Crtical Sections

mohd2012 · 05-07-2012, 01:50 AM

Hello every one

I am new here I need your help to understand how we use The Gnome library (glib).. to solve critical section problem..

How can I a Adapt the following C program from class in such a way that it uses the test and set() functionto to protect the critical sections in the two calculating threads.

Test and set function:

gboolean test_and_set(int *target) {
return !g_atomic_int_compare_and_exchange(target,0,1);
}

C programme :

Code:

#include <pthread.h>
#include <stdio.h>
#include <glib.h>
double sum;
void* runner1(void *param);
void* runner2(void *param);
int main(int argc, char *argv[]) {
pthread_t tid1;
pthread_t tid2;
pthread_attr_t attr;

if (argc != 2) {
  fprintf(stderr,"usage: program <positive integer>\n");
  return -1;
}
if (atoi(argv[1]) < 0) {
  fprintf(stderr,"%d must be >= 0\n",atoi(argv[1]));
  return -1;
}

sum = 0;

pthread_attr_init(&attr);
pthread_create(&tid1,&attr,runner1,argv[1]);
pthread_create(&tid2,&attr,runner2,argv[1]);
pthread_join(tid1,NULL);
pthread_join(tid2,NULL);

printf("sum = %f\n",sum);
}
void* runner1(void *param) {
int i;
int N2 = atoi(param) / 2;
for (i=1;i<=N2;++i) {
  sum += i;
}

pthread_exit(0);
}
void* runner2(void *param) {
int j;
int N = atoi(param);
int j1 = N / 2 + 1;
for (j=j1;j<=N;++j) {
  sum += j;
}

pthread_exit(0);
}

sundialsvcs · 05-07-2012, 09:08 AM

Well, obviously I don't want to "give you the answer to a homework problem"

but I'll be happy to try turning some lights on.

A "test and set" instruction (by any other name...) is an atomic machine-instruction that examines the value of a memory location and optionally sets its value in a single, uninterruptible operation. It eliminates the race condition that would otherwise occur in a sequence such as if (a=1) a++;.

In order to solve this assignment, you need to now research and decide how to use this capability to create "turnstiles and bathroom stalls" in your program. Instead of simply asking a stranger to write your answer for you (which, BTW, your teacher will most certainly see because you can bet that he/she also has an account here ...), surf for examples and for discussions of how they work. Then you will learn, and forever after you too will know.

mohd2012 · 05-08-2012, 05:47 AM

This my try after search to understand how test and ste funcation use:

i think i have some thing wrong withine the while loop ? any help?

Code:

#include <pthread.h>
#include <stdio.h>
#include <gilb.h>


double sum; 

void* runner1(void *param);
void* runner2(void *param);




int main(int argc, char *argv[]) {

	pthread_t tid1;
	pthread_t tid2;
	pthread_attr_t attr;
	
	if (argc != 2) {
		fprintf(stderr,"usage: program <positive integer>\n");
		return -1;
	}
	if (atoi(argv[1]) < 0) {
		fprintf(stderr,"%d must be >= 0\n",atoi(argv[1]));
		return -1;
	}	
	
	sum = 0;
	
	pthread_attr_init(&attr);
	//pthread_create(&tid1,&attr,runner1,argv[1]);
	//pthread_create(&tid2,&attr,runner2,argv[1]);
	//pthread_join(tid1,NULL);
	//pthread_join(tid2,NULL);
	
	printf("sum = %f\n",sum);



Int lock = 1;
do {
	while (test_and_set(&lock));
				pthread_create(&tid1,&attr,runner1,argv[1]);
				pthread_join(tid1,NULL);
	lock = FALSE;
				pthread_create(&tid2,&attr,runner2,argv[1]);
			        pthread_join(tid2,NULL);
	

		} while (TRUE);	

            printf("sum = %f\n",sum);

}


void* runner1(void *param) {

	int i;
	int N2 = atoi(param) / 2;
	for (i=1;i<=N2;++i) {
		sum += i;
	}
	
	pthread_exit(0);
}
void* runner2(void *param) {

	int j;
	int N = atoi(param);
	int j1 = N / 2 + 1;
	for (j=j1;j<=N;++j) {
		sum += j;
	}
	
	pthread_exit(0);
}

gboolean test_and_set(int *target) {
return !g_atomic_int_compare_and_exchange(target,0,1);
}