test_pthread_condition_variable.cpp

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <emscripten/emscripten.h>
#include <emscripten/threading.h>

#define NUM_THREADS  3
#define TCOUNT 10
#define COUNT_LIMIT 12

int     count = 0;
int     thread_ids[3] = {0,1,2};
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) {
      pthread_cond_signal(&count_threshold_cv);
 //     printf("inc_count(): thread %ld, count = %d  Threshold reached.\n", 
 //            my_id, count);
      EM_ASM_INT( { Module['print']('inc_count(): thread ' + $0 + ', count = ' + $1 + ', Threshold reached.'); }, my_id, count);
      }
//    printf("inc_count(): thread %ld, count = %d, unlocking mutex\n", 
//	   my_id, count);
    EM_ASM_INT( { Module['print']('inc_count(): thread ' + $0 + ', count = ' + $1 + ', unlocking mutex.'); }, 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 %ld\n", my_id);
  EM_ASM_INT( { Module['print']('Starting watch_count(): thread ' + $0); }, 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) {
    pthread_cond_wait(&count_threshold_cv, &count_mutex);
//    printf("watch_count(): thread %ld Condition signal received.\n", my_id);
    EM_ASM_INT( { Module['print']('watch_count(): thread ' + $0 + ' Condition signal received.'); }, my_id);
    count += 125;
//    printf("watch_count(): thread %ld count now = %d.\n", my_id, count);
    EM_ASM_INT( { Module['print']('watch_count(): thread ' + $0 + ', count now = ' + $1); }, my_id, count);
    }
  pthread_mutex_unlock(&count_mutex);
  pthread_exit(NULL);
}

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

  if (emscripten_has_threading_support())
  {
    /* 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);
#ifdef REPORT_RESULT
  int result = 0;
  REPORT_RESULT();
#endif
  pthread_exit(NULL);
}