net.sf.ehcache.constructs.blocking
Class BlockingCache

java.lang.Object
  net.sf.ehcache.constructs.blocking.BlockingCache

All Implemented Interfaces:

java.lang.Cloneable, Ehcache

Direct Known Subclasses:

SelfPopulatingCache

public class BlockingCache
extends java.lang.Object
implements Ehcache

A blocking decorator for an Ehcache, backed by a Ehcache.

It allows concurrent read access to elements already in the cache. If the element is null, other reads will block until an element with the same key is put into the cache.

This is useful for constructing read-through or self-populating caches.

This implementation uses the Mutex class from Doug Lea's concurrency package. If you wish to use this class, you will need the concurrent package in your class path.

It features:

• Excellent liveness.
• Fine-grained locking on each element, rather than the cache as a whole.
• Scalability to a large number of threads.

This class has been updated to use Lock striping. The Mutex implementation gives scalability but creates many Mutex objects of 24 bytes each. Lock striping limits their number to 100.

A version of this class is planned which will dynamically use JDK5's concurrency package, which is based on Doug Lea's, so as to avoid a dependency on his package for JDK5 systems. This will not be implemented until JDK5 is released on MacOSX and Linux, as JDK5 will be required to compile it, though any version from JDK1.2 up will be able to run the code, falling back to Doug Lea's concurrency package, if the JDK5 package is not found in the classpath.

The Mutex class does not appear in the JDK5 concurrency package. Doug Lea has generously offered the following advice:

"You should just be able to use ReentrantLock here. We supply ReentrantLock, but not Mutex because the number of cases where a non-reentrant mutex is preferable is small, and most people are more familiar with reentrant seamantics. If you really need a non-reentrant one, the javadocs for class AbstractQueuedSynchronizer include sample code for them."

-Doug

"Hashtable / synchronizedMap uses the "one big fat lock" approach to guard the mutable state of the map. That works, but is a big concurrency bottleneck, as you've observed. You went to the opposite extreme, one lock per key. That works (as long as you've got sufficient synchronization in the cache itself to protect its own data structures.)

Lock striping is a middle ground, partitioning keys into a fixed number of subsets, like the trick used at large theaters for will-call ticket pickup -- there are separate lines for "A-F, G-M, N-R, and S-Z". This way, there are a fixed number of locks, each guarding (hopefully) 1/Nth of the keys." - Brian Goetz

Further improvements to hashing suggested by Joe Bowbeer.

Version:

$Id: BlockingCache.java 704 2008-07-13 00:17:52Z gregluck $

Author:

Greg Luck

Field Summary

protected Ehcache	cache The backing Cache
static int	LOCK_NUMBER The default number of locks to use.
protected Mutex[]	locks Based on the lock striping concept from Brian Goetz.
protected int	timeoutMillis The amount of time to block a thread before a LockTimeoutException is thrown

Constructor Summary

BlockingCache(Ehcache cache)
Creates a BlockingCache which decorates the supplied cache.

