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 022 * {@link Synchronizer}. 023 * </p> 024 * <p> 025 * This interface defines methods for querying and setting the 026 * {@code Synchronizer}. In addition, it is possible to lock the object for a 027 * certain operation. This is useful if some complex operations are to be 028 * performed on the {@code SynchronizerSupport} object in an atomic way. 029 * </p> 030 * <p> 031 * Note that the actual effect of these methods depends on the concrete 032 * {@code Synchronizer} implementation in use! If only a dummy 033 * {@code Synchronizer} is involved (which is appropriate if objects are only 034 * accessed by a single thread), locking an object does not really prohibit 035 * concurrent access. 036 * </p> 037 * 038 * @version $Id: SynchronizerSupport.java 1624601 2014-09-12 18:04:36Z oheger $ 039 * @since 2.0 040 */ 041public interface SynchronizerSupport 042{ 043 /** 044 * Returns the {@code Synchronizer} used by this object. An implementation 045 * must not return <b>null</b>. If no {@code Synchronizer} has been set so 046 * far, a meaningful default {@code Synchronizer} has to be returned. 047 * 048 * @return the {@code Synchronizer} used by this object 049 */ 050 Synchronizer getSynchronizer(); 051 052 /** 053 * Sets the {@code Synchronizer} to be used by this object. Calling this 054 * method and setting an appropriate {@code Synchronizer} determines whether 055 * this object can be accessed in a thread-safe way or not. The argument may 056 * be <b>null</b>; in this case an implementation should switch to a default 057 * {@code Synchronizer}. 058 * 059 * @param sync the {@code Synchronizer} for this object 060 */ 061 void setSynchronizer(Synchronizer sync); 062 063 /** 064 * Locks this object for the specified mode. This call may block until this 065 * object is released from other lock operations. When it returns the caller 066 * can access the object in a way compatible to the specified 067 * {@code LockMode}. When done the {@code unlock()} must be called with the 068 * same {@code LockMode} argument. In practice, a <b>try</b>-<b>finally</b> 069 * construct should be used as in the following example: 070 * 071 * <pre> 072 * SynchronizerSupport syncSupport = ...; 073 * syncSupport.lock(LockMode.READ); 074 * try 075 * { 076 * // read access to syncSupport 077 * } 078 * finally 079 * { 080 * syncSupport.unlock(LockMode.READ); 081 * } 082 * </pre> 083 * 084 * <em>Note:</em> Always use this method for obtaining a lock rather than 085 * accessing the object's {@link Synchronizer} directly. An implementation 086 * may perform additional actions which are not executed when only 087 * interacting with the {@code Synchronizer}. 088 * 089 * @param mode the {@code LockMode} 090 */ 091 void lock(LockMode mode); 092 093 /** 094 * Releases a lock of this object that was obtained using the 095 * {@link #lock(LockMode)} method. This method must always be called 096 * pair-wise with {@code lock()}. The argument must match to the one passed 097 * to the corresponding {@code lock()} call; otherwise, the behavior of the 098 * {@link Synchronizer} is unspecified. 099 * 100 * @param mode the {@code LockMode} 101 */ 102 void unlock(LockMode mode); 103}