使用链表进行循环调度

Question

I'm trying to implement the Round Robin algorithm for a CPU Scheduler Simulator but using a linked list structure.

I've wrote this code but seems not working as it should be:

//Round Robin scheduling
void roundRobin(){

bubbleSortArrivalTime();

struct process *temp;
int totalTimeCnt=0;
int totalTime;
int quantum=4;
int i;

for(temp=proc; temp!=NULL; temp=temp->next){
totalTime+=temp->burstTime;

}

do{


for(i=1; i<LISTSIZE; i++){

if(i==1){
set_nth_process_burstTime(proc, i, get_nth_process_burstTime(proc,i)-quantum);

//set_nth_process_waitingTime(proc, i, get_nth_process_burstTime(proc,i-1)+get_nth_process_waitingTime(proc, i-1));

totalTime+=4;
}

else{
set_nth_process_burstTime(proc, i, get_nth_process_burstTime(proc,i)-quantum);
set_nth_process_waitingTime(proc, i, get_nth_process_burstTime(proc,i-1)+get_nth_process_waitingTime(proc, i-1));
totalTime+=4;
}

}


}while(totalTimeCnt!=0);


method="Method selected: Round Robin Scheduling";


}

The structure of my linked list is as follows:

    struct process{
    int burstTime,arrivalTime, priority,pname;
    float waitingTime, turnArroundTime;
    struct process *next;
}*proc=NULL;

where proc is defined as global.

I've implemented some get and set functions to access any element easily:

void set_nth_process_burstTime(struct process*header, int position, int value)
void set_nth_process_waitingTime(struct process *header, int position, float value)
int get_nth_process_waitingTime(struct process *header, int position)
int get_nth_process_priority(struct process *header,int position)
int get_nth_process_arrivalTime(struct process *header,int position)
int get_nth_process_burstTime(struct process *header,int position)

Could you please advice me on how to implement the Round Robin correctly? It is not giving the correct results.

Answer 1

round robin is very simple. in the main function, after all the initialization, setting of interrupts, etc, there is:

while(1)
{
    process_1();
    process_2();
    process_3();
    ...
}

Anything beyond that would be due to some special considerations for the specific project.

To implement a scheduler + dispatcher , with multiple desired execution intervals, priorities, condition states, aging, etc is a completely different architecture.

for round robin , the above while() loop is it.

For a realistic project, you will also need:

1. certain interrupt driven processes for timing and I/O,
2. handling of the watchdog timer
3. warm and cold boot modes
4. powerup BIT
5. continuous BIT
6. commanded BIT

Answer 2

#include<stdio.h> 

struct process {
char na[20];
int at, bt, ft, tat, rem;
float ntat;
} Q[5], temp;

void roundRobin() {
 int rr[20], q, x, k;
int f, r, n, i, j, tt = 0, qt, t, flag, wt = 0;
float awt = 0, antat = 0, atat = 0;

printf("Enter the no. of jobs:");
scanf("%d", &n);
for (r = 0; r < n; r++) {
    printf("Enter process name,arrival time and burst time:\n");
    scanf("%s%d%d", Q[r].na, &Q[r].at, &Q[r].bt);
}
printf("Enter quantum:\n");
scanf("%d", &qt);
for (i = 0; i < n; i++) {
    for (j = i + 1; j < n; j++) {
        if (Q[i].at > Q[j].at) {
            temp = Q[i];
            Q[i] = Q[j];
            Q[j] = temp;
        }
    }
}
for (i = 0; i < n; i++) {
    Q[i].rem = Q[i].bt;
    Q[i].ft = 0;
}
tt = 0;
q = 0;
rr[q] = 0;
do {
    for (j = 0; j < n; j++)
        if (tt >= Q[j].at) {
            x = 0;
            for (k = 0; k <= q; k++)
                if (rr[k] == j)
                    x++;
            if (x == 0) {
                q++;
                rr[q] = j;
            }
        }
    if (q == 0)
        i = 0;
    if (Q[i].rem == 0)
        i++;
    if (i > q)
        i = (i - 1) % q;
    if (i <= q) {
        if (Q[i].rem > 0) {
            if (Q[i].rem < qt) {
                tt += Q[i].rem;
                Q[i].rem = 0;
            } else {
                tt += qt;
                Q[i].rem -= qt;
            }
            Q[i].ft = tt;
        }
        i++;
    }
    flag = 0;
    for (j = 0; j < n; j++)
        if (Q[j].rem > 0)
            flag++;
} while (flag != 0);

printf("\n\n\t\tROUND ROBIN ALGORITHM");
printf("\n***************************");
printf("\nprocesses Arrival time burst time finish time tat wt ntat");
for (f = 0; f < n; f++) {
    wt = Q[f].ft - Q[f].bt - Q[f].at;
    Q[f].tat = Q[f].ft - Q[f].at;
    Q[f].ntat = (float) Q[f].tat / Q[f].bt;
    antat += Q[f].ntat;
    atat += Q[f].tat;
    awt += wt;
    printf("\n\t%s\t%d\t\t%d\t%d\t%d\t%d %f", Q[f].na, Q[f].at, Q[f].bt,
            Q[f].ft, Q[f].tat, wt, Q[f].ntat);
}
antat /= n;
atat /= n;
awt /= n;
printf("\nAverage tat is %f", atat);
printf("\nAverage normalised tat is %f", antat);
printf("\n average waiting time is %f", awt);
}