Method Summary

void	bootstrap() Bootstrap command.
long	calculateInMemorySize() Gets the size of the memory store for this cache Warning: This method can be very expensive to run.
void	clearStatistics() Resets statistics counters back to 0.
java.lang.Object	clone() Clones a cache.
void	dispose() Flushes all cache items from memory to auxilliary caches and close the auxilliary caches.
void	evictExpiredElements() Causes all elements stored in the Cache to be synchronously checked for expiry, and if expired, evicted.
void	flush() Flushes all cache items from memory to the disk store, and from the DiskStore to disk.
Element	get(java.lang.Object key) Looks up an entry.
Element	get(java.io.Serializable key) Gets an element from the cache.
java.util.Map	getAllWithLoader(java.util.Collection keys, java.lang.Object loaderArgument) This method is not appropriate to use with BlockingCache.
float	getAverageGetTime() The average get time in ms.
BootstrapCacheLoader	getBootstrapCacheLoader() Accessor for the BootstrapCacheLoader associated with this cache.
protected Ehcache	getCache() Retrieve the EHCache backing cache
CacheConfiguration	getCacheConfiguration() Gets the cache configuration this cache was created with.
RegisteredEventListeners	getCacheEventNotificationService() Use this to access the service in order to register and unregister listeners
CacheExceptionHandler	getCacheExceptionHandler() Sets an ExceptionHandler on the Cache.
CacheLoader	getCacheLoader() Gets the CacheLoader registered in this cache
CacheManager	getCacheManager() Gets the CacheManager managing this cache.
long	getDiskExpiryThreadIntervalSeconds()
int	getDiskStoreSize() Returns the number of elements in the disk store.
java.lang.String	getGuid() The GUID for this cache instance can be used to determine whether two cache instance references are pointing to the same cache.
java.util.List	getKeys() Returns the keys for this cache.
java.util.List	getKeysNoDuplicateCheck() Returns a list of all elements in the cache, whether or not they are expired.
java.util.List	getKeysWithExpiryCheck() Returns a list of all elements in the cache.
protected Mutex	getLockForKey(java.lang.Object key) Gets the Mutex to use for a given key.
int	getMaxElementsInMemory() Gets the maximum number of elements to hold in memory.
int	getMaxElementsOnDisk() Gets the maximum number of elements to hold on Disk.
MemoryStoreEvictionPolicy	getMemoryStoreEvictionPolicy() The policy used to evict elements from the MemoryStore.
long	getMemoryStoreSize() Returns the number of elements in the memory store.
java.lang.String	getName() Returns this cache's name
Element	getQuiet(java.lang.Object key) Gets an element from the cache, without updating Element statistics.
Element	getQuiet(java.io.Serializable key) Gets an element from the cache, without updating Element statistics.
int	getSize() Gets the size of the cache.
Statistics	getStatistics() Gets an immutable Statistics object representing the Cache statistics at the time.
int	getStatisticsAccuracy() Accurately measuring statistics can be expensive.
Status	getStatus() Gets the status attribute of the Cache.
int	getTimeoutMillis() Gets the time to wait to acquire a lock.
long	getTimeToIdleSeconds() Gets timeToIdleSeconds.
long	getTimeToLiveSeconds() Gets timeToLiveSeconds.
Element	getWithLoader(java.lang.Object key, CacheLoader loader, java.lang.Object loaderArgument) This method is not appropriate to use with BlockingCache.
void	initialise() Newly created caches do not have a MemoryStore or a DiskStore.
boolean	isDisabled() Whether this cache is disabled.
boolean	isDiskPersistent()
boolean	isElementInMemory(java.lang.Object key) Whether an Element is stored in the cache in Memory, indicating a very low cost of retrieval.
boolean	isElementInMemory(java.io.Serializable key) Whether an Element is stored in the cache in Memory, indicating a very low cost of retrieval.
boolean	isElementOnDisk(java.lang.Object key) Whether an Element is stored in the cache on Disk, indicating a higher cost of retrieval.
boolean	isElementOnDisk(java.io.Serializable key) Whether an Element is stored in the cache on Disk, indicating a higher cost of retrieval.
boolean	isEternal() Are elements eternal.
boolean	isExpired(Element element) Checks whether this cache element has expired.
boolean	isKeyInCache(java.lang.Object key) An inexpensive check to see if the key exists in the cache.
boolean	isOverflowToDisk() Does the overflow go to disk.
boolean	isValueInCache(java.lang.Object value) An extremely expensive check to see if the value exists in the cache.
java.lang.String	liveness() Synchronized version of getName to test liveness of the object lock.
void	load(java.lang.Object key) This method is not appropriate to use with BlockingCache.
void	loadAll(java.util.Collection keys, java.lang.Object argument) This method is not appropriate to use with BlockingCache.
void	put(Element element) Adds an entry and unlocks it
void	put(Element element, boolean doNotNotifyCacheReplicators) Put an element in the cache.
void	putQuiet(Element element) Put an element in the cache, without updating statistics, or updating listeners.
void	registerCacheExtension(CacheExtension cacheExtension) Register a CacheExtension with the cache.
boolean	remove(java.lang.Object key) Removes an Element from the Cache.
boolean	remove(java.lang.Object key, boolean doNotNotifyCacheReplicators) Removes an Element from the Cache.
boolean	remove(java.io.Serializable key) Removes an Element from the Cache.
boolean	remove(java.io.Serializable key, boolean doNotNotifyCacheReplicators) Removes an Element from the Cache.
void	removeAll() Removes all cached items.
void	removeAll(boolean doNotNotifyCacheReplicators) Removes all cached items.
boolean	removeQuiet(java.lang.Object key) Removes an Element from the Cache, without notifying listeners.
boolean	removeQuiet(java.io.Serializable key) Removes an Element from the Cache, without notifying listeners.
void	setBootstrapCacheLoader(BootstrapCacheLoader bootstrapCacheLoader) Sets the bootstrap cache loader.
void	setCacheExceptionHandler(CacheExceptionHandler cacheExceptionHandler) Sets an ExceptionHandler on the Cache.
void	setCacheLoader(CacheLoader cacheLoader) This method is not appropriate to use with BlockingCache.
void	setCacheManager(CacheManager cacheManager) Sets the CacheManager
void	setDisabled(boolean disabled) Disables or enables this cache.
void	setDiskStorePath(java.lang.String diskStorePath) DiskStore paths can conflict between CacheManager instances.
void	setName(java.lang.String name) Sets the cache name which will name.
void	setStatisticsAccuracy(int statisticsAccuracy) Sets the statistics accuracy.
void	setTimeoutMillis(int timeoutMillis) Sets the time to wait to acquire a lock.
void	unregisterCacheExtension(CacheExtension cacheExtension) Unregister a CacheExtension with the cache.

