Class DiskScheduler

java.lang.Object
  |
  +--Scheduler
        |
        +--DiskScheduler

class DiskScheduler

extends Scheduler

A FCFS scheduler for the disk. It maintains a simple queue of jobs.

Field Summary

private Job	head The head of a queue of jobs awaiting service.
private Job	tail

Fields inherited from class Scheduler

lastChanged, lenSum, maxLen, MAXQUEUE, qlen, queueHist

Constructor Summary

(package private)

DiskScheduler()

Method Summary

boolean	add(Job j) Add a new job wanting service.
void	printQueue() For debugging: print the queue of waiting jobs
Job	remove() Retrieve (and remove) the next job to be served.
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 Scheduler

printStats, queueChanged

Methods inherited from class java.lang.Object

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

Field Detail

head

private Job head

The head of a queue of jobs awaiting service. If the queue is empty, head = null and the value of tail is undefined.

tail

private Job tail

Constructor Detail

DiskScheduler

DiskScheduler()

Method Detail

add

public boolean add(Job j)

Add a new job wanting service.

Overrides:

add in class Scheduler

Parameters:

j - the job to serve

Returns:

false (this scheduler never preempts)

remove

public Job remove()

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

Overrides:

remove in class Scheduler

Returns:

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

reschedule

public boolean reschedule(Job j)

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

Overrides:

reschedule in class Scheduler

Parameters:

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

Returns:

true if the scheduler wants to preempt the current job.

printQueue

public void printQueue()

For debugging: print the queue of waiting jobs

Overrides:

printQueue in class Scheduler