I am working on a Round Robin scheduler with time quanta of 4 for an OS class currently. The only file I am editing is the scheduler file. I believe I implemented the linked list correctly, but it seems as though I am adding processes back to the list incorrectly(aka my round robin implementation is wrong). When the simulation is run, It executes each process for 4 time units but doesnt seem to add them back correctly. Only the last process executes fully. I feel like this should be handled correctly when I look at the simulation file, yet it is not. Any input or noticed problems would be helpful even if it is not a full fix! Thank you.

//HEADER FILE_ FOR SCHEDULER-----------------------------

#ifndef _schedule_h_ #define _schedule_h_

typedef struct { int pid; int priority; } PCB;

void init(); int addProcess(PCB* process);

PCB* nextProcess(int *time); int hasProcess();

#endif

//----------------SCHEDULER FILE----------------------

#include "schedule.h"

#include

#include

/**

* Function to initialize any global variables for the scheduler.

*/

struct node{

PCB* proc;

struct node* next;

};

struct node* root;

struct node* cur;

void init(){

root=NULL;

cur = root;

}

/**

* Function to add a process to the scheduler

* @Param process - Pointer to the process control block for the process that

* needs to be scheduled. PCB is defined in the header.

* @return true/false response for if the addition was successful

*/

int addProcess(PCB* process){

if(root==NULL){

root = (struct node*) malloc( sizeof(struct node));

cur = root;

}

else{

cur->next = (struct node*) malloc( sizeof(struct node));

cur = cur->next;

}

cur->proc = process;

return 0;

}

/**

* Function to get the next process from the scheduler

* @Param time - pass by reference variable to store the quanta of time

* the scheduled process should run for

* @Return returns pointer to process control block that needs to be executed

* returns NULL if there is no process to be scheduled.

*/

PCB* nextProcess(int *time){

cur=root;

//if(!(cur->proc->pid<0))

*time=4;

if(cur!=NULL){

PCB* temp_proc;

temp_proc=cur->proc;

cur=root;

if(root->next!=NULL)

root=root->next;

else

root=NULL;

free(cur);

return temp_proc;

}

else

return NULL;

}

/**

* Function that returns a boolean 1 True/0 False based on if there are any

* processes still scheduled

* @Return 1 if there are processes still scheduled 0 if there are no more

* scheduled processes

*/

int hasProcess(){

if(root==NULL)

return 0;

else

return 1;

}

//------------------SIMULATION FILE (CANNOT EDIT) -----------------------------

#include #include #include #include #include #include #include #include

#include "schedule.h"

// // main - The simulator's main routine // int main(int argc, char **argv){ int processes[10]; init(); int i; for(i=0;i<10;i++){ processes[i]=100; printf("Scheduled Process: %d ", i); PCB* proc = (PCB *) malloc(sizeof(PCB)); proc->pid = i; proc->priority=0; addProcess(proc); }

PCB* process = NULL; int time = 0; while(hasProcess()){ process = nextProcess(&time); if(!process){ printf("NULL Process, something went wrong in your code. "); exit(1); } for(;time>0;time--){ printf("Process %d executed ", process->pid); processes[process->pid]--; if(processes[process->pid]<0){ printf("Process %d Finished ", process->pid); break; } } if(processes[process->pid]>=0){ addProcess(process); } }

exit(0); //control never reaches here }