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.ehcache.Ehcache

toString

Field Detail

LOCK_NUMBER

public static final int LOCK_NUMBER

The default number of locks to use. Must be a power of 2

See Also:

Constant Field Values

locks

protected final Mutex[] locks

Based on the lock striping concept from Brian Goetz. See Java Concurrency in Practice 11.4.3

cache

protected final Ehcache cache

The backing Cache

timeoutMillis

protected int timeoutMillis

The amount of time to block a thread before a LockTimeoutException is thrown

Constructor Detail

BlockingCache

public BlockingCache(Ehcache cache)
              throws CacheException

Creates a BlockingCache which decorates the supplied cache.

Parameters:

cache - a backing ehcache.

Throws:

CacheException

Since:

1.2

Method Detail

getCache

protected Ehcache getCache()

Retrieve the EHCache backing cache

getName

public java.lang.String getName()

Returns this cache's name

Specified by:

getName in interface Ehcache

setName

public void setName(java.lang.String name)

Sets the cache name which will name.

Specified by:

setName in interface Ehcache

Parameters:

name - the name of the cache. Should not be null.

getTimeToIdleSeconds

public long getTimeToIdleSeconds()

Gets timeToIdleSeconds.

Specified by:

getTimeToIdleSeconds in interface Ehcache

getTimeToLiveSeconds

public long getTimeToLiveSeconds()

Gets timeToLiveSeconds.

Specified by:

getTimeToLiveSeconds in interface Ehcache

isEternal

public boolean isEternal()

Are elements eternal.

Specified by:

isEternal in interface Ehcache

isOverflowToDisk

public boolean isOverflowToDisk()

Does the overflow go to disk.

Specified by:

isOverflowToDisk in interface Ehcache

getMaxElementsInMemory

public int getMaxElementsInMemory()

Gets the maximum number of elements to hold in memory.

Specified by:

getMaxElementsInMemory in interface Ehcache

getMaxElementsOnDisk

public int getMaxElementsOnDisk()

Description copied from interface: Ehcache

Gets the maximum number of elements to hold on Disk.

Specified by:

getMaxElementsOnDisk in interface Ehcache

Returns:

the maximum number of elements on Disk, or 0 if unlimited

See Also:

Cache.getMaxElementsOnDisk()

getMemoryStoreEvictionPolicy

public MemoryStoreEvictionPolicy getMemoryStoreEvictionPolicy()

The policy used to evict elements from the MemoryStore. This can be one of:

1. LRU - least recently used
2. LFU - least frequently used
3. FIFO - first in first out, the oldest element by creation time

The default value is LRU

Specified by:

getMemoryStoreEvictionPolicy in interface Ehcache

Since:

1.2

isExpired

public boolean isExpired(Element element)
                  throws java.lang.IllegalStateException,
                         java.lang.NullPointerException

Checks whether this cache element has expired.

The element is expired if:

1. the idle time is non-zero and has elapsed, unless the cache is eternal; or
2. the time to live is non-zero and has elapsed, unless the cache is eternal; or
3. the value of the element is null.

Specified by:

isExpired in interface Ehcache

Parameters:

element - the element to check

Returns:

true if it has expired

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

java.lang.NullPointerException - if the element is null

clone

public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException

Clones a cache. This is only legal if the cache has not been initialized. At that point only primitives have been set and no LruMemoryStore or DiskStore has been created.

A new, empty, RegisteredEventListeners is created on clone.

Specified by:

clone in interface Ehcache

Overrides:

clone in class java.lang.Object

Returns:

an object of type Cache

Throws:

java.lang.CloneNotSupportedException

isDiskPersistent

public boolean isDiskPersistent()

Specified by:

isDiskPersistent in interface Ehcache

Returns:

true if the cache overflows to disk and the disk is persistent between restarts

getDiskExpiryThreadIntervalSeconds

public long getDiskExpiryThreadIntervalSeconds()

Specified by:

getDiskExpiryThreadIntervalSeconds in interface Ehcache

Returns:

the interval between runs of the expiry thread, where it checks the disk store for expired elements. It is not the the timeToLiveSeconds.

getCacheEventNotificationService

public RegisteredEventListeners getCacheEventNotificationService()

Use this to access the service in order to register and unregister listeners

Specified by:

getCacheEventNotificationService in interface Ehcache

Returns:

the RegisteredEventListeners instance for this cache.

isElementInMemory

public boolean isElementInMemory(java.io.Serializable key)

Whether an Element is stored in the cache in Memory, indicating a very low cost of retrieval.

