/******************************************************************************* FILE: condvar1.c* 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.* SOURCE: Adapted from example code in "Pthreads Programming", B. Nichols*   et al. O'Reilly and Associates. * LAST REVISED: 04/05/05  Blaise Barney******************************************************************************/#include <pthread.h>#include <stdio.h>#include <stdlib.h>#define NUM_THREADS  3#define TCOUNT 10#define COUNT_LIMIT 12int     count = 0;int     thread_ids[3] = {0,1,2};pthread_mutex_t count_mutex;pthread_cond_t count_threshold_cv;void *inc_count(void *idp) {  int j,i;  double result=0.0;  int *my_id = 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_signal(&count_threshold_cv);      printf("inc_count(): thread %d, count = %d  Threshold reached.\n",              *my_id, count);      }    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 */    for (j=0; j < 1000; j++)      result = result + (double)random();    }  pthread_exit(NULL);}void *watch_count(void *idp) {  int *my_id = idp;  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) {    pthread_cond_wait(&count_threshold_cv, &count_mutex);    printf("watch_count(): thread %d 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[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, inc_count, (void *)&thread_ids[0]);  pthread_create(&threads[1], &attr, inc_count, (void *)&thread_ids[1]);  pthread_create(&threads[2], &attr, watch_count, (void *)&thread_ids[2]);  /* 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);}