001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.sync;
018
019/**
020 * <p>
021 * Definition of an interface for objects that can be associated with a {@link Synchronizer}.
022 * </p>
023 * <p>
024 * This interface defines methods for querying and setting the {@code Synchronizer}. In addition, it is possible to lock
025 * the object for a certain operation. This is useful if some complex operations are to be performed on the
026 * {@code SynchronizerSupport} object in an atomic way.
027 * </p>
028 * <p>
029 * Note that the actual effect of these methods depends on the concrete {@code Synchronizer} implementation in use! If
030 * only a dummy {@code Synchronizer} is involved (which is appropriate if objects are only accessed by a single thread),
031 * locking an object does not really prohibit concurrent access.
032 * </p>
033 *
034 * @since 2.0
035 */
036public interface SynchronizerSupport {
037
038    /**
039     * Gets the {@code Synchronizer} used by this object. An implementation must not return <strong>null</strong>. If no
040     * {@code Synchronizer} has been set so far, a meaningful default {@code Synchronizer} has to be returned.
041     *
042     * @return the {@code Synchronizer} used by this object
043     */
044    Synchronizer getSynchronizer();
045
046    /**
047     * Locks this object for the specified mode. This call may block until this object is released from other lock
048     * operations. When it returns the caller can access the object in a way compatible to the specified {@code LockMode}.
049     * When done the {@code unlock()} must be called with the same {@code LockMode} argument. In practice, a
050     * <strong>try</strong>-<strong>finally</strong> construct should be used as in the following example:
051     *
052     * <pre>
053     * SynchronizerSupport syncSupport = ...;
054     * syncSupport.lock(LockMode.READ);
055     * try
056     * {
057     *     // read access to syncSupport
058     * }
059     * finally
060     * {
061     *     syncSupport.unlock(LockMode.READ);
062     * }
063     * </pre>
064     *
065     * <em>Note:</em> Always use this method for obtaining a lock rather than accessing the object's {@link Synchronizer}
066     * directly. An implementation may perform additional actions which are not executed when only interacting with the
067     * {@code Synchronizer}.
068     *
069     * @param mode the {@code LockMode}
070     */
071    void lock(LockMode mode);
072
073    /**
074     * Sets the {@code Synchronizer} to be used by this object. Calling this method and setting an appropriate
075     * {@code Synchronizer} determines whether this object can be accessed in a thread-safe way or not. The argument may be
076     * <strong>null</strong>; in this case an implementation should switch to a default {@code Synchronizer}.
077     *
078     * @param sync the {@code Synchronizer} for this object
079     */
080    void setSynchronizer(Synchronizer sync);
081
082    /**
083     * Releases a lock of this object that was obtained using the {@link #lock(LockMode)} method. This method must always be
084     * called pair-wise with {@code lock()}. The argument must match to the one passed to the corresponding {@code lock()}
085     * call; otherwise, the behavior of the {@link Synchronizer} is unspecified.
086     *
087     * @param mode the {@code LockMode}
088     */
089    void unlock(LockMode mode);
090}