source: CIVL/examples/pthread/bug1fix.cvl@ 77be3db

/*****************************************************************************
* SOURCE: This is a translation of a Pthread program from the Lawrence Livermore
* Computing Center POSIX Threads Programming Exercise at:
* https://computing.llnl.gov/tutorials/pthreads/exercise.html
* SUPERSOURCE: Adapted from example code in "Pthreads Programming", B. Nichols
*   et al. O'Reilly and Associates.
* FILE: bug1fix.cvl
* DESCRIPTION:
*       Solution for the bug1.cvl program.  The inc_count routine uses a
*   pthread_cond_broadcast() routine instead of the pthread_cond_signal()
*   routine.
* Command line execution:
* civl verify bug1fix.cvl
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

#define NUM_THREADS  6
#define TCOUNT 10
#define COUNT_LIMIT 12

int     count = 0;
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *inc_count(void *idp) 
{
  int j,i;
  double result=0.0;
  long my_id = (long)idp;
  for (i=0; i < TCOUNT; i++) {
    pthread_mutex_lock(&count_mutex);
    count++;

    /* 
    Check the value of count and signal waiting thread when condition is
    reached.  Note that this occurs while mutex is locked. 
    */
    if (count == COUNT_LIMIT) {
      pthread_cond_broadcast(&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);

    /* Do some work so threads can alternate on mutex lock */
    sleep(1);

    }
  pthread_exit(NULL);
}

void *watch_count(void *idp) 
{
  long my_id = (long)idp;

  printf("Starting watch_count(): thread %ld\n", my_id);

  /*
  Lock mutex and wait for signal.  Note that the pthread_cond_wait routine
  will automatically and atomically unlock mutex while it waits. 
  Also, note that if COUNT_LIMIT is reached before this routine is run by
  the waiting thread, the loop will be skipped to prevent pthread_cond_wait
  from never returning.
  */
  pthread_mutex_lock(&count_mutex);
    printf("***Before cond_wait: thread %ld\n", my_id);
    pthread_cond_wait(&count_threshold_cv, &count_mutex);
    printf("***Thread %ld Condition signal received.\n", my_id);
  pthread_mutex_unlock(&count_mutex);
  pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
int i, rc;
pthread_t threads[6];
pthread_attr_t attr;

/* 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[2], &attr, watch_count, (void *)2);
pthread_create(&threads[3], &attr, watch_count, (void *)3);
pthread_create(&threads[4], &attr, watch_count, (void *)4);
pthread_create(&threads[5], &attr, watch_count, (void *)5);
pthread_create(&threads[0], &attr, inc_count, (void *)0);
pthread_create(&threads[1], &attr, inc_count, (void *)1);

/* 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);

}