CPSC–313 / Spring 2008 Machine Problem 2 / Step 3
Machine Problem 2: Simple Thread Scheduling
Total Machine Problem: 100 points
This Handout is for Step 3 of MP2
Due date: Check CSNET
Introduction
In Step 1 of this machine problem you implemented a simple task system that uses the system (or
the pthread library) scheduler for scheduling.
In Step 2 you added scheduling support to the task system.
In Step 3 we lay the foundation to extend the scheduling support to include preemptive round-
robin scheduling. The Round-Robin scheduler will be implemented as a class RRScheduler, which
is derived from class Scheduler. The class is defined as follows:
class RRScheduler : public Scheduler {
protected:
long time_quantum; /* in musec */
Timer * quantum_timer;
friend class EndOfQuantumTimer;
virtual void handle_end_of_quantum();
public:
RRScheduler(char _name[], long _quantum);
/* Instantiate a new scheduler. The quantum is given in musec. */
~RRScheduler();
/* Don’t need to implement for now... */
/* -- START SCHEDULING THE TASKS */
virtual int Kick_Off();
/* -- SCHEDULING OPERATIONS */
virtual int Start(Schedulable * _task);
/* Start scheduling this task. See Scheduler::Start(). */
virtual int Yield();
/* The calling task gives up the CPU.
Basically the same as Scheduler::Yield(), but we need to
take care of the quantum timer first. */
virtual int Resume(Schedulable * _task);
/* Resume the given _task. */
};
The quantum management in the scheduler is handled by an object of class EndOfQuantumTimer,
which is derived from class Timer. The forced context switch is called from within the event handler
of the end-of-quantum event handler.
class EndOfQuantumTimer : public Timer {
private:
RRScheduler * sched;
public:
EndOfQuantumTimer(RRScheduler * _sched) {
sched = _sched;
}
virtual void event_handler() {
printf("END-OF-QUANTUM TIMER: ");
Page 1
