1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.configuration2.sync; 18 19 /** 20 * <p> 21 * An interface controlling synchronization of configuration instances. 22 * </p> 23 * <p> 24 * Each {@code Configuration} object derived from {@link org.apache.commons.configuration2.AbstractConfiguration 25 * AbstractConfiguration} has an associated {@code Synchronizer} object. Before an operation on the configuration is 26 * performed (e.g. a property read or an update), the {@code Synchronizer} is invoked. Depending on the concrete 27 * implementation of the {@code Synchronizer} used, the configuration can be made thread-safe. 28 * </p> 29 * <p> 30 * Whether a configuration has to be thread-safe or not is a matter of a concrete use case. For instance, an application 31 * that just reads some configuration settings on startup does need a thread-safe configuration implementation. A 32 * configuration in contrast which is shared between multiple components and updated concurrently should better be 33 * thread-safe. In order to satisfy both kinds of use cases, the support for thread-safety has been extracted out of the 34 * configuration implementation and refactored into this {@code Synchronizer} interface. By assigning different 35 * {@code Synchronizer} implementations to a configuration instance, the instance's support for concurrent access can be 36 * adapted to the concrete use case. 37 * </p> 38 * <p> 39 * The methods defined by this interface are similar to a <em>read-write lock</em>. The {@code Synchronizer} is notified 40 * when read or write operations start and end. A concrete implementation can then apply a specific policy to decide 41 * when threads need to block or when access to the configuration for the desired operation is granted. 42 * </p> 43 * 44 * @since 2.0 45 */ 46 public interface Synchronizer { 47 /** 48 * Notifies this {@code Synchronizer} that the current thread is going to start a read operation on the managed 49 * configuration. This call can block if a concrete implementation decides that the thread has to wait until a specific 50 * condition is fulfilled. 51 */ 52 void beginRead(); 53 54 /** 55 * Notifies this {@code Synchronizer} that the current thread is going to start a write operation on the managed 56 * configuration. This call may block. For instance, a concrete implementation may suspend the thread until all read 57 * operations currently active are finished, 58 */ 59 void beginWrite(); 60 61 /** 62 * Notifies this {@code Synchronizer} that the current thread has finished its read operation. This may cause other 63 * waiting threads to be granted access to the managed configuration. 64 */ 65 void endRead(); 66 67 /** 68 * Notifies this {@code Synchronizer} that the current thread has finished its write operation. This may cause other 69 * waiting threads to be granted access to the managed configuration. 70 */ 71 void endWrite(); 72 }