CodeProject
This program is general and considers the case when no programs may be running also.
/* AUTHOR : VINAY CHOUDHARY
DATE : 20-11-2010
TITLE : ROUND ROBIN SCHEDULING ALGORITHM
COMPANY :
TIME :
*/
#include<stdio.h>
#include<stdlib.h>
#define NUM_PRC 5 //number of process
#define TIME_QUANTUM 3 //time quantum
#define CONTEXT_SWT 1 //context switch time between process, set 0 if not to be included
int ARR[NUM_PRC]; //arrival times of processes
int BRS[NUM_PRC]; //burst times of processes
int STR[NUM_PRC]; //start times
int FIN[NUM_PRC]; //finish times
int WAT[NUM_PRC]; //waiting times
int TRN[NUM_PRC]; //turn around times
void get_times();
void RR();
void calc(int *tt, int *tw,float *at,float *aw);
void print(int *tt, int *tw,float *at,float *aw);
int main()
{
int TT,TW; //total wait & turnaround times
float avg_wat,avg_trn; //average wait & turnaround times
get_times();
RR();
calc(&TT,&TW,&avg_wat,&avg_trn);
print(&TT,&TW,&avg_wat,&avg_trn);
printf("\n\n***** END OF RR *****\n\n");
return 0;
}
void get_times()
{
int i;
printf("\n***** GETTING ARRIVAL & BURST TIMES *****\n");
for(i=0;i<NUM_PRC;i++)
{
STR[i] = -1; //set this to -1 to mark it as not started
printf("Enter arrival & burst time for process[%d] : ",i+1);
scanf("%d%d",&ARR[i],&BRS[i]);
}
}
void RR()
{
int exc_time=0; //initially execution time is 0
int remain=NUM_PRC; //unterminated processes
int t_BRS[NUM_PRC]; //temporary BRS ARRAY
int i;
int prc_executed;
int started=0; //any process runs scheduling started
for(i=0;i<NUM_PRC;i++)
t_BRS[i] = BRS[i];
while(remain)
{
prc_executed = 0;
for(i=0;i<NUM_PRC;i++)
{
//If process has arrived at this time
//and has burst time remaining then run it.
if(t_BRS[i] > 0 && ARR[i] <= exc_time)
{
//If no process has started then no need for CONTEXT_SWT.
//When schedular is idle started is set to 0, since it is now ruuning set stated to 1.
//If some process was ruuninng in previous time quantum add CONTEXT_SWT.
if(started == 0)
started = 1;
else
exc_time = exc_time + CONTEXT_SWT;
//If first run
//then current exc_time is its start time.
if(STR[i] == -1)
STR[i] = exc_time;
//Decrease TIME_QUANTUM from BRST time because process has run for this time.
t_BRS[i] = t_BRS[i] - TIME_QUANTUM;
//Increase exc_time by TIME_QUANTUM.
exc_time = exc_time + TIME_QUANTUM;
//Mark that a process was executed, used to increment exc_time
//by 1 unit if no process was ready to run
prc_executed = 1;
if(t_BRS[i] <= 0)
{ //If process completes.
exc_time = exc_time + t_BRS[i];
//If t_BRS[i] is -ve means it ran for less than TIME_QUANTUM and extra time must be subtracted.
//This extra time is in t_BRS[i],e.g, if it had to runs for 1s and TIME_QUANTUM is 3s then
//it should only run for 1s. so after t_BRS[i] = t_BRS[i] - TIME_QUANTUM, t_BRS[i] is -2, meanining
//2s must be subtracted from exc_time
FIN[i] = exc_time; //current exc_time is finish time then
remain--; //decrease number of remaining process
}
}
}
if(prc_executed == 0)
{
//If no process executed increment execution time by 1 unit, this is used in case there is no process ready to run.
started = 0;
//since no process was executed set schedular to idle so that there is no contect switch when a process arrives
exc_time++;
}
}
}
void calc(int *tt, int *tw,float *at,float *aw)
{
int i;
*tw = *tt = 0;
for(i=0;i<NUM_PRC;i++)
{
TRN[i] = FIN[i] - ARR[i]; //turnaround time = finish time - submission time
WAT[i] = TRN[i] - BRS[i]; //wait time = finish time - submission time - burst time
//or wait time = turnaround time - burst time, this is time spent in ready queue
*tw += WAT[i];
*tt += TRN[i]; //total wait & turn around times
}
*at = (float)*tt/NUM_PRC;
*aw = (float)*tw/NUM_PRC; //average wait & turn around times
}
void print(int *tt, int *tw,float *at,float *aw)
{
int i;
printf("\n\nPID ARR BRS STR FIN WAT TRN");
printf("\n---------------------------");
for(i=0;i<NUM_PRC;i++)
printf("\n%3d %3d %3d %3d %3d %3d %3d",i+1,ARR[i],BRS[i],STR[i],FIN[i],WAT[i],TRN[i]);
printf("\n---------------------------\n");
printf("\nTOTAL TURNAROUND TIME : %d\tAVERAGE TURNAROUND TIME : %.2f",*tt,*at);
printf("\nTOTAL WAITING TIME : %d\tAVERAGE WAITING TIME : %.2f",*tw,*aw);
}
