Subversion Repositories programming

/*******************************************************************************

 * SJFScheduler.java

 *

 * This file holds the implementation of the SJFScheduler class, which is a

 * Shortest Job First Scheduler, non-preemptive.

 *

 * 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.

 ******************************************************************************/

import java.util.Comparator;

import java.util.Vector;

import java.lang.ClassCastException;

/**

 * A Shortest Job First Scheduler

 *

 * @class CS431 Fall 2006

 * @author Ira W. Snyder (devel@irasnyder.com)

 */

public class SJFScheduler extends Scheduler

{

    /**

     * An SJFProcess is a Process with these additions:

     * 1) It has an add time associated with it

     */

    private class SJFProcess extends Process

    {

        /** The time to add this process to the run queue */

        public final int add_time;

        /**

         * Construct an instance of the SJFProcess class.

         *

         * @param name the name of this Process

         * @param timeslice this Process' burst time

         * @param add_time the time when this process will be added

         *                 to the run queue

         */

        public SJFProcess (String name, int timeslice, int add_time)

        {

            super(name, timeslice);

            this.add_time = add_time;

        }

    }

    /** Holds all Processes that will be added to the run queue after a delay */

    private Vector<SJFProcess> wait_queue;

    /**

     * Constructor for the Shortest Job First Scheduler.

     */

    public SJFScheduler ()

    {

        super ();

        this.wait_queue = new Vector<SJFProcess> ();

    }

    /**

     * Add a process to the wait queue, so that they can be pulled into the

     * run queue at the appropriate time.

     *

     * @param proc the Process to add

     * @param add_time the time when the Process is to be added

     */

    public void addProcess (Process proc, int add_time)

    {

        wait_queue.add (new SJFProcess (proc.name, proc.timeslice, add_time));

    }

    /**

     * Find the Process with the shortest timeslice in the run queue.

     *

     * @return the Process with the shortest timeslice

     */

    private Process findShortest ()

    {

        Process shortest = new Process ("fake", Integer.MAX_VALUE);

        for (Process p : run_queue)

            if (p.timeslice < shortest.timeslice)

                shortest = p;

        return shortest;

    }

    /**

     * Emulate a single time unit in a Shortest Job First scheduler.

     *

     * @return false if the scheduler is finished, true otherwise

     */

    protected boolean step ()

    {

        /* Leave if we are truly done */

        if (cur_proc == null && run_queue.isEmpty () && wait_queue.isEmpty ())

            return false;

        /* Create a clone of wait_queue. This is so we can delete things from

         * the actual wait_queue, while iterating over it */

        Vector<SJFProcess> wq_clone = (Vector<SJFProcess>)wait_queue.clone ();

        /* Pull anything that gets added at this time into run_queue */

        for (SJFProcess p : wq_clone)

            if (p.add_time == cur_time)

            {

                wait_queue.remove (p);

                run_queue.add (p);

            }

        /* If there is no process, then get one! */

        if (cur_proc == null)

            startProcess (findShortest ());

        /* If the current process is set to run, do so, return false */

        if (cur_proc.time_left > 0)

            scheduleCurrent ();

        else

            completeCurrent ();

        return true;

    }

}

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