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/*******************************************************************************
 * RRScheduler.java
 *
 * Implementation of a Round-Robin Scheduler for CS431 Project #1.
 *
 * Copyright (c) 2006, Ira W. Snyder (devel@irasnyder.com)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 ******************************************************************************/

/**
 * A Round-Robin Scheduler.
 *
 * @class CS431 Fall 2006
 * @author Ira W. Snyder (devel@irasnyder.com)
 */
public class RRScheduler extends Scheduler
{
    /** the interval at which to switch processes */
    protected final int interval;

    /** the amount of time that the current process has been running */
    protected int cur_proc_runtime = 0;

    /**
     * Constructor for the Round Robin Scheduler class.
     */
    public RRScheduler (int interval)
    {
        super ();
        this.interval = interval;
    }

    /**
     * Emulates a single time unit in a Round Robin Scheduler.
     *
     * @return false if there is nothing left to do, true otherwise
     */
    protected boolean step ()
    {
        /* Stop if we have nothing left to do */
        if (cur_proc == null && run_queue.isEmpty ())
            return false;

        /* Get a new process if we need to */
        if (cur_proc == null)
        {
            startProcess (run_queue.firstElement ());
            cur_proc_runtime = 0;
        }

        /* Run the process */
        if (cur_proc_runtime < interval)
        {
            if (cur_proc.time_left > 0)
            {
                scheduleCurrent ();
                cur_proc_runtime++;
            }
            else
                completeCurrent ();
        }
        else
        {
            if (cur_proc.time_left > 0)
                expireCurrent ();
            else
                completeCurrent ();
        }

        return true;
    }
}

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