Specified by:

isElementInMemory in interface Ehcache

Returns:

true if an element matching the key is found in memory

isElementInMemory

public boolean isElementInMemory(java.lang.Object key)

Whether an Element is stored in the cache in Memory, indicating a very low cost of retrieval.

Specified by:

isElementInMemory in interface Ehcache

Returns:

true if an element matching the key is found in memory

Since:

1.2

isElementOnDisk

public boolean isElementOnDisk(java.io.Serializable key)

Whether an Element is stored in the cache on Disk, indicating a higher cost of retrieval.

Specified by:

isElementOnDisk in interface Ehcache

Returns:

true if an element matching the key is found in the diskStore

isElementOnDisk

public boolean isElementOnDisk(java.lang.Object key)

Whether an Element is stored in the cache on Disk, indicating a higher cost of retrieval.

Specified by:

isElementOnDisk in interface Ehcache

Returns:

true if an element matching the key is found in the diskStore

Since:

1.2

getGuid

public java.lang.String getGuid()

The GUID for this cache instance can be used to determine whether two cache instance references are pointing to the same cache.

Specified by:

getGuid in interface Ehcache

Returns:

the globally unique identifier for this cache instance. This is guaranteed to be unique.

Since:

1.2

getCacheManager

public CacheManager getCacheManager()

Gets the CacheManager managing this cache. For a newly created cache this will be null until it has been added to a CacheManager.

Specified by:

getCacheManager in interface Ehcache

Returns:

the manager or null if there is none

clearStatistics

public void clearStatistics()

Resets statistics counters back to 0.

Specified by:

clearStatistics in interface Ehcache

getStatisticsAccuracy

public int getStatisticsAccuracy()

Accurately measuring statistics can be expensive. Returns the current accuracy setting.

Specified by:

getStatisticsAccuracy in interface Ehcache

Returns:

one of Statistics.STATISTICS_ACCURACY_BEST_EFFORT, Statistics.STATISTICS_ACCURACY_GUARANTEED, Statistics.STATISTICS_ACCURACY_NONE

setStatisticsAccuracy

public void setStatisticsAccuracy(int statisticsAccuracy)

Sets the statistics accuracy.

Specified by:

setStatisticsAccuracy in interface Ehcache

Parameters:

statisticsAccuracy - one of Statistics.STATISTICS_ACCURACY_BEST_EFFORT, Statistics.STATISTICS_ACCURACY_GUARANTEED, Statistics.STATISTICS_ACCURACY_NONE

evictExpiredElements

public void evictExpiredElements()

Causes all elements stored in the Cache to be synchronously checked for expiry, and if expired, evicted.

Specified by:

evictExpiredElements in interface Ehcache

isKeyInCache

public boolean isKeyInCache(java.lang.Object key)

An inexpensive check to see if the key exists in the cache.

Specified by:

isKeyInCache in interface Ehcache

Parameters:

key - the key to check for

Returns:

true if an Element matching the key is found in the cache. No assertions are made about the state of the Element.

isValueInCache

public boolean isValueInCache(java.lang.Object value)

An extremely expensive check to see if the value exists in the cache.

Specified by:

isValueInCache in interface Ehcache

Parameters:

value - to check for

Returns:

true if an Element matching the key is found in the cache. No assertions are made about the state of the Element.

getStatistics

public Statistics getStatistics()
                         throws java.lang.IllegalStateException

Gets an immutable Statistics object representing the Cache statistics at the time. How the statistics are calculated depends on the statistics accuracy setting. The only aspect of statistics sensitive to the accuracy setting is object size. How that is calculated is discussed below.

Best Effort Size

This result is returned when the statistics accuracy setting is Statistics.STATISTICS_ACCURACY_BEST_EFFORT.

The size is the number of Elements in the MemoryStore plus the number of Elements in the DiskStore.

This number is the actual number of elements, including expired elements that have not been removed. Any duplicates between stores are accounted for.

Expired elements are removed from the the memory store when getting an expired element, or when attempting to spool an expired element to disk.

Expired elements are removed from the disk store when getting an expired element, or when the expiry thread runs, which is once every five minutes.

Guaranteed Accuracy Size

This result is returned when the statistics accuracy setting is Statistics.STATISTICS_ACCURACY_GUARANTEED.

This method accounts for elements which might be expired or duplicated between stores. It take approximately 200ms per 1000 elements to execute.

Fast but non-accurate Size

This result is returned when the statistics accuracy setting is Statistics.STATISTICS_ACCURACY_NONE.

