# ReadLockConcern.java

    /*
     * Copyright 2007-2011 Rickard Oberg.
     * Copyright 2007-2012 Niclas Hedhman.
     *
     * Licensed  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 read-lock to Composite
     */
    @AppliesTo( ReadLock.class )
    public class ReadLockConcern
        extends ConcernOf<InvocationHandler>
        implements InvocationHandler
    {
        private
        @This
        ReadWriteLock lock;

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

        /**
         * Fix for this bug:
         * http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6822370
         *
         * @param lock the lock to be acquired.
         */
        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
                }
            }
        }
    }