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 *     http://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     * Gets the {@code Synchronizer} used by this object. An implementation must not return <b>null</b>. If no
039     * {@code Synchronizer} has been set so far, a meaningful default {@code Synchronizer} has to be returned.
040     *
041     * @return the {@code Synchronizer} used by this object
042     */
043    Synchronizer getSynchronizer();
044
045    /**
046     * Locks this object for the specified mode. This call may block until this object is released from other lock
047     * operations. When it returns the caller can access the object in a way compatible to the specified {@code LockMode}.
048     * When done the {@code unlock()} must be called with the same {@code LockMode} argument. In practice, a
049     * <b>try</b>-<b>finally</b> construct should be used as in the following example:
050     *
051     * <pre>
052     * SynchronizerSupport syncSupport = ...;
053     * syncSupport.lock(LockMode.READ);
054     * try
055     * {
056     *     // read access to syncSupport
057     * }
058     * finally
059     * {
060     *     syncSupport.unlock(LockMode.READ);
061     * }
062     * </pre>
063     *
064     * <em>Note:</em> Always use this method for obtaining a lock rather than accessing the object's {@link Synchronizer}
065     * directly. An implementation may perform additional actions which are not executed when only interacting with the
066     * {@code Synchronizer}.
067     *
068     * @param mode the {@code LockMode}
069     */
070    void lock(LockMode mode);
071
072    /**
073     * Sets the {@code Synchronizer} to be used by this object. Calling this method and setting an appropriate
074     * {@code Synchronizer} determines whether this object can be accessed in a thread-safe way or not. The argument may be
075     * <b>null</b>; in this case an implementation should switch to a default {@code Synchronizer}.
076     *
077     * @param sync the {@code Synchronizer} for this object
078     */
079    void setSynchronizer(Synchronizer sync);
080
081    /**
082     * Releases a lock of this object that was obtained using the {@link #lock(LockMode)} method. This method must always be
083     * called pair-wise with {@code lock()}. The argument must match to the one passed to the corresponding {@code lock()}
084     * call; otherwise, the behavior of the {@link Synchronizer} is unspecified.
085     *
086     * @param mode the {@code LockMode}
087     */
088    void unlock(LockMode mode);
089}