#include <signal.h>
#include <unistd.h>
#include <semaphore.h>
#include <pthread.h>

sem_t thread_sem1;
sem_t thread_sem2;

void * thread_function1(void *arg);
void * thread_function2(void *arg);

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

  int i = 1;
  int j = 2;
  pthread_t thread2;
  
  sem_init(&thread_sem1, 0, 1);
  sem_init(&thread_sem2, 0, 0);

  pthread_create(&thread2, NULL, thread_function2, (void *)&j);
  thread_function1((void *)&i);

  return(0);
}

void * thread_function1(void *arg) {
  while(1) {
    sem_wait(&thread_sem1);
    printf("Thread %d running\n", *(int *)arg); 
    sem_post(&thread_sem2);
  }
}

void * thread_function2(void *arg) {
  while(1) {
    sem_wait(&thread_sem2);
    printf("Thread %d running\n", *(int *)arg); 
    sem_post(&thread_sem1);
  }
}