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/*
* 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;
/**
*
* An interface controlling synchronization of configuration instances.
*
*
* Each {@code Configuration} object derived from {@link org.apache.commons.configuration2.AbstractConfiguration
* AbstractConfiguration} has an associated {@code Synchronizer} object. Before an operation on the configuration is
* performed (e.g. a property read or an update), the {@code Synchronizer} is invoked. Depending on the concrete
* implementation of the {@code Synchronizer} used, the configuration can be made thread-safe.
*
*
* Whether a configuration has to be thread-safe or not is a matter of a concrete use case. For instance, an application
* that just reads some configuration settings on startup does need a thread-safe configuration implementation. A
* configuration in contrast which is shared between multiple components and updated concurrently should better be
* thread-safe. In order to satisfy both kinds of use cases, the support for thread-safety has been extracted out of the
* configuration implementation and refactored into this {@code Synchronizer} interface. By assigning different
* {@code Synchronizer} implementations to a configuration instance, the instance's support for concurrent access can be
* adapted to the concrete use case.
*
*
* The methods defined by this interface are similar to a read-write lock. The {@code Synchronizer} is notified
* when read or write operations start and end. A concrete implementation can then apply a specific policy to decide
* when threads need to block or when access to the configuration for the desired operation is granted.
*
*
* @since 2.0
*/
public interface Synchronizer {
/**
* Notifies this {@code Synchronizer} that the current thread is going to start a read operation on the managed
* configuration. This call can block if a concrete implementation decides that the thread has to wait until a specific
* condition is fulfilled.
*/
void beginRead();
/**
* Notifies this {@code Synchronizer} that the current thread is going to start a write operation on the managed
* configuration. This call may block. For instance, a concrete implementation may suspend the thread until all read
* operations currently active are finished,
*/
void beginWrite();
/**
* Notifies this {@code Synchronizer} that the current thread has finished its read operation. This may cause other
* waiting threads to be granted access to the managed configuration.
*/
void endRead();
/**
* Notifies this {@code Synchronizer} that the current thread has finished its write operation. This may cause other
* waiting threads to be granted access to the managed configuration.
*/
void endWrite();
}