The number given may contain expired elements. In addition if the DiskStore is used it may contain some double counting of elements. It takes 6ms for 1000 elements to execute. Time to execute is O(log n). 50,000 elements take 36ms.

Specified by:

getStatistics in interface Ehcache

Returns:

the number of elements in the ehcache, with a varying degree of accuracy, depending on accuracy setting.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

setCacheManager

public void setCacheManager(CacheManager cacheManager)

Sets the CacheManager

Specified by:

setCacheManager in interface Ehcache

Parameters:

cacheManager -

getBootstrapCacheLoader

public BootstrapCacheLoader getBootstrapCacheLoader()

Accessor for the BootstrapCacheLoader associated with this cache. For testing purposes.

Specified by:

getBootstrapCacheLoader in interface Ehcache

Returns:

the BootstrapCacheLoader to use

setBootstrapCacheLoader

public void setBootstrapCacheLoader(BootstrapCacheLoader bootstrapCacheLoader)
                             throws CacheException

Sets the bootstrap cache loader.

Specified by:

setBootstrapCacheLoader in interface Ehcache

Parameters:

bootstrapCacheLoader - the loader to be used

Throws:

CacheException - if this method is called after the cache is initialized

setDiskStorePath

public void setDiskStorePath(java.lang.String diskStorePath)
                      throws CacheException

DiskStore paths can conflict between CacheManager instances. This method allows the path to be changed.

Specified by:

setDiskStorePath in interface Ehcache

Parameters:

diskStorePath - the new path to be used.

Throws:

CacheException - if this method is called after the cache is initialized

initialise

public void initialise()

Newly created caches do not have a MemoryStore or a DiskStore.

This method creates those and makes the cache ready to accept elements

Specified by:

initialise in interface Ehcache

bootstrap

public void bootstrap()

Bootstrap command. This must be called after the Cache is intialised, during CacheManager initialisation. If loads are synchronous, they will complete before the CacheManager initialise completes, otherwise they will happen in the background.

Specified by:

bootstrap in interface Ehcache

dispose

public void dispose()
             throws java.lang.IllegalStateException

Flushes all cache items from memory to auxilliary caches and close the auxilliary caches.

Should be invoked only by CacheManager.

Specified by:

dispose in interface Ehcache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

getCacheConfiguration

public CacheConfiguration getCacheConfiguration()

Gets the cache configuration this cache was created with.

Things like listeners that are added dynamically are excluded.

Specified by:

getCacheConfiguration in interface Ehcache

get

public Element get(java.lang.Object key)
            throws java.lang.RuntimeException,
                   LockTimeoutException

Looks up an entry. Blocks if the entry is null until a call to put(net.sf.ehcache.Element) is done to put an Element in.

If a put is not done, the lock is never released.

If this method throws an exception, it is the responsibility of the caller to catch that exception and call put(new Element(key, null)); to release the lock acquired. See SelfPopulatingCache for an example. Note. If a LockTimeoutException is thrown while doing a get(java.lang.Object) it means the lock was never acquired, therefore it is a threading error to call put(net.sf.ehcache.Element)

Specified by:

get in interface Ehcache

Parameters:

key - an Object value

Returns:

the element, or null, if it does not exist.

Throws:

LockTimeoutException - if timeout millis is non zero and this method has been unable to acquire a lock in that time

java.lang.RuntimeException - if thrown the lock will not released. Catch and callput(new Element(key, null)); to release the lock acquired.

See Also:

Ehcache.isExpired(net.sf.ehcache.Element)

getLockForKey

protected Mutex getLockForKey(java.lang.Object key)

Gets the Mutex to use for a given key.

Parameters:

key - the key

Returns:

one of a limited number of Mutexes.

put

public void put(Element element)

Adds an entry and unlocks it

Specified by:

put in interface Ehcache

Parameters:

element - An object. If Serializable it can fully participate in replication and the DiskStore.

put

public void put(Element element,
                boolean doNotNotifyCacheReplicators)
         throws java.lang.IllegalArgumentException,
                java.lang.IllegalStateException,
                CacheException

Put an element in the cache.

Resets the access statistics on the element, which would be the case if it has previously been gotten from a cache, and is now being put back.

