EvictionPolicy


1   /*
2    * JBoss, the OpenSource J2EE webOS
3    *
4    * Distributable under LGPL license.
5    * See terms of license at gnu.org.
6    */
7   package org.jboss.cache.eviction;
8   
9   import org.jboss.cache.CacheImpl;
10  import org.jboss.cache.Fqn;
11  
12  import java.util.Set  ;
13  
14  /**
15   * Generic eviction policy interface.
16   * <p/>
17   * None of the Eviction classes are thread safe. It is assumed that an individual instance of an EvictionPolicy/
18   * EvictionAlgorithm/EvictionQueue/EvictionConfiguration are only operated on by one thread at any given time.
19   *
20   * @author Ben Wang 2-2004
21   * @author Daniel Huang - dhuang@jboss.org - 10/2005
22   */
23  public interface EvictionPolicy
24  {
25     /**
26      * Evict a node form the underlying cache.
27      *
28      * @param fqn DataNode corresponds to this fqn.
29      * @throws Exception
30      */
31     void evict(Fqn fqn) throws Exception  ;
32  
33     /**
34      * Return children names as Objects
35      *
36      * @param fqn
37      * @return Child names under given fqn
38      */
39     Set   getChildrenNames(Fqn fqn);
40  
41     /**
42      * Is this a leaf node?
43      *
44      * @param fqn
45      * @return true/false if leaf node.
46      */
47     boolean hasChild(Fqn fqn);
48  
49     Object   getCacheData(Fqn fqn, Object   key);
50  
51     /**
52      * Method called to configure this implementation.
53      */
54     void configure(CacheImpl cache);
55  
56     /**
57      * Get the associated EvictionAlgorithm used by the EvictionPolicy.
58      * <p/>
59      * This relationship should be 1-1.
60      *
61      * @return An EvictionAlgorithm implementation.
62      */
63     EvictionAlgorithm getEvictionAlgorithm();
64  
65     /**
66      * The EvictionPolicyConfig implementation class used by this EvictionPolicy.
67      *
68      * @return EvictionPolicyConfig implementation class.
69      */
70     Class  <EvictionPolicyConfig> getEvictionConfigurationClass();
71  
72     /**
73      * This method will be invoked prior to an event being processed for a node
74      * with the specified Fqn.
75      * <p/>
76      * This method provides a way to optimize the performance of eviction by
77      * signalling that the node associated with the specified Fqn should not be
78      * subject to normal eviction processing.  It can also be used to filter
79      * out certain {@link NodeEventType event types} in which the particular
80      * eviction algorithm has no interest.
81      * </p>
82      * <p/>
83      * If this method returns false then the event is processed normally
84      * and eviction processing for the node continues. As a result, the event
85      * will be added to the {@link org.jboss.cache.Region eviction region's} event queue where
86      * at some later point the particular algorithm of the eviction policy
87      * can use it to decide whether to call {@link #evict(Fqn)}.
88      * </p>
89      * <p/>
90      * If this method returns true, then the event is ignored and will not factor
91      * in any subsequent eviction processing.
92      * </p>
93      *
94      * @param fqn       The Fqn of the node associated with the event.
95      * @param eventType the type of the event
96      * @return <code>true</code> to ignore events of this type for this Fqn,
97      *         <code>false</code> to process events normally.
98      */
99     boolean canIgnoreEvent(Fqn fqn, NodeEventType eventType);
100 }
101
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