Guard.java

/*
 * Copyright (c) 2002, 2003, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package org.jboss.com.sun.corba.se.spi.orbutil.fsm;

/**
 * 
 * @author Ken Cavanaugh
 */
public interface Guard
{
    public static final class Complement extends GuardBase
    {
        private Guard guard;

        public Complement(GuardBase guard)
        {
            super("not(" + guard.getName() + ")");
            this.guard = guard;
        }

        public Result evaluate(FSM fsm, Input in)
        {
            return guard.evaluate(fsm, in).complement();
        }
    }

    public static final class Result
    {
        private String name;

        private Result(String name)
        {
            this.name = name;
        }

        public static Result convert(boolean res)
        {
            return res ? ENABLED : DISABLED;
        }

        public Result complement()
        {
            if (this == ENABLED)
                return DISABLED;
            else if (this == DISABLED)
                return ENABLED;
            else
                return DEFERED;
        }

        public String toString()
        {
            return "Guard.Result[" + name + "]";
        }

        public static final Result ENABLED = new Result("ENABLED");

        public static final Result DISABLED = new Result("DISABLED");

        public static final Result DEFERED = new Result("DEFERED");
    }

    /**
     * Called by the state engine to determine whether a transition is enabled, defered, or disabled. The result is
     * interpreted as follows:
     * <ul>
     * <li>ENABLED if the transition is ready to proceed
     * <li>DISABLED if the transition is not ready to proceed
     * <li>DEFERED if the action associated with the transition is to be deferred. This means that the input will not be
     * acted upon, but rather it will be saved for later execution. Typically this is implemented using a CondVar wait,
     * and the blocked thread represents the defered input. The defered input is retried when the thread runs again.
     * </ul>
     * 
     * @param FSM
     *            fsm is the state machine causing this action.
     * @param Input
     *            in is the input that caused the transition.
     */
    public Result evaluate(FSM fsm, Input in);
}

// end of Action.java