org.castor.cache.hashbelt

Class AbstractHashbelt

public abstract class AbstractHashbelt extends AbstractBaseCache

An abstract, core implementation of the hashbelt functionality; individual implementations will differ on the underlying behavior.

A hashbelt has six important values which get set at initialization:

containers
The number of containers in the conveyor belt. For example: If a box will drop off of the conveyor belt every 30 seconds, and you want a cache that lasts for 5 minutes, you want 5 / 30 = 6 containers on the belt. Every 30 seconds, another, clean container goes on the front of the conveyor belt, and everything in the last belt gets discarded. If not specified 10 containers are used by default.
For systems with fine granularity, you are free to use a large number of containers; but the system is most efficient when the user decides on a "sweet spot" determining both the number of containers to be managed on the whole and the optimal number of buckets in those containers for managing. This is ultimately a performance/accuracy tradeoff with the actual discard-from-cache time being further from the mark as the rotation time goes up. Also the number of objects discarded at once when capacity limit is reached depends upon the number of containers.
capacity
Maximum capacity of the whole cache. If there are, for example, ten containers on the belt and the capacity has been set to 1000, each container will hold a maximum of 1000/10 objects. Therefore if the capacity limit is reached and the last container gets droped from the belt there are up to 100 objects discarted at once. By default the capacity is set to 0 which causes capacity limit to be ignored so the cache can hold an undefined number of objects.
ttl
The maximum time an object lifes in cache. If the are, for example, ten containers and ttl is set to 300 seconds (5 minutes), a new container will be put in front of the belt every 300/10 = 30 seconds while another is dropped at the end at the same time. Due to the granularity of 30 seconds, everything just until 5 minutes 30 seconds will also end up in this box. The default value for ttl is 60 seconds. If ttl is set to 0 which means that objects life in cache for unlimited time and may only discarded by a capacity limit.
monitor
The monitor intervall in minutes when hashbelt cache rports the current number of containers used and objects cached. If set to 0 (default) monitoring is disabled.
container-class
The implementation of org.castor.cache.hashbelt.container.Container interface to be used for all containers of the cache. Castor provides the following 3 implementations of the Container interface.
org.castor.cache.hashbelt.container.FastIteratingContainer
org.castor.cache.hashbelt.container.MapContainer
org.castor.cache.hashbelt.container.WeakReferenceContainer
If not specified the MapContainer will be used as default.
reaper-class
Specific reapers yield different behaviors. The GC reaper, the default, just dumps the contents to the garbage collector. However, custom implementations may want to actually do something when a bucket drops off the end; see the javadocs on other available reapers to find a reaper strategy that meets your behavior requirements. Apart of the default org.castor.cache.hashbelt.reaper.NullReaper we provide 3 abstract implementations of org.castor.cahe.hashbelt.reaper.Reaper interface:
org.castor.cache.hashbelt.reaper.NotifyingReaper
org.castor.cache.hashbelt.reaper.RefreshingReaper
org.castor.cache.hashbelt.reaper.ReinsertingReaper
to be extended by your custom implementation.

Since: 1.0

Version: $Revision: 6320 $ $Date: 2006-04-25 16:09:10 -0600 (Tue, 25 Apr 2006) $

Author: Gregory Block Ralf Joachim

Field Summary
static intDEFAULT_CAPACITY
Default capacity of cache.
static intDEFAULT_CONTAINERS
Default number of containers for cache.
static ClassDEFAULT_CONTAINER_CLASS
Default container class.
static intDEFAULT_MONITOR
Default monitor interval of cache in minutes.
static ClassDEFAULT_REAPER_CLASS
Default reaper class.
static intDEFAULT_TTL
Default ttl of cache in seconds.
static StringPARAM_CAPACITY
Mapped initialization parameter: capacity
static StringPARAM_CONTAINERS
Mapped initialization parameter: containers
static StringPARAM_CONTAINER_CLASS
Mapped initialization parameter: container-class
static StringPARAM_MONITOR
Mapped initialization parameter: monitor
static StringPARAM_REAPER_CLASS
Mapped initialization parameter: reaper-class
static StringPARAM_TTL
Mapped initialization parameter: ttl
Method Summary
voidclear()
voidclose()
booleancontainsKey(Object key)
booleancontainsValue(Object value)
SetentrySet()
intgetCapacity()
Get real capacity of this cache.
protected ObjectgetObjectFromCache(Object key)
Get object currently associated with given key from cache.
intgetTTL()
Get real ttl of this cache.
voidinitialize(Properties params)
booleanisEmpty()
SetkeySet()
protected ReadWriteLocklock()
Get reference to the ReadWriteLock of this cache instance.
protected ObjectputObjectIntoCache(Object key, Object value)
Put given value with given key in cache.
protected ObjectremoveObjectFromCache(Object key)
Remove any available association for given key.
intsize()
Collectionvalues()

