source: CIVL/examples/pthread/condvar.cvl@ 761eb6f

/*****************************************************************************
* 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: condvar.cvl
* DESCRIPTION:
*   Example code for using Pthreads condition variables.  The main thread
*   creates three threads.  Two of those threads increment a "count" variable,
*   while the third thread watches the value of "count".  When "count" 
*   reaches a predefined limit, the waiting thread is signaled by one of the
*   incrementing threads. The waiting thread "awakens" and then modifies
*   count. The program continues until the incrementing threads reach
*   TCOUNT. The main program prints the final value of count.
* Command line execution:
* civl verify -inputNUM_THREADS=3 -inputTCOUNT=10 -inputCOUNT_LIMIT=12 condvar.cvl
******************************************************************************/
#include "pthread.cvh"
#include <civlc.h>
#include <stdio.h>
#include <stdlib.h>

$input int NUM_THREADS;
$input int TCOUNT;
$input int COUNT_LIMIT;

int count = 0;
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *inc_count(void *t) 
{
  int i;
  long my_id = (long)*t;

  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) {
      printf("inc_count(): thread %d, count = %d  Threshold reached. ",
             my_id, count);
      pthread_cond_signal(&count_threshold_cv);
      printf("Just sent signal.\n");
      }
    printf("inc_count(): thread %d, 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 *t) 
{
  long my_id = (long)*t;

  printf("Starting watch_count(): thread %d\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);
  while (count < COUNT_LIMIT) {
    printf("watch_count(): thread %d Count= %d. Going into wait...\n", my_id,count);
    pthread_cond_wait(&count_threshold_cv, &count_mutex);
    printf("watch_count(): thread %d Condition signal received. Count= %d\n", my_id,count);
    printf("watch_count(): thread %d Updating the value of count...\n", my_id,count);
    count += 125;
    printf("watch_count(): thread %d count now = %d.\n", my_id, count);
    }
  printf("watch_count(): thread %d Unlocking mutex.\n", my_id);
  pthread_mutex_unlock(&count_mutex);
  pthread_exit(NULL);
}

int main(void)
{
  int i, rc; 
  long t1=1, t2=2, t3=3;
  pthread_t threads[3];
  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[0], &attr, watch_count, (void *)&t1);
  pthread_create(&threads[1], &attr, inc_count, (void *)&t2);
  pthread_create(&threads[2], &attr, inc_count, (void *)&t3);

  /* Wait for all threads to complete */
  for (i = 0; i < NUM_THREADS; i++) {
    pthread_join(threads[i], NULL);
  }
  printf ("Main(): Waited and joined with %d threads. Final value of count = %d. Done.\n", 
          NUM_THREADS, count);

  /* Clean up and exit */
  pthread_attr_destroy(&attr);
  pthread_mutex_destroy(&count_mutex);
  pthread_cond_destroy(&count_threshold_cv);
  pthread_exit (NULL);
  return 0;
}