Class Scheduler

java.lang.Object
  |
  +--Scheduler

Direct Known Subclasses:

DiskScheduler, RRScheduler

abstract class Scheduler

extends java.lang.Object

A Scheduler schedules jobs seeking service from a Device. The class Scheduler itself is "abstract", meaning that there are no instance of Scheduler, only of its subclasses. This simulation has two Schedulers: DiskScheduler for scheduling the disk and RRScheduler for scheduling the CPU. The base class takes care of maintaining statistics on queue lengths. The subclasses do all the actual work.

See Also:

DiskScheduler, RRScheduler

Field Summary

private int	lastChanged The last time the queue length changed
private int	lenSum The time integral of queue length
private int	maxLen The maximum queue length
private static int	MAXQUEUE The max queue length we tally in the histogram
private int	qlen The current queue length
private int[]	queueHist The amount of time the queue had a given length

Constructor Summary

(package private)

Scheduler()

Method Summary

abstract boolean	add(Job j) Add a new job wanting service.
abstract void	printQueue() For debugging: print the queue of waiting jobs
void	printStats() Print statistics about the history of this queue.
protected void	queueChanged(int amount) This method should be called by a subclass whenever the queue length changes.
abstract Job	remove() Retrieve (and remove) the next job to be served.
abstract boolean	reschedule(Job j) This method is called when there is a clock interrupt, and just after a job changes state.

Methods inherited from class java.lang.Object

, clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, toString, wait, wait, wait

Field Detail

MAXQUEUE

private static final int MAXQUEUE

The max queue length we tally in the histogram

qlen

private int qlen

The current queue length

lastChanged

private int lastChanged

The last time the queue length changed

maxLen

private int maxLen

The maximum queue length

lenSum

private int lenSum

The time integral of queue length

queueHist

private int[] queueHist

The amount of time the queue had a given length

Constructor Detail

Scheduler

Scheduler()

Method Detail

add

public abstract boolean add(Job j)

Add a new job wanting service.

Parameters:

j - the job to serve

Returns:

true if this scheduler would like to preempt the current job.

remove

public abstract Job remove()

Retrieve (and remove) the next job to be served.

Returns:

the next job (null if there is no such job).

reschedule

public abstract boolean reschedule(Job j)

This method is called when there is a clock interrupt, and just after a job changes state.

Parameters:

j - the job currently being serviced by the corresponding device.

Returns:

true if the scheduler wants to preempt the current job.

printQueue

public abstract void printQueue()

For debugging: print the queue of waiting jobs

queueChanged

protected void queueChanged(int amount)

This method should be called by a subclass whenever the queue length changes.

printStats

public void printStats()

Print statistics about the history of this queue.