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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 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 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 write operation. This may cause other waiting threads to be granted
* access to the managed configuration.
*/
void endWrite();
}