ReadyState.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 com.sun.jini.thread;

import java.rmi.NoSuchObjectException;
import java.rmi.RemoteException;

/**
 * Utility class used to prevent access to a service before it has completed
 * its initialization or after it starts to shutdown.  Each public entry point 
 * to the service should call <code>check</code> or <code>shutdown</code>, 
 * and initialization should call <code>ready</code> when the service is ready
 * to use.
 *  
 * @author Sun Microsystems, Inc.
 * @since 2.1
 */
public class ReadyState {
    // flag to indicate the service is initializing
    private static final int INITIALIZE = 0;
    // flag to indicate the service is ready to use
    private static final int READY = 1;
    // flag to indicate the service is shutting down
    private static final int SHUTDOWN = 2;
    
    private int state = INITIALIZE;

    /**
     * Checks if the service is ready to use, waiting if it is
     * initializing, and throwing <code>NoSuchObjectException</code> if it is 
     * shutting down.  Note that the <code>NoSuchObjectException</code> will be 
     * wrapped in a <code>RemoteExceptionWrapper</code>.
     */
    public synchronized void check() {
	while (true) {
	    switch (state) {
		case INITIALIZE:
		    try {
			wait();
		    } catch (InterruptedException e) {}
		    break;
		case READY:
		    return;
		default:
		    throw new RemoteExceptionWrapper(new NoSuchObjectException(
			  "service is unavailable"));
	    }
	}
    }

    /**
     * Marks the service ready for use.  This method should only be called
     * from the code that performs the service initialization, and it should
     * only be called once.
     */
    public synchronized void ready() {
	switch (state) {
	    case INITIALIZE:
		state = READY;
		notifyAll();
		break;
	    default:
		throw new AssertionError("ready is only called when the"
					 + " service is in the INITIALIZE"
					 + " state");
	}
    }

    /**
     * Marks the service as shutting down, waiting if it is initializing,
     * and throwing <code>NoSuchObjectException</code> if it is already 
     * shutting down.  Note that the <code>NoSuchObjectException</code> will be 
     * wrapped in a <code>RemoteExceptionWrapper</code>.
     */
    public synchronized void shutdown() {
	check();
	state = SHUTDOWN;
	notifyAll();
    }

    /**
     * Wrapper used to prevent a <code>RemoteException</code> from being
     * wrapped in a <code>ServerException</code> by the RMI implementation.
     */
    private static class RemoteExceptionWrapper extends RuntimeException {
    	/** added for consistency; this will never be used */
    	private static final long serialVersionUID = 1L;
	/** the exception that will be written to the output stream */
	private final RemoteException wrapped;
	/** Simple constructor */
	public RemoteExceptionWrapper(RemoteException wrapped) {
	    this.wrapped = wrapped;
	}
	/** returns the exception to marshal */
	private Object writeReplace() {
	    return wrapped;
	}	
    }
}