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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