Field Detail

DEFAULT_CAPACITY

public static final int DEFAULT_CAPACITY
Default capacity of cache.

DEFAULT_CONTAINERS

public static final int DEFAULT_CONTAINERS
Default number of containers for cache.

DEFAULT_CONTAINER_CLASS

public static final Class DEFAULT_CONTAINER_CLASS
Default container class.

DEFAULT_MONITOR

public static final int DEFAULT_MONITOR
Default monitor interval of cache in minutes.

DEFAULT_REAPER_CLASS

public static final Class DEFAULT_REAPER_CLASS
Default reaper class.

DEFAULT_TTL

public static final int DEFAULT_TTL
Default ttl of cache in seconds.

PARAM_CAPACITY

public static final String PARAM_CAPACITY
Mapped initialization parameter: capacity

PARAM_CONTAINERS

public static final String PARAM_CONTAINERS
Mapped initialization parameter: containers

PARAM_CONTAINER_CLASS

public static final String PARAM_CONTAINER_CLASS
Mapped initialization parameter: container-class

PARAM_MONITOR

public static final String PARAM_MONITOR
Mapped initialization parameter: monitor

PARAM_REAPER_CLASS

public static final String PARAM_REAPER_CLASS
Mapped initialization parameter: reaper-class

PARAM_TTL

public static final String PARAM_TTL
Mapped initialization parameter: ttl

Method Detail

clear

public final void clear()
{@inheritDoc }

See Also: java.util.Map#clear()

close

public final void close()
{@inheritDoc }

See Also: close

containsKey

public final boolean containsKey(Object key)
{@inheritDoc }

See Also: java.util.Map#containsKey(java.lang.Object)

containsValue

public final boolean containsValue(Object value)
{@inheritDoc }

See Also: java.util.Map#containsValue(java.lang.Object)

entrySet

public final Set entrySet()
{@inheritDoc }

See Also: java.util.Map#entrySet()

getCapacity

public final int getCapacity()
Get real capacity of this cache.

Returns: Real capacity of this cache.

getObjectFromCache

protected final Object getObjectFromCache(Object key)
Get object currently associated with given key from cache. Take care to acquire a read or write lock before calling this method and release the lock thereafter.

Parameters: key The key to return the associated object for.

Returns: The object associated with given key.

getTTL

public final int getTTL()
Get real ttl of this cache.

Returns: Real ttl of this cache.

initialize

public final void initialize(Properties params)
{@inheritDoc }

See Also: initialize

isEmpty

public final boolean isEmpty()
{@inheritDoc }

See Also: java.util.Map#isEmpty()

keySet

public final Set keySet()
{@inheritDoc }

See Also: java.util.Map#keySet()

lock

protected final ReadWriteLock lock()
Get reference to the ReadWriteLock of this cache instance.

Returns: ReadWriteLock to synchronize access to cache.

putObjectIntoCache

protected final Object putObjectIntoCache(Object key, Object value)
Put given value with given key in cache. Return the object previously associated with key. Take care to acquire a write lock before calling this method and release the lock thereafter.

Parameters: key The key to associate the given value with. value The value to associate with given key.

Returns: The object previously associated with given key. null will be returned if no value has been associated with key.

removeObjectFromCache

protected final Object removeObjectFromCache(Object key)
Remove any available association for given key. Take care to acquire a write lock before calling this method and release the lock thereafter.

Parameters: key The key to remove any previously associate value for.

Returns: The object previously associated with given key. null will be returned if no value has been associated with key.

size

public final int size()
{@inheritDoc }

See Also: java.util.Map#size()

values

public final Collection values()
{@inheritDoc }

See Also: java.util.Map#values()

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