Also notifies the CacheEventListener that:

• the element was put, but only if the Element was actually put.
• if the element exists in the cache, that an update has occurred, even if the element would be expired if it was requested

Specified by:

put in interface Ehcache

Parameters:

element - An object. If Serializable it can fully participate in replication and the DiskStore.

doNotNotifyCacheReplicators - whether the put is coming from a doNotNotifyCacheReplicators cache peer, in which case this put should not initiate a further notification to doNotNotifyCacheReplicators cache peers

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

java.lang.IllegalArgumentException - if the element is null

CacheException

putQuiet

public void putQuiet(Element element)
              throws java.lang.IllegalArgumentException,
                     java.lang.IllegalStateException,
                     CacheException

Put an element in the cache, without updating statistics, or updating listeners. This is meant to be used in conjunction with getQuiet(java.io.Serializable)

Specified by:

putQuiet in interface Ehcache

Parameters:

element - An object. If Serializable it can fully participate in replication and the DiskStore.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

java.lang.IllegalArgumentException - if the element is null

CacheException

get

public Element get(java.io.Serializable key)
            throws java.lang.IllegalStateException,
                   CacheException

Gets an element from the cache. Updates Element Statistics

Note that the Element's lastAccessTime is always the time of this get. Use getQuiet(Object) to peak into the Element to see its last access time with get

Specified by:

get in interface Ehcache

Parameters:

key - a serializable value

Returns:

the element, or null, if it does not exist.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

See Also:

isExpired(net.sf.ehcache.Element)

getQuiet

public Element getQuiet(java.io.Serializable key)
                 throws java.lang.IllegalStateException,
                        CacheException

Gets an element from the cache, without updating Element statistics. Cache statistics are still updated.

Specified by:

getQuiet in interface Ehcache

Parameters:

key - a serializable value

Returns:

the element, or null, if it does not exist.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

See Also:

isExpired(net.sf.ehcache.Element)

getQuiet

public Element getQuiet(java.lang.Object key)
                 throws java.lang.IllegalStateException,
                        CacheException

Gets an element from the cache, without updating Element statistics. Cache statistics are still updated.

Specified by:

getQuiet in interface Ehcache

Parameters:

key - a serializable value

Returns:

the element, or null, if it does not exist.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

Since:

1.2

See Also:

isExpired(net.sf.ehcache.Element)

getKeys

public java.util.List getKeys()
                       throws CacheException

Returns the keys for this cache.

Specified by:

getKeys in interface Ehcache

Returns:

a list of Object keys for this cache. This is not a live set, so it will not track changes to the key set.

Throws:

CacheException

getKeysWithExpiryCheck

public java.util.List getKeysWithExpiryCheck()
                                      throws java.lang.IllegalStateException,
                                             CacheException

Returns a list of all elements in the cache. Only keys of non-expired elements are returned.

The returned keys are unique and can be considered a set.

The List returned is not live. It is a copy.

The time taken is O(n), where n is the number of elements in the cache. On a 1.8Ghz P4, the time taken is approximately 200ms per 1000 entries. This method is not synchronized, because it relies on a non-live list returned from getKeys() , which is synchronised, and which takes 8ms per 1000 entries. This way cache liveness is preserved, even if this method is very slow to return.

Consider whether your usage requires checking for expired keys. Because this method takes so long, depending on cache settings, the list could be quite out of date by the time you get it.

Specified by:

getKeysWithExpiryCheck in interface Ehcache

Returns:

a list of Object keys

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

getKeysNoDuplicateCheck

public java.util.List getKeysNoDuplicateCheck()
                                       throws java.lang.IllegalStateException

Returns a list of all elements in the cache, whether or not they are expired.

The returned keys are not unique and may contain duplicates. If the cache is only using the memory store, the list will be unique. If the disk store is being used as well, it will likely contain duplicates, because of the internal store design.

The List returned is not live. It is a copy.

The time taken is O(log n). On a single cpu 1.8Ghz P4, approximately 6ms is required for 1000 entries and 36 for 50000.

This is the fastest getKeys method

Specified by:

getKeysNoDuplicateCheck in interface Ehcache

Returns:

a list of Object keys

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

remove

public boolean remove(java.io.Serializable key)
               throws java.lang.IllegalStateException

Removes an Element from the Cache. This also removes it from any stores it may be in.

Also notifies the CacheEventListener after the element was removed, but only if an Element with the key actually existed.

Specified by:

remove in interface Ehcache

Parameters:

key -

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

remove

public boolean remove(java.lang.Object key)
               throws java.lang.IllegalStateException

Removes an Element from the Cache. This also removes it from any stores it may be in.

Also notifies the CacheEventListener after the element was removed, but only if an Element with the key actually existed.

Specified by:

remove in interface Ehcache

Parameters:

key -

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

Since:

1.2

remove

public boolean remove(java.io.Serializable key,
                      boolean doNotNotifyCacheReplicators)
               throws java.lang.IllegalStateException

Removes an Element from the Cache. This also removes it from any stores it may be in.

Also notifies the CacheEventListener after the element was removed, but only if an Element with the key actually existed.

