Documentation about a Code ( Threads)

[koxp]

I have a code but i dont understand it. Can someone explain me what happens in the code?

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <math.h>

int total = 0;
int activ = 0;

struct thr_parameter {

int start;
int end;
int thr_num;
};

void *Sector(void *arg)
{
while (activ != 0) {
printf("-> %d\n", total);
usleep(500000);
}
}
void *Thread_main(void *arg)
{
int i, j, k;
int prim;
int num = 0;
struct thr_parameter *p = arg;

activ++;
printf("Worker %d: Ready for Service\n", p->thr_num);
printf("Worker %d: ", p->thr_num);
printf("Starting calculation from %d to %d\n", p->start, p->end);

for (i = p->start; i <= p->end; i++) {
if (i == 1)
continue;
else if (i == 2 || i == 3)
prim = 1;
else {
prim = 1;
k = sqrt(i);
for (j = 2; j <= k; j++) {
if (i % j == 0) {
prim = 0;
break;
} }
}
if (prim) {
total++;
num++;
}
}
printf("Worker %d: Found %d Primes\n", p->thr_num, num);
activ--;
}

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

int threads = 0;
int l = 0;
int i = 1;
int sektor1 = 1;
int sektor2 = 0;
int maximum;
int j;
double diff;

struct thr_parameter *t_param;
struct timespec start, finish;

pthread_t *t;
pthread_t sector;

clock_gettime(CLOCK_MONOTONIC, &start);

while ((j = getopt(argc, argv, "N:t:")) != -1) {
switch (j) {
case 'N':
maximum = atoi(optarg);
break;
case 't':
threads = atoi(optarg);
break;
default:
break;
}
}

if (maximum < 2 || threads < 1)
exit(EXIT_FAILURE);


l = maximum / threads;

if (maximum % threads)
l++;

t = malloc(threads * sizeof(*t));

for (i = 0; i < threads; i++) {
sektor2 = sektor1 + l - 1;
if (sektor2 > maximum)
sektor2 = maximum;

t_param = malloc(sizeof(*t_param));
t_param->thr_num = i;
t_param->start = sektor1;
t_param->end = sektor2;

if (pthread_create(&t[i], NULL, Thread_main, (void *)t_param)) {
perror("ERROR");
exit(EXIT_FAILURE);
}
sektor1 = sektor2 + 1;
}

if (pthread_create(&sector, NULL, Sector, NULL)) {
perror("ERROR");
exit(EXIT_FAILURE);
}

if (pthread_join(sector, NULL)) {
perror("ERROR");
exit(EXIT_FAILURE);
}

for (i = 0; i < threads; i++) {
if (pthread_join(t[i], NULL)) {
perror("ERROR");
exit(EXIT_FAILURE);
}
}

printf("Total Prime Count: %d\n", total);

clock_gettime(CLOCK_MONOTONIC, &finish);

diff = (finish.tv_sec - start.tv_sec);
diff += (finish.tv_nsec - start.tv_nsec)/1000000000.0;

printf("RunTime: %f\n", diff);

free(t_param);
free(t);

return 0;
}

[keskiverto]

First, code is much easier to read, when it is posted within code tags and is indented too. See http://www.cplusplus.com/articles/jEywvCM9/


Which features in this program you are not familiar with?

[dhayden]

It appears to count prime numbers up to some limit called maximum. It uses multiple threads to do it. There are two command line arguments: -N lets you specify the maximum prime. -T lets you specify how many threads to use. Try running it with these command line options. It should help you figure out how it works:

-N 100000 -T 1
-N 100000 -T 2
-N 100000 -T 4
-N 500000 -T 4