Class RRScheduler

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

class RRScheduler

extends Scheduler

A round-robin Scheduler for a CPU. It maintains a linked list of jobs. This scheduler is remarkably similar to the DiskScheduler.

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)

RRScheduler()

Method Summary

boolean	add(Job j) Add a new job wanting service.
void	printQueue() For debugging: print the queue of waiting jobs
private java.lang.String	queueString() For debugging.
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

RRScheduler

RRScheduler()

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. Return null if there is no such job.

Overrides:

remove in class Scheduler

Tags copied from 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

queueString

private java.lang.String queueString()

For debugging.

Returns:

a concise version of the queue of waiting jobs