Thread scheduling Round Robin / scheduling dispatch
- by MRP
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#define NUM_THREADS 4
#define COUNT_LIMIT 13
int done = 0;
int count = 0;
int quantum = 2;
int thread_ids[4] = {0,1,2,3};
int thread_runtime[4] = {0,5,4,7};
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;
void * inc_count(void * arg);
static sem_t count_sem;
int quit = 0;
///////// Inc_Count////////////////
void *inc_count(void *t)
{
long my_id = (long)t;
int i;
sem_wait(&count_sem); /////////////CRIT SECTION//////////////////////////////////
printf("run_thread = %d\n",my_id);
printf("%d \n",thread_runtime[my_id]);
for( i=0; i < thread_runtime[my_id];i++)
{
printf("runtime= %d\n",thread_runtime[my_id]);
pthread_mutex_lock(&count_mutex);
count++;
if (count == COUNT_LIMIT) {
pthread_cond_signal(&count_threshold_cv);
printf("inc_count(): thread %ld, count = %d Threshold reached.\n", my_id,
count);
}
printf("inc_count(): thread %ld, count = %d, unlocking mutex\n",my_id, count);
pthread_mutex_unlock(&count_mutex);
sleep(1) ;
}//End For
sem_post(&count_sem); // Next Thread Enters Crit Section
pthread_exit(NULL);
}
/////////// Count_Watch ////////////////
void *watch_count(void *t)
{
long my_id = (long)t;
printf("Starting watch_count(): thread %ld\n", my_id);
pthread_mutex_lock(&count_mutex);
if (count<COUNT_LIMIT) {
pthread_cond_wait(&count_threshold_cv, &count_mutex);
printf("watch_count(): thread %ld Condition signal received.\n", my_id);
printf("watch_count(): thread %ld count now = %d.\n", my_id, count);
}
pthread_mutex_unlock(&count_mutex);
pthread_exit(NULL);
}
////////////////// Main ////////////////
int main (int argc, char *argv[])
{
int i;
long t1=0, t2=1, t3=2, t4=3;
pthread_t threads[4];
pthread_attr_t attr;
sem_init(&count_sem, 0, 1);
/* Initialize mutex and condition variable objects */
pthread_mutex_init(&count_mutex, NULL);
pthread_cond_init (&count_threshold_cv, NULL);
/* For portability, explicitly create threads in a joinable state */
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&threads[0], &attr, watch_count, (void *)t1);
pthread_create(&threads[1], &attr, inc_count, (void *)t2);
pthread_create(&threads[2], &attr, inc_count, (void *)t3);
pthread_create(&threads[3], &attr, inc_count, (void *)t4);
/* Wait for all threads to complete */
for (i=0; i<NUM_THREADS; i++) {
pthread_join(threads[i], NULL);
}
printf ("Main(): Waited on %d threads. Done.\n", NUM_THREADS);
/* Clean up and exit */
pthread_attr_destroy(&attr);
pthread_mutex_destroy(&count_mutex);
pthread_cond_destroy(&count_threshold_cv);
pthread_exit(NULL);
}
I am trying to learn thread scheduling, there is a lot of technical coding that I don't know. I do know in theory how it should work, but having trouble getting started in code...
I know, at least I think, this program is not real time and its not meant to be.
Some how I need to create a scheduler dispatch to control the threads in the order they should run... RR FCFS SJF ect.
Right now I don't have a dispatcher. What I do have is semaphores/ mutex to control the threads.
This code does run FCFS... and I have been trying to use semaphores to create a RR.. but having a lot of trouble. I believe it would be easier to create a dispatcher but I dont know how.
I need help, I am not looking for answers just direction.. some sample code will help to understand a bit more.
Thank you.
