tuwien.auto.calimero.buffer.cache
Class ExpiringCache

java.lang.Object
  tuwien.auto.calimero.buffer.cache.ExpiringCache

All Implemented Interfaces:

Cache

Direct Known Subclasses:

LFUCache, PositiveListCache

public abstract class ExpiringCache
extends java.lang.Object
implements Cache

Implements a cache expiring mechanism for CacheObjects.

A time span is specified for how long a value is considered valid. After that time for expiring, the cache object is removed on the next call of removeExpired() by an internal CacheSweeper. If a cache with expiring cache objects is not used anymore, invoke Cache.clear() to quit the running cache sweeping mechanism.
The timestamp of CacheObject.getTimestamp() is used to determine if a cache object value has expired.
Note that if the timestamp of a CacheObject changes after it was put into the cache, the object has to be reinserted (see Cache.put(CacheObject)) to keep the cache in a consistent state. If no expiring is used, this might be omitted.

Nested Class Summary

Nested classes/interfaces inherited from interface tuwien.auto.calimero.buffer.cache.Cache

Cache.Statistic

Field Summary

protected static int	defaultSweepInterval Default sweep interval in seconds used for a CacheSweeper (60 seconds).
protected java.util.Map	map The map holding the CacheObjects.
protected int	sweepInterval Sweep interval in seconds used for the CacheSweeper.

Constructor Summary

ExpiringCache(int timeToExpire)
Creates an ExpiringCache.

Method Summary

protected void	notifyRemoved(CacheObject obj) Override this method to get notified when removeExpired() removed a CacheObject from the map.
void	removeExpired() Removes all CacheObjects, where CacheObject.getTimestamp() + timeToExpire <= now, with timeToExpire > 0 and now is the point of time removeExpired() is invoked.
protected void	startSweeper() Starts a new CacheSweeper, if not already running, and if an expiring time for CacheObject was specified.
protected void	stopSweeper() Stops the CacheSweeper, if any.

Methods inherited from class java.lang.Object

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

Methods inherited from interface tuwien.auto.calimero.buffer.cache.Cache

clear, get, put, remove, statistic

Field Detail

defaultSweepInterval

protected static final int defaultSweepInterval

Default sweep interval in seconds used for a CacheSweeper (60 seconds).

See Also:

Constant Field Values

map

protected java.util.Map map

The map holding the CacheObjects.

The map instance itself is not synchronized, synchronization is done using the cache object (this).

sweepInterval

protected int sweepInterval

Sweep interval in seconds used for the CacheSweeper.

It defaults to 60 seconds. For a new value to take effect, it has to be assigned either before the first startSweeper() call, or the cache sweeper has to be restarted.

Constructor Detail

ExpiringCache

public ExpiringCache(int timeToExpire)

Creates an ExpiringCache.

Note that for the actual begin of cache sweeping startSweeper() has to be invoked.

Parameters:

timeToExpire - time > 0 in seconds for cache entries to stay valid, on time = 0 no expiring of cache entries will occur

Method Detail

notifyRemoved

protected void notifyRemoved(CacheObject obj)

Override this method to get notified when removeExpired() removed a CacheObject from the map.

Parameters:

obj - removed CacheObject

removeExpired

public void removeExpired()

Removes all CacheObjects, where
CacheObject.getTimestamp() + timeToExpire <= now, with timeToExpire > 0 and now is the point of time removeExpired() is invoked.
If no expiring time was specified at creation of cache, no cache object will be expired.

Specified by:

removeExpired in interface Cache

startSweeper

protected final void startSweeper()

Starts a new CacheSweeper, if not already running, and if an expiring time for CacheObject was specified.
If the methods startSweeper and stopSweeper are invoked by different threads, they need to be synchronized.

stopSweeper

protected final void stopSweeper()

Stops the CacheSweeper, if any.