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 * @since 2.0 039 */ 040public interface SynchronizerSupport 041{ 042 /** 043 * Returns the {@code Synchronizer} used by this object. An implementation 044 * must not return <b>null</b>. If no {@code Synchronizer} has been set so 045 * far, a meaningful default {@code Synchronizer} has to be returned. 046 * 047 * @return the {@code Synchronizer} used by this object 048 */ 049 Synchronizer getSynchronizer(); 050 051 /** 052 * Sets the {@code Synchronizer} to be used by this object. Calling this 053 * method and setting an appropriate {@code Synchronizer} determines whether 054 * this object can be accessed in a thread-safe way or not. The argument may 055 * be <b>null</b>; in this case an implementation should switch to a default 056 * {@code Synchronizer}. 057 * 058 * @param sync the {@code Synchronizer} for this object 059 */ 060 void setSynchronizer(Synchronizer sync); 061 062 /** 063 * Locks this object for the specified mode. This call may block until this 064 * object is released from other lock operations. When it returns the caller 065 * can access the object in a way compatible to the specified 066 * {@code LockMode}. When done the {@code unlock()} must be called with the 067 * same {@code LockMode} argument. In practice, a <b>try</b>-<b>finally</b> 068 * construct should be used as in the following example: 069 * 070 * <pre> 071 * SynchronizerSupport syncSupport = ...; 072 * syncSupport.lock(LockMode.READ); 073 * try 074 * { 075 * // read access to syncSupport 076 * } 077 * finally 078 * { 079 * syncSupport.unlock(LockMode.READ); 080 * } 081 * </pre> 082 * 083 * <em>Note:</em> Always use this method for obtaining a lock rather than 084 * accessing the object's {@link Synchronizer} directly. An implementation 085 * may perform additional actions which are not executed when only 086 * interacting with the {@code Synchronizer}. 087 * 088 * @param mode the {@code LockMode} 089 */ 090 void lock(LockMode mode); 091 092 /** 093 * Releases a lock of this object that was obtained using the 094 * {@link #lock(LockMode)} method. This method must always be called 095 * pair-wise with {@code lock()}. The argument must match to the one passed 096 * to the corresponding {@code lock()} call; otherwise, the behavior of the 097 * {@link Synchronizer} is unspecified. 098 * 099 * @param mode the {@code LockMode} 100 */ 101 void unlock(LockMode mode); 102}