Specified by:

remove in interface Ehcache

Parameters:

key -

doNotNotifyCacheReplicators - whether the put is coming from a doNotNotifyCacheReplicators cache peer, in which case this put should not initiate a further notification to doNotNotifyCacheReplicators cache peers

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

remove

public boolean remove(java.lang.Object key,
                      boolean doNotNotifyCacheReplicators)
               throws java.lang.IllegalStateException

Removes an Element from the Cache. This also removes it from any stores it may be in.

Also notifies the CacheEventListener after the element was removed, but only if an Element with the key actually existed.

Specified by:

remove in interface Ehcache

Parameters:

key -

doNotNotifyCacheReplicators - whether the put is coming from a doNotNotifyCacheReplicators cache peer, in which case this put should not initiate a further notification to doNotNotifyCacheReplicators cache peers

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

removeQuiet

public boolean removeQuiet(java.io.Serializable key)
                    throws java.lang.IllegalStateException

Removes an Element from the Cache, without notifying listeners. This also removes it from any stores it may be in.

Specified by:

removeQuiet in interface Ehcache

Parameters:

key -

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

removeQuiet

public boolean removeQuiet(java.lang.Object key)
                    throws java.lang.IllegalStateException

Removes an Element from the Cache, without notifying listeners. This also removes it from any stores it may be in.

Specified by:

removeQuiet in interface Ehcache

Parameters:

key -

Returns:

true if the element was removed, false if it was not found in the cache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

Since:

1.2

removeAll

public void removeAll()
               throws java.lang.IllegalStateException,
                      CacheException

Removes all cached items.

Specified by:

removeAll in interface Ehcache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

removeAll

public void removeAll(boolean doNotNotifyCacheReplicators)
               throws java.lang.IllegalStateException,
                      CacheException

Removes all cached items.

Specified by:

removeAll in interface Ehcache

Parameters:

doNotNotifyCacheReplicators - whether the put is coming from a doNotNotifyCacheReplicators cache peer, in which case this put should not initiate a further notification to doNotNotifyCacheReplicators cache peers

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

flush

public void flush()
           throws java.lang.IllegalStateException,
                  CacheException

Flushes all cache items from memory to the disk store, and from the DiskStore to disk.

Specified by:

flush in interface Ehcache

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

getSize

public int getSize()
            throws java.lang.IllegalStateException,
                   CacheException

Gets the size of the cache. This is a subtle concept. See below.

The size is the number of Elements in the MemoryStore plus the number of Elements in the DiskStore.

This number is the actual number of elements, including expired elements that have not been removed.

Expired elements are removed from the the memory store when getting an expired element, or when attempting to spool an expired element to disk.

Expired elements are removed from the disk store when getting an expired element, or when the expiry thread runs, which is once every five minutes.

To get an exact size, which would exclude expired elements, use getKeysWithExpiryCheck().size(), although see that method for the approximate time that would take.

To get a very fast result, use getKeysNoDuplicateCheck().size(). If the disk store is being used, there will be some duplicates.

Specified by:

getSize in interface Ehcache

Returns:

The size value

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

CacheException

calculateInMemorySize

public long calculateInMemorySize()
                           throws java.lang.IllegalStateException,
                                  CacheException

Gets the size of the memory store for this cache

Warning: This method can be very expensive to run. Allow approximately 1 second per 1MB of entries. Running this method could create liveness problems because the object lock is held for a long period

Specified by:

calculateInMemorySize in interface Ehcache

Returns:

the approximate size of the memory store in bytes

Throws:

java.lang.IllegalStateException

CacheException

getMemoryStoreSize

public long getMemoryStoreSize()
                        throws java.lang.IllegalStateException

Returns the number of elements in the memory store.

Specified by:

getMemoryStoreSize in interface Ehcache

Returns:

the number of elements in the memory store

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

getDiskStoreSize

public int getDiskStoreSize()
                     throws java.lang.IllegalStateException

Returns the number of elements in the disk store.

Specified by:

getDiskStoreSize in interface Ehcache

Returns:

the number of elements in the disk store.

Throws:

java.lang.IllegalStateException - if the cache is not Status.STATUS_ALIVE

getStatus

public Status getStatus()

Gets the status attribute of the Cache.

Specified by:

getStatus in interface Ehcache

Returns:

The status value from the Status enum class

liveness

public java.lang.String liveness()

Synchronized version of getName to test liveness of the object lock.

The time taken for this method to return is a useful measure of runtime contention on the cache.

setTimeoutMillis

public void setTimeoutMillis(int timeoutMillis)

Sets the time to wait to acquire a lock. This may be modified at any time.

The consequences of setting a timeout are:

1. if a lock cannot be acquired in the given time a LockTimeoutException is thrown.
2. if there is a queue of threads waiting for the first thread to complete, but it does not complete within the time out period, the successive threads may find that they have exceeded their lock timeouts and fail. This is usually a good thing because it stops a build up of threads from overwhelming a busy resource, but it does need to be considered in the design of user interfaces. The timeout should be set no greater than the time a user would be expected to wait before considering the action will never return
3. it will be common to see a number of threads timeout trying to get the same lock. This is a normal and desired consequence.

