/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.sync;

/**
 * <p>
 * Definition of an interface for objects that can be associated with a {@link Synchronizer}.
 * </p>
 * <p>
 * This interface defines methods for querying and setting the {@code Synchronizer}. In addition, it is possible to lock
 * the object for a certain operation. This is useful if some complex operations are to be performed on the
 * {@code SynchronizerSupport} object in an atomic way.
 * </p>
 * <p>
 * Note that the actual effect of these methods depends on the concrete {@code Synchronizer} implementation in use! If
 * only a dummy {@code Synchronizer} is involved (which is appropriate if objects are only accessed by a single thread),
 * locking an object does not really prohibit concurrent access.
 * </p>
 *
 * @since 2.0
 */
public interface SynchronizerSupport {
    /**
     * Gets the {@code Synchronizer} used by this object. An implementation must not return <b>null</b>. If no
     * {@code Synchronizer} has been set so far, a meaningful default {@code Synchronizer} has to be returned.
     *
     * @return the {@code Synchronizer} used by this object
     */
    Synchronizer getSynchronizer();

    /**
     * Locks this object for the specified mode. This call may block until this object is released from other lock
     * operations. When it returns the caller can access the object in a way compatible to the specified {@code LockMode}.
     * When done the {@code unlock()} must be called with the same {@code LockMode} argument. In practice, a
     * <b>try</b>-<b>finally</b> construct should be used as in the following example:
     *
     * <pre>
     * SynchronizerSupport syncSupport = ...;
     * syncSupport.lock(LockMode.READ);
     * try
     * {
     *     // read access to syncSupport
     * }
     * finally
     * {
     *     syncSupport.unlock(LockMode.READ);
     * }
     * </pre>
     *
     * <em>Note:</em> Always use this method for obtaining a lock rather than accessing the object's {@link Synchronizer}
     * directly. An implementation may perform additional actions which are not executed when only interacting with the
     * {@code Synchronizer}.
     *
     * @param mode the {@code LockMode}
     */
    void lock(LockMode mode);

    /**
     * Sets the {@code Synchronizer} to be used by this object. Calling this method and setting an appropriate
     * {@code Synchronizer} determines whether this object can be accessed in a thread-safe way or not. The argument may be
     * <b>null</b>; in this case an implementation should switch to a default {@code Synchronizer}.
     *
     * @param sync the {@code Synchronizer} for this object
     */
    void setSynchronizer(Synchronizer sync);

    /**
     * Releases a lock of this object that was obtained using the {@link #lock(LockMode)} method. This method must always be
     * called pair-wise with {@code lock()}. The argument must match to the one passed to the corresponding {@code lock()}
     * call; otherwise, the behavior of the {@link Synchronizer} is unspecified.
     *
     * @param mode the {@code LockMode}
     */
    void unlock(LockMode mode);
}
