001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.xbean.kernel;
018    
019    /**
020     * A ServiceContion represents a prerequsite for a service to start or stop.  A condition can be added to a service with
021     * the {@link ServiceFactory#addStartCondition(ServiceCondition)} or
022     * {@link ServiceFactory#addStopCondition(ServiceCondition)} methods.
023     *
024     * @author Dain Sundstrom
025     * @version $Id$
026     * @since 2.0
027     */
028    public interface ServiceCondition {
029        /**
030         * Initializes the condition.  The conition is now allowed reserve unique resources and start threads.
031         * mehtod should never block the thread nor should it throw any exceptions.
032         * </p>
033         * Note: this method is called from within a critical lock within the kernel, so do not block the thread or
034         * call back into the kernel.  This method should never throw an exception.
035         *
036         * @param context context information for this condition
037         */
038        void initialize(ServiceConditionContext context);
039    
040        /**
041         * Gets statisfied state of this conditon.  Once a condition returns true from this method it is assumed to be satisfied until
042         * destroyed and reinitialized.
043         * </p>
044         * Note: this method is called from within a critical lock within the kernel, so do not block the thread or
045         * call back into the kernel.  This method should never throw an exception.
046         *
047         * @return true if this condition is satisfied; false otherwise
048         */
049        boolean isSatisfied();
050    
051        /**
052         * Destroys the condition.  The condition must release all resources and stop any started threads.
053         * </p>
054         * Note: this method is called from within a critical lock within the kernel, so do not block the thread or
055         * call back into the kernel.  This method should never throw an exception.
056         */
057        void destroy();
058    }