libraries/locking/src/main/java/org/qi4j/library/locking/WriteLockConcern.java

/*
 * 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.qi4j.library.locking;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import org.qi4j.api.common.AppliesTo;
import org.qi4j.api.concern.ConcernOf;
import org.qi4j.api.injection.scope.This;

/**
 * Applies write-lock to Composite
 */
@AppliesTo( WriteLock.class )
public class WriteLockConcern
    extends ConcernOf<InvocationHandler>
    implements InvocationHandler
{
    private
    @This
    ReadWriteLock lock;

    @Override
    public Object invoke( Object o, Method method, Object[] objects )
        throws Throwable
    {
        Lock writeLock = lock.writeLock();
        lock(writeLock);
        try
        {
            return next.invoke( o, method, objects );
        }
        finally
        {
            writeLock.unlock();
        }
    }

    /**
     * Fix for this bug:
     * http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6822370
     */
    protected void lock(Lock lock)
    {
        while(true)
        {
            try
            {
                //noinspection StatementWithEmptyBody
                while( !lock.tryLock( 1000, TimeUnit.MILLISECONDS ) )
                {
                    // On timeout, try again
                }
                return; // Finally got a lock
            }
            catch( InterruptedException e )
            {
                // Try again
            }
        }
    }
}