本文共 4535 字，大约阅读时间需要 15 分钟。

转自https://computing.llnl.gov/tutorials/pthreads/

#include 
   
    #include 
    
     #include 
     
      #include 
      
       #define NUM_THREADS  3#define TCOUNT 10#define COUNT_LIMIT 12int     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 %ld, count = %d  Threshold reached. ",             my_id, count);      pthread_cond_signal(&count_threshold_cv);      printf("Just sent signal.\n");      }    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 *t){
     long my_id = (long)t;  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.  ！！！pthread_cond_wait进入等待时会自动解锁mutex  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.  ！！!如果while循环条件跳出，会提前结束等待状态  */  pthread_mutex_lock(&count_mutex);  while (count < COUNT_LIMIT) {
       printf("watch_count(): thread %ld Count= %d. Going into wait...\n", my_id,count);    pthread_cond_wait(&count_threshold_cv, &count_mutex);    printf("watch_count(): thread %ld Condition signal received. Count= %d\n", my_id,count);    }  printf("watch_count(): thread %ld Updating the value of count...\n", my_id);  count += 125;  printf("watch_count(): thread %ld count now = %d.\n", my_id, count);  printf("watch_count(): thread %ld Unlocking mutex.\n", my_id);  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);  /* 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);}
      
     
    
   

输出

inc_count(): thread 3, count = 1, unlocking mutexinc_count(): thread 2, count = 2, unlocking mutexStarting watch_count(): thread 1watch_count(): thread 1 Count= 2. Going into wait...inc_count(): thread 3, count = 3, unlocking mutexinc_count(): thread 2, count = 4, unlocking mutexinc_count(): thread 3, count = 5, unlocking mutexinc_count(): thread 2, count = 6, unlocking mutexinc_count(): thread 3, count = 7, unlocking mutexinc_count(): thread 2, count = 8, unlocking mutexinc_count(): thread 3, count = 9, unlocking mutexinc_count(): thread 2, count = 10, unlocking mutexinc_count(): thread 3, count = 11, unlocking mutexinc_count(): thread 2, count = 12  Threshold reached. Just sent signal.inc_count(): thread 2, count = 12, unlocking mutexwatch_count(): thread 1 Condition signal received. Count= 12watch_count(): thread 1 Updating the value of count...watch_count(): thread 1 count now = 137.watch_count(): thread 1 Unlocking mutex.inc_count(): thread 3, count = 138, unlocking mutexinc_count(): thread 2, count = 139, unlocking mutexinc_count(): thread 3, count = 140, unlocking mutexinc_count(): thread 2, count = 141, unlocking mutexinc_count(): thread 3, count = 142, unlocking mutexinc_count(): thread 2, count = 143, unlocking mutexinc_count(): thread 3, count = 144, unlocking mutexinc_count(): thread 2, count = 145, unlocking mutexMain(): Waited and joined with 3 threads. Final value of count = 145. Done.