# 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
                }
            }
        }
    }