package org.apache.ojb.otm.lock.isolation;

 /* Copyright 2003-2005 The Apache Software Foundation

  *

  * 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.

  */

 import java.util.Collection;

 import java.util.Iterator;

 import org.apache.ojb.otm.core.Transaction;

 import org.apache.ojb.otm.lock.LockingException;

 import org.apache.ojb.otm.lock.ObjectLock;

 public class RepeatableReadIsolation extends AbstractIsolation

 {

     /**

      * @see org.apache.ojb.otm.lock.isolation.TransactionIsolation#readLock(Transaction, ObjectLock)

      */

     public void readLock(Transaction tx, ObjectLock lock)

         throws LockingException

     {

         Transaction writer = lock.getWriter();

         if (writer == null)

         {

             lock.readLock(tx);

             if (lock.getWriter() != null)

             {

                 lock.releaseLock(tx);

                 readLock(tx, lock);

             }

         }

         else if (tx != writer)

         {

             lock.waitForTx(writer);

             readLock(tx, lock);

         }

         // else if tx is the writer, it can also read.

     }

     /**

      * @see org.apache.ojb.otm.lock.isolation.TransactionIsolation#writeLock(Transaction, ObjectLock)

      */

     public void writeLock(Transaction tx, ObjectLock lock)

         throws LockingException

     {

         Collection readers = lock.getReaders();

         if (!readers.isEmpty())

         {

             for (Iterator it = readers.iterator(); it.hasNext(); )

             {

                 Transaction reader = (Transaction) it.next();

                 if (reader != tx)

                 {

                     lock.waitForTx(reader);

                     writeLock(tx, lock);

                     return;

                 }

             }

         }

         lock.writeLock(tx);

         readers = lock.getReaders();

         if (readers.size() > 1)

         {

             lock.releaseLock(tx);

             writeLock(tx, lock);

         }

     }

 }