1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.sync;
18
19 /**
20 * <p>
21 * Definition of an interface for objects that can be associated with a {@link Synchronizer}.
22 * </p>
23 * <p>
24 * This interface defines methods for querying and setting the {@code Synchronizer}. In addition, it is possible to lock
25 * the object for a certain operation. This is useful if some complex operations are to be performed on the
26 * {@code SynchronizerSupport} object in an atomic way.
27 * </p>
28 * <p>
29 * Note that the actual effect of these methods depends on the concrete {@code Synchronizer} implementation in use! If
30 * only a dummy {@code Synchronizer} is involved (which is appropriate if objects are only accessed by a single thread),
31 * locking an object does not really prohibit concurrent access.
32 * </p>
33 *
34 * @since 2.0
35 */
36 public interface SynchronizerSupport {
37
38 /**
39 * Gets the {@code Synchronizer} used by this object. An implementation must not return <strong>null</strong>. If no
40 * {@code Synchronizer} has been set so far, a meaningful default {@code Synchronizer} has to be returned.
41 *
42 * @return the {@code Synchronizer} used by this object
43 */
44 Synchronizer getSynchronizer();
45
46 /**
47 * Locks this object for the specified mode. This call may block until this object is released from other lock
48 * operations. When it returns the caller can access the object in a way compatible to the specified {@code LockMode}.
49 * When done the {@code unlock()} must be called with the same {@code LockMode} argument. In practice, a
50 * <strong>try</strong>-<strong>finally</strong> construct should be used as in the following example:
51 *
52 * <pre>
53 * SynchronizerSupport syncSupport = ...;
54 * syncSupport.lock(LockMode.READ);
55 * try
56 * {
57 * // read access to syncSupport
58 * }
59 * finally
60 * {
61 * syncSupport.unlock(LockMode.READ);
62 * }
63 * </pre>
64 *
65 * <em>Note:</em> Always use this method for obtaining a lock rather than accessing the object's {@link Synchronizer}
66 * directly. An implementation may perform additional actions which are not executed when only interacting with the
67 * {@code Synchronizer}.
68 *
69 * @param mode the {@code LockMode}
70 */
71 void lock(LockMode mode);
72
73 /**
74 * Sets the {@code Synchronizer} to be used by this object. Calling this method and setting an appropriate
75 * {@code Synchronizer} determines whether this object can be accessed in a thread-safe way or not. The argument may be
76 * <strong>null</strong>; in this case an implementation should switch to a default {@code Synchronizer}.
77 *
78 * @param sync the {@code Synchronizer} for this object
79 */
80 void setSynchronizer(Synchronizer sync);
81
82 /**
83 * Releases a lock of this object that was obtained using the {@link #lock(LockMode)} method. This method must always be
84 * called pair-wise with {@code lock()}. The argument must match to the one passed to the corresponding {@code lock()}
85 * call; otherwise, the behavior of the {@link Synchronizer} is unspecified.
86 *
87 * @param mode the {@code LockMode}
88 */
89 void unlock(LockMode mode);
90 }