Source code: org/apache/derby/iapi/services/cache/Cacheable.java
1 /*
2
3 Derby - Class org.apache.derby.iapi.services.cache.Cacheable
4
5 Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable.
6
7 Licensed under the Apache License, Version 2.0 (the "License");
8 you may not use this file except in compliance with the License.
9 You may obtain a copy of the License at
10
11 http://www.apache.org/licenses/LICENSE-2.0
12
13 Unless required by applicable law or agreed to in writing, software
14 distributed under the License is distributed on an "AS IS" BASIS,
15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 See the License for the specific language governing permissions and
17 limitations under the License.
18
19 */
20
21 package org.apache.derby.iapi.services.cache;
22
23 import org.apache.derby.iapi.error.StandardException;
24
25 /**
26 Any object that implements this interface can be cached using the services of
27 the CacheManager/CacheFactory. In addition to implementing this interface the
28 class must be public and it must have a public no-arg constructor. This is because
29 the cache manager will construct objects itself and then set their identity
30 by calling the setIdentity method.
31 <P>
32 A Cacheable object has five states:
33 <OL>
34 <OL>
35 <LI> No identity - The object is only accessable by the cache manager
36 <LI> Identity, clean, unkept - The object has an identity, is clean but is only accessable by the cache manager
37 <LI> Identity, clean, kept - The object has an identity, is clean, and is in use by one or more threads
38 <LI> Identity, kept, dirty - The object has an identity, is dirty, and is in use by one or more threads
39 <LI> Identity, unkept, dirty - The object has an identity, is dirty but is only accessable by the cache manager
40 </OL>
41 </OL>
42 <BR>
43 While the object is kept it is guaranteed
44 not to change identity. While it is unkept no-one outside of the
45 cache manager can have a reference to the object.
46 The cache manager returns kept objects and they return to the unkept state
47 when all the current users of the object have released it.
48 <BR>
49 It is required that the object can only move into a dirty state while it is kept.
50
51 <BR> MT - Mutable : thread aware - Calls to Cacheable method must only be made by the
52 cache manager or the object itself.
53
54 @see CacheManager
55 @see CacheFactory
56 @see Class#newInstance
57 */
58 public interface Cacheable {
59
60 /**
61 Set the identity of the object.
62 <p>
63 Set the identity of the object to represent an item that already exists,
64 e.g. an existing container.
65 The object will be in the No Identity state,
66 ie. it will have just been created or clearIdentity() was just called.
67 <BR>
68 The object must copy the information out of key, not just store a reference to key.
69 After this call the expression getIdentity().equals(key) must return true.
70 <BR>
71 If the class of the object needs to change (e.g. to support a different format)
72 then the object should create a new object, call its initParameter() with the parameters
73 the original object was called with, set its identity and return a reference to it. The cache
74 manager will discard the reference to the old object.
75 <BR>
76 If an exception is thrown the object must be left in the no-identity state.
77
78 <BR> MT - single thread required - Method must only be called be cache manager
79 and the cache manager will guarantee only one thread can be calling it.
80
81 @return an object reference if the object can take on the identity, null otherwise.
82
83 @exception StandardException Standard Cloudscape Policy
84
85 @see CacheManager#find
86
87 */
88 public Cacheable setIdentity(Object key) throws StandardException;
89
90 /**
91 Create a new item.
92 <p>
93 Create a new item and set the identity of the object to represent it.
94 The object will be in the No Identity state,
95 ie. it will have just been created or clearIdentity() was just called.
96 <BR>
97 The object must copy the information out of key, not just store a reference to key
98 if the key is not immutable.
99 After this call the expression getIdentity().equals(key) must return true.
100 <BR>
101 <BR>
102 If the class of the object needs to change (e.g. to support a different format)
103 then the object should create a new object, call its initParameter() with the parameters
104 the original object was called with, set its identity and return a reference to it. The cache
105 manager will discard the reference to the old object.
106 <BR>
107 If an exception is thrown the object must be left in the no-identity state.
108
109 <BR> MT - single thread required - Method must only be called be cache manager
110 and the cache manager will guarantee only one thread can be calling it.
111
112 @return an object reference if the object can take on the identity, null otherwise.
113
114 @exception StandardException If forCreate is true and the object cannot be created.
115
116 @see CacheManager#create
117
118 */
119 public Cacheable createIdentity(Object key, Object createParameter) throws StandardException;
120
121
122 /**
123 Put the object into the No Identity state.
124
125 <BR> MT - single thread required - Method must only be called be cache manager
126 and the cache manager will guarantee only one thread can be calling it.
127
128 */
129 public void clearIdentity();
130
131 /**
132 Get the identity of this object.
133
134 <BR> MT - thread safe.
135
136 */
137 public Object getIdentity();
138
139
140 /**
141 Returns true of the object is dirty.
142 May be called when the object is kept or unkept.
143
144 <BR> MT - thread safe
145
146 */
147 public boolean isDirty();
148
149 /**
150 Clean the object.
151 It is up to the object to ensure synchronization of the isDirty()
152 and clean() method calls.
153 <BR>
154 If forRemove is true then the
155 object is being removed due to an explict remove request, in this case
156 the cache manager will have called this method regardless of the
157 state of the isDirty()
158
159 <BR>
160 If an exception is thrown the object must be left in the clean state.
161
162 <BR> MT - thread safe - Can be called at any time by the cache manager, it is the
163 responsibility of the object implementing Cacheable to ensure any users of the
164 object do not conflict with the clean call.
165
166 @exception StandardException Standard Cloudscape error policy.
167
168 */
169 public void clean(boolean forRemove) throws StandardException;
170 }
171