued for asynchronous updating of the persistent storage.
protected java.lang.String	cacheName Every cache will have a name, subclasses must set this when they are initialized.
protected java.util.Map	purgatory Map where elements are stored between being added to this cache and actually spooled to disk.
protected int	purgHits DEBUG: Keeps a count of the number of purgatory hits for debug messages

Fields inherited from class org.apache.jcs.auxiliary.AbstractAuxiliaryCache

cacheEventLogger, elementSerializer, keyMatcher

Fields inherited from interface org.apache.jcs.engine.behavior.ICacheType

CACHE_HUB, DISK_CACHE, LATERAL_CACHE, REMOTE_CACHE

Constructor Summary

Constructors

Constructor and Description
AbstractDiskCache(IDiskCacheAttributes attr) Construct the abstract disk cache, create event queues and purgatory.

Method Summary

Methods

Modifier and Type	Method and Description
void	dispose() Adds a dispose request to the disk cache.
protected void	doDispose() Dispose of the persistent store.
protected ICacheElement	doGet(java.io.Serializable key) Get a value from the persistent store.
protected java.util.Map	doGetMatching(java.lang.String pattern) Get a value from the persistent store.
protected boolean	doRemove(java.io.Serializable key) Remove an object from the persistent store if found.
protected void	doRemoveAll() Remove all objects from the persistent store.
protected void	doUpdate(ICacheElement cacheElement) Add a cache element to the persistent store.
ICacheElement	get(java.io.Serializable key) Check to see if the item is in purgatory.
java.lang.String	getCacheName() Returns the cache name.
int	getCacheType() Returns the cache type.
protected abstract java.lang.String	getDiskLocation() This is used by the event logging.
java.lang.String	getEventLoggingExtraInfo() Gets the extra info for the event log.
abstract java.util.Set	getGroupKeys(java.lang.String groupName) The keys in a group.
java.util.Map	getMatching(java.lang.String pattern) Gets items from the cache matching the given pattern.
abstract int	getSize() Size cannot be determined without knowledge of the cache implementation, so subclasses will need to implement this method.
IStats	getStatistics() Returns semi-structured data.
java.lang.String	getStats() Gets basic stats for the abstract disk cache.
int	getStatus() Returns the cache status.
java.util.Map	processGetMultiple(java.util.Set keys) Gets multiple items from the cache based on the given set of keys.
boolean	remove(java.io.Serializable key) Removes are not queued.
void	removeAll() Removes all from the region.
void	update(ICacheElement cacheElement) Adds the provided element to the cache.

Methods inherited from class org.apache.jcs.auxiliary.AbstractAuxiliaryCacheEventLogging

disposeWithEventLogging, getMatchingWithEventLogging, getMultiple, getMultipleWithEventLogging, getWithEventLogging, processDispose, processGet, processGetMatching, processRemove, processRemoveAll, processUpdate, removeAllWithEventLogging, removeWithEventLogging, updateWithEventLogging

Methods inherited from class org.apache.jcs.auxiliary.AbstractAuxiliaryCache

createICacheEvent, createICacheEvent, getCacheEventLogger, getElementSerializer, getKeyMatcher, logApplicationEvent, logError, logICacheEvent, setCacheEventLogger, setElementSerializer, setKeyMatcher

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.jcs.auxiliary.AuxiliaryCache

getAuxiliaryCacheAttributes, setCacheEventLogger, setElementSerializer

Methods inherited from interface org.apache.jcs.engine.behavior.ICache

getMultiple, setKeyMatcher

Field Detail

purgatory

protected java.util.Map purgatory

Map where elements are stored between being added to this cache and actually spooled to disk. This allows puts to the disk cache to return quickly, and the more expensive operation of serializing the elements to persistent storage queued for later.

If the elements are pulled into the memory cache while the are still in purgatory, writing to disk can be canceled.

cacheEventQueue

protected ICacheEventQueue cacheEventQueue

The CacheEventQueue where changes will be queued for asynchronous updating of the persistent storage.

alive

protected boolean alive

Indicates whether the cache is 'alive': initialized, but not yet disposed.

cacheName

protected java.lang.String cacheName

Every cache will have a name, subclasses must set this when they are initialized.

purgHits

protected int purgHits

DEBUG: Keeps a count of the number of purgatory hits for debug messages

Constructor Detail

AbstractDiskCache

public AbstractDiskCache(IDiskCacheAttributes attr)

Construct the abstract disk cache, create event queues and purgatory.

Parameters:

attr -

Method Detail

update

public final void update(ICacheElement cacheElement)
                  throws java.io.IOException

Adds the provided element to the cache. Element will be added to purgatory, and then queued for later writing to the serialized storage mechanism.

An update results in a put event being created. The put event will call the handlePut method defined here. The handlePut method calls the implemented doPut on the child.

Specified by:

update in interface ICache

Overrides:

update in class AbstractAuxiliaryCacheEventLogging

Parameters:

cacheElement -

Throws:

java.io.IOException

See Also:

ICache.update(org.apache.jcs.engine.behavior.ICacheElement)

get

public final ICacheElement get(java.io.Serializable key)

Check to see if the item is in purgatory. If so, return it. If not, check to see if we have it on disk.

Specified by:

get in interface ICache

Overrides:

get in class AbstractAuxiliaryCacheEventLogging

Parameters:

key -

Returns:

ICacheElement or null

See Also:

ICache.get(java.io.Serializable)

getMatching

public java.util.Map getMatching(java.lang.String pattern)
                          throws java.io.IOException

Gets items from the cache matching the given pattern. Items from memory will replace those from remote sources.

