org.ovirt.engine.api.common.util

Class ReapedMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

java.util.HashMap<K,V>

org.ovirt.engine.api.common.util.ReapedMap<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

public class ReapedMap<K,V>
extends HashMap<K,V>

Models a strongly-referenced primary hash map, coupled with a reapable secondary map based on soft-referenced values (rather than keys, as is the case with the java.util.WeakHashMap). Use this like a normal hash map, but when values need no longer be retained they should be marked as reapable so that they are made eligible for garbage collection. Entries are finally evicted if not already GC'd before the expiry of the reapAfter timeout (calculated either from the point at which it was marked reapable or the last time of access). Freeing of the entry prior to this timeout expiring is at the discretion of the garbage collector and depends on whether the JVM is experiencing memory pressure, the type of JVM selected (the client JVM uses much more aggressive GC policies that the server variant) and also the JVM options controlling the heap size. REVISIT: does the world really need yet another hand-rolled cache type? REVISIT: inherited entrySet() etc. don't take account of secondary

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Constructor Summary

Constructors

Constructor and Description
ReapedMap()
ReapedMap(long reapAfter)
ReapedMap(long reapAfter, boolean accessBasedAging)

Method Summary

Methods

Modifier and Type	Method and Description
void	clear()
V	get(Object key)
V	put(K k, V v)
void	reapable(K k) Mark a key as being reapable, caching corresponding soft reference to corresponding value in the secondary map.
long	reapableSize()
V	remove(Object key)

Methods inherited from class java.util.HashMap

clone, containsKey, containsValue, entrySet, isEmpty, keySet, putAll, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

equals, hashCode

Constructor Detail

ReapedMap

public ReapedMap()

ReapedMap

public ReapedMap(long reapAfter)

Parameters:

reapAfter - entries become eligible for reaping after this duration (ms)

ReapedMap

public ReapedMap(long reapAfter,
         boolean accessBasedAging)

Parameters:

reapAfter - entries become eligible for reaping after this duration (ms)

accessBasedAging - reset reapAfter timeout on each access

Method Detail

get

public V get(Object key)

Specified by:

get in interface Map<K,V>

Overrides:

get in class HashMap<K,V>

put

public V put(K k,
    V v)

Specified by:

put in interface Map<K,V>

Overrides:

put in class HashMap<K,V>

remove

public V remove(Object key)

Specified by:

remove in interface Map<K,V>

Overrides:

remove in class HashMap<K,V>

clear

public void clear()

Specified by:

clear in interface Map<K,V>

Overrides:

clear in class HashMap<K,V>

reapable

public void reapable(K k)

Mark a key as being reapable, caching corresponding soft reference to corresponding value in the secondary map.

Parameters:

k -

reapableSize

public long reapableSize()

Returns:

the size of the secondary map