The consequences of not setting a timeout (or setting it to 0) are:

1. There are no partial failures in the system. But there is a greater possibility that a temporary overload in one part of the system can cause a back up that may take a long time to recover from.
2. A failing method that perhaps fails because a resource is overloaded will be hit by each thread in turn, no matter whether there is a still a user who cares about getting a response.

Parameters:

timeoutMillis - the time in ms. Must be a positive number. 0 means wait forever.

getTimeoutMillis

public int getTimeoutMillis()

Gets the time to wait to acquire a lock.

Returns:

the time in ms.

registerCacheExtension

public void registerCacheExtension(CacheExtension cacheExtension)

Register a CacheExtension with the cache. It will then be tied into the cache lifecycle.

Specified by:

registerCacheExtension in interface Ehcache

unregisterCacheExtension

public void unregisterCacheExtension(CacheExtension cacheExtension)

Unregister a CacheExtension with the cache. It will then be detached from the cache lifecycle.

Specified by:

unregisterCacheExtension in interface Ehcache

getAverageGetTime

public float getAverageGetTime()

The average get time in ms.

Specified by:

getAverageGetTime in interface Ehcache

setCacheExceptionHandler

public void setCacheExceptionHandler(CacheExceptionHandler cacheExceptionHandler)

Sets an ExceptionHandler on the Cache. If one is already set, it is overwritten.

Specified by:

setCacheExceptionHandler in interface Ehcache

getCacheExceptionHandler

public CacheExceptionHandler getCacheExceptionHandler()

Sets an ExceptionHandler on the Cache. If one is already set, it is overwritten.

Specified by:

getCacheExceptionHandler in interface Ehcache

setCacheLoader

public void setCacheLoader(CacheLoader cacheLoader)

This method is not appropriate to use with BlockingCache.

Specified by:

setCacheLoader in interface Ehcache

Parameters:

cacheLoader - the loader to dynamically load new cache entries

getCacheLoader

public CacheLoader getCacheLoader()

Gets the CacheLoader registered in this cache

Specified by:

getCacheLoader in interface Ehcache

Returns:

the loader, or null if there is none

getWithLoader

public Element getWithLoader(java.lang.Object key,
                             CacheLoader loader,
                             java.lang.Object loaderArgument)
                      throws CacheException

This method is not appropriate to use with BlockingCache.

Specified by:

getWithLoader in interface Ehcache

Parameters:

key - key whose associated value is to be returned.

loader - the override loader to use. If null, the cache's default loader will be used

loaderArgument - an argument to pass to the CacheLoader.

Returns:

an element if it existed or could be loaded, otherwise null

Throws:

CacheException - if this method is called

getAllWithLoader

public java.util.Map getAllWithLoader(java.util.Collection keys,
                                      java.lang.Object loaderArgument)
                               throws CacheException

This method is not appropriate to use with BlockingCache.

Specified by:

getAllWithLoader in interface Ehcache

Parameters:

keys - a collection of keys to be returned/loaded

loaderArgument - an argument to pass to the CacheLoader.

Returns:

a Map populated from the Cache. If there are no elements, an empty Map is returned.

Throws:

CacheException - if this method is called

load

public void load(java.lang.Object key)
          throws CacheException

This method is not appropriate to use with BlockingCache.

Specified by:

load in interface Ehcache

Parameters:

key - key whose associated value to be loaded using the associated cacheloader if this cache doesn't contain it.

Throws:

CacheException - if this method is called

loadAll

public void loadAll(java.util.Collection keys,
                    java.lang.Object argument)
             throws CacheException

This method is not appropriate to use with BlockingCache.

Specified by:

loadAll in interface Ehcache

Throws:

CacheException - if this method is called

isDisabled

public boolean isDisabled()

Whether this cache is disabled. "Disabled" means:

1. bootstrap is disabled
2. puts are discarded
3. putQuites are discarded

In all other respects the cache continues as it is.

You can disable and enable a cache programmatically through the setDisabled(boolean) method.

By default caches are enabled on creation, unless the net.sf.ehcache.disabled system property is set.

Specified by:

isDisabled in interface Ehcache

Returns:

true if the cache is disabled.

setDisabled

public void setDisabled(boolean disabled)

Disables or enables this cache. This call overrides the previous value of disabled, even if the net.sf.ehcache.disabled system property is set

Specified by:

setDisabled in interface Ehcache

Parameters:

disabled - true if you wish to disable, false to enable

See Also:

isDisabled()