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There is a newer version: 5.7.1

/**
 * 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 locking;

import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Simulates some external resource that can only be access by one process at a time
 */
public class FakeLimitedResource
{
    private final AtomicBoolean     inUse = new AtomicBoolean(false);

    public void     use() throws InterruptedException
    {
        // in a real application this would be accessing/manipulating a shared resource

        if ( !inUse.compareAndSet(false, true) )
        {
            throw new IllegalStateException("Needs to be used by one client at a time");
        }

        try
        {
            Thread.sleep((long)(3 * Math.random()));
        }
        finally
        {
            inUse.set(false);
        }
    }
}