Class RRScheduler

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

public 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.

Constructor Summary

RRScheduler()

Method Summary

boolean	add(Job newJob, Job currentJob) 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 decides whether to preempt the current job.
java.lang.String	toString() For debugging: a concise version of the queue

Methods inherited from class Scheduler

endBurst, printStats, queueChanged

Methods inherited from class java.lang.Object

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

Constructor Detail

RRScheduler

public RRScheduler()

Method Detail

add

public boolean add(Job newJob,
                   Job currentJob)

Add a new job wanting service. For RR, it simply goes to the end of the queue.

Overrides:

add in class Scheduler

Parameters:

newJob - the job newly awaiting service for the device.

currentJob - the job currently using the device, if any (ignored)

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 decides whether to preempt the current job. For RR scheduling it returns true if the queue is non-empty and false otherwise (if nobody is waiting, the current job might as well continue).

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

toString

public java.lang.String toString()

For debugging: a concise version of the queue

Overrides:

toString in class java.lang.Object

Returns:

a concise version of the queue of waiting jobs