# SynchronizedCompositeMethodInstancePool.java

    /*
     * Copyright (c) 2008, Rickard Öberg. All Rights Reserved.
     *
     * 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.runtime.composite;

    /**
     * Method instance pool that keeps a linked list. Uses synchronization
     * to ensure that instances are acquired and returned in a thread-safe
     * manner.
     */
    public final class SynchronizedCompositeMethodInstancePool
        implements InstancePool<CompositeMethodInstance>
    {
        private CompositeMethodInstance first = null;

        @Override
        public synchronized CompositeMethodInstance obtainInstance()
        {
            CompositeMethodInstance instance = first;
            if( instance != null )
            {
                first = instance.getNext();
            }
            return instance;
        }

        @Override
        public synchronized void releaseInstance( CompositeMethodInstance instance )
        {
            instance.setNext( first );
            first = instance;
        }
    }