This only works with string keys. It's too expensive to do a toString on every key.

Auxiliaries will do their best to handle simple expressions. For instance, the JDBC disk cache will convert * to % and . to _

Specified by:

getMatching in interface ICache

Overrides:

getMatching in class AbstractAuxiliaryCacheEventLogging

Parameters:

pattern -

Returns:

a map of Serializable key to ICacheElement element, or an empty map if there is no data matching the pattern.

Throws:

java.io.IOException

processGetMultiple

public java.util.Map processGetMultiple(java.util.Set keys)

Gets multiple items from the cache based on the given set of keys.

Specified by:

processGetMultiple in class AbstractAuxiliaryCacheEventLogging

Parameters:

keys -

Returns:

a map of Serializable key to ICacheElement element, or an empty map if there is no data in cache for any of these keys

getGroupKeys

public abstract java.util.Set getGroupKeys(java.lang.String groupName)

The keys in a group.

(non-Javadoc)

Specified by:

getGroupKeys in interface AuxiliaryCache

Returns:

a set of group keys

See Also:

AuxiliaryCache.getGroupKeys(java.lang.String)

remove

public final boolean remove(java.io.Serializable key)
                     throws java.io.IOException

Removes are not queued. A call to remove is immediate.

Specified by:

remove in interface ICache

Overrides:

remove in class AbstractAuxiliaryCacheEventLogging

Parameters:

key -

Returns:

whether the item was present to be removed.

Throws:

java.io.IOException

See Also:

ICache.remove(java.io.Serializable)

removeAll

public final void removeAll()
                     throws java.io.IOException

Description copied from class: AbstractAuxiliaryCacheEventLogging

Removes all from the region. Wraps the removeAll in event logs.

Specified by:

removeAll in interface ICache

Overrides:

removeAll in class AbstractAuxiliaryCacheEventLogging

Throws:

java.io.IOException

See Also:

ICache.removeAll()

dispose

public final void dispose()
                   throws java.io.IOException

Adds a dispose request to the disk cache.

Disposal proceeds in several steps.

1. Prior to this call the Composite cache dumped the memory into the disk cache. If it is large then we need to wait for the event queue to finish.
2. Wait until the event queue is empty of until the configured ShutdownSpoolTimeLimit is reached.
3. Call doDispose on the concrete impl.

Specified by:

dispose in interface ICache

Overrides:

dispose in class AbstractAuxiliaryCacheEventLogging

Throws:

java.io.IOException

getCacheName

public java.lang.String getCacheName()

Description copied from interface: ICache

Returns the cache name.

Specified by:

getCacheName in interface ICache

Returns:

the region name.

See Also:

ICache.getCacheName()

getStats

public java.lang.String getStats()

Gets basic stats for the abstract disk cache.

Specified by:

getStats in interface ICache

Returns:

String

getStatistics

public IStats getStatistics()

Returns semi-structured data.

Specified by:

getStatistics in interface AuxiliaryCache

Returns:

the historical and statistical data for a region's auxiliary cache.

See Also:

AuxiliaryCache.getStatistics()

getStatus

public int getStatus()

Description copied from interface: ICache

Returns the cache status.

Specified by:

getStatus in interface ICache

Returns:

the status -- alive or disposed from CacheConstants

See Also:

ICache.getStatus()

getSize

public abstract int getSize()

Size cannot be determined without knowledge of the cache implementation, so subclasses will need to implement this method.

Specified by:

getSize in interface ICache

Returns:

the number of items.

See Also:

ICache.getSize()

getCacheType

public int getCacheType()

Description copied from interface: ICacheType

Returns the cache type.

Specified by:

getCacheType in interface ICacheType

Returns:

Always returns DISK_CACHE since subclasses should all be of that type.

See Also:

ICacheType.getCacheType()

doGet

protected final ICacheElement doGet(java.io.Serializable key)
                             throws java.io.IOException

Get a value from the persistent store.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Parameters:

key - Key to locate value for.

Returns:

An object matching key, or null.

Throws:

java.io.IOException

doGetMatching

protected final java.util.Map doGetMatching(java.lang.String pattern)
                                     throws java.io.IOException

Get a value from the persistent store.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Parameters:

pattern - Used to match keys.

Returns:

A map of matches..

Throws:

java.io.IOException

doUpdate

protected final void doUpdate(ICacheElement cacheElement)
                       throws java.io.IOException

Add a cache element to the persistent store.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Parameters:

cacheElement -

Throws:

java.io.IOException

doRemove

protected final boolean doRemove(java.io.Serializable key)
                          throws java.io.IOException

Remove an object from the persistent store if found.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Parameters:

key - Key of object to remove.

Returns:

whether or no the item was present when removed

Throws:

java.io.IOException

doRemoveAll

protected final void doRemoveAll()
                          throws java.io.IOException

Remove all objects from the persistent store.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Throws:

java.io.IOException

doDispose

protected final void doDispose()
                        throws java.io.IOException

Dispose of the persistent store. Note that disposal of purgatory and setting alive to false does NOT need to be done by this method.

Before the event logging layer, the subclasses implemented the do* methods. Now the do* methods call the *EventLogging method on the super. The *WithEventLogging methods call the abstract process* methods. The children implement the process methods.

Throws:

java.io.IOException

getEventLoggingExtraInfo

public java.lang.String getEventLoggingExtraInfo()

Gets the extra info for the event log.

Specified by:

getEventLoggingExtraInfo in class AbstractAuxiliaryCache

Returns:

disk location

getDiskLocation

protected abstract java.lang.String getDiskLocation()

This is used by the event logging.

Returns:

the location of the disk, either path or ip.