com.trivago.triava.tcache.eviction

Class FreezingEvictor<K,V>

java.lang.Object

com.trivago.triava.tcache.eviction.FreezingEvictor<K,V>

Type Parameters:

K - The key class

V - The value class

All Implemented Interfaces:

EvictionInterface<K,V>, Serializable

Direct Known Subclasses:

ClockEviction, LFUEviction, LRUEviction

public abstract class FreezingEvictor<K,V>
extends Object
implements EvictionInterface<K,V>

Convenience class that implements EvictionInterface. The evictionComparator() returns a default Comparator, so custom implementations that extend FreezingEvictor only need to implement getFreezeValue(Object, TCacheHolder)

Author:

cesken

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
FreezingEvictor()

Method Summary

Modifier and Type	Method and Description
void	afterEviction() Default implementation for EvictionInterface.afterEviction().
void	beforeEviction() Default implementation for EvictionInterface.beforeEviction().
int	compareByFreezer(HolderFreezer<K,V> o1, HolderFreezer<K,V> o2, boolean includeTiebreaker) Compare objects by their frozen value HolderFreezer.getFrozenValue().
Comparator<HolderFreezer<K,V>>	evictionComparator() Returns the standard comparator, which compares first the frozen values, and (on ties) uses the tiebreaker.
abstract long	getFreezeValue(K key, TCacheHolder<V> holder) Returns a value for the given key, that may be used by the concrete implementation of the #evictionComparator().

Methods inherited from class java.lang.Object

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

Constructor Detail

FreezingEvictor

public FreezingEvictor()

Method Detail

evictionComparator

public Comparator<HolderFreezer<K,V>> evictionComparator()

Returns the standard comparator, which compares first the frozen values, and (on ties) uses the tiebreaker. When overriding this comparator, one can still use this functionality, by calling compareByFreezer(HolderFreezer, HolderFreezer, boolean) in the own comparator.

Specified by:

evictionComparator in interface EvictionInterface<K,V>

Returns:

The comparator implementing the eviction policy

beforeEviction

public void beforeEviction()

Default implementation for EvictionInterface.beforeEviction(). It does nothing.

Specified by:

beforeEviction in interface EvictionInterface<K,V>

afterEviction

public void afterEviction()

Default implementation for EvictionInterface.afterEviction(). It does nothing.

Specified by:

afterEviction in interface EvictionInterface<K,V>

getFreezeValue

public abstract long getFreezeValue(K key,
                                    TCacheHolder<V> holder)

Returns a value for the given key, that may be used by the concrete implementation of the #evictionComparator(). The default comparator returned by FreezingEvictor#evictionComparator() chooses keys with smaller values to be evicted sooner than those with bigger values (comparable to Comparator.compare(Object, Object)). While it is recommended to conform to this, it is not required - own implementations may use any other strategy, but should document this clearly.

There are three typical usage patterns:

• MUST implement: There is a relevant mutable value, for example metadata like use count or the last use timestamp. In this case you MUST implement this method.
• SHOULD implement: The relevant value is expensive to calculate. In this case you SHOULD implement this method for performance reasons, as the value is likely required many times during sorting.
• NOT USED: For other cases, this method should return 0.

If the implementing class does not require such a value, it should return 0. Typical examples are element metadata like use count or the last use timestamp. Content-aware eviction implementations can also derive a value from the data, like session status ("logged out", "idle").

Specified by:

getFreezeValue in interface EvictionInterface<K,V>

Parameters:

key - The key

holder - The holder that holds the associated value for the key

Returns:

The eviction relevance, see method description.

compareByFreezer

public int compareByFreezer(HolderFreezer<K,V> o1,
                            HolderFreezer<K,V> o2,
                            boolean includeTiebreaker)

Compare objects by their frozen value HolderFreezer.getFrozenValue(). The returned value is negative, 0, or positive, similar to o1.getFrozenValue().compareTo(o2.getFrozenValue()). The tie breaker in the HolderFreezer will be taken into account, if includeTiebreaker is set.

Parameters:

o1 - The first object for the comparison

o2 - The second object for the comparison

includeTiebreaker - If true, the tie breaker will be consulted on identical elements

Returns:

A compare value, as explained in the method description