1 #include <pthread.h>
 2 #include <stdio.h>
 3 #include <unistd.h>
 4
 5 #define NUM_THREADS 3
 6 #define TCOUNT      10
 7 #define COUNT_LIMIT 10
 8
 9 int count = 0;
10 int thread_ids[3] = {0,1,2};
11 pthread_mutex_t count_mutex;
12 pthread_cond_t  count_threshold_cv;
13
14 void *inc_count(void *idp)
15 {
16     int i = 0;
17     int taskid = 0;
18     int *my_id = (int*)idp;
19
20     for (i=0; i<TCOUNT; i++) {
21         pthread_mutex_lock(&count_mutex);
22         taskid = count;
23         count++;
24
25         /*
26           唤醒一个阻塞在该条件变量到线程
27           如果没有线程被阻塞在条件变量上，那么调用pthread_cond_signal()将没有作用
28         */
29         pthread_cond_signal(&count_threshold_cv);
30
31         printf("inc_count(): thread %d, count = %d, unlocking mutex\n", *my_id, count);
32         pthread_mutex_unlock(&count_mutex);
33         sleep(1);
34     }
35     printf("inc_count(): thread %d, Threshold reached.\n", *my_id);
36
37     pthread_exit(NULL);
38 }
39
40 void *watch_count(void *idp)
41 {
42     int *my_id = (int*)idp;
43     printf("Starting watch_count(): thread %d\n", *my_id);
44
45     pthread_mutex_lock(&count_mutex);
46     while(count<COUNT_LIMIT) {
47         sleep(3);
48         /*
49           函数将自动/原子到解锁mutex参数指向的互斥锁，并使当前线程阻塞在cv参数指向的条件变量上
50           被阻塞的线程可以被pthread_cond_signal函数，pthread_cond_broadcast函数唤醒，也可能在被信号中断后被唤醒
51           pthread_cond_wait函数的返回并不意味着条件的值一定发生了变化，必须重新检查条件的值.
52           本例子中使用类COUNT_LIMIT最为满足条件的值
53           pthread_cond_wait函数返回时，相应的互斥锁将被当前线程锁定，即使是函数出错返回
54         */
55         pthread_cond_wait(&count_threshold_cv, &count_mutex);
56         printf("watch_count(): thread %d Condition signal received.\n", *my_id);
57     }
58
59     count += 100;
60     pthread_mutex_unlock(&count_mutex);
61     pthread_exit(NULL);
62 }
63
64 int main (int argc, char *argv[])
65 {
66     int i, rc;
67     pthread_t threads[3];
68     pthread_attr_t attr;
69
70     /* Initialize mutex and condition variable objects */
71     pthread_mutex_init(&count_mutex, NULL);
72     pthread_cond_init (&count_threshold_cv, NULL);
73
74     /* For portability, explicitly create threads in a joinable state */
75     pthread_attr_init(&attr);
76     pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
77     pthread_create(&threads[0], &attr, inc_count,   (void *)&thread_ids[0]);
78     pthread_create(&threads[1], &attr, inc_count,   (void *)&thread_ids[1]);
79     pthread_create(&threads[2], &attr, watch_count, (void *)&thread_ids[2]);
80
81     /* Wait for all threads to complete */
82     for (i=0; i<NUM_THREADS; i++) {
83         pthread_join(threads[i], NULL);
84     }
85     printf ("Main(): Waited on %d  threads. Done.\n", NUM_THREADS);
86
87     /* Clean up and exit */
88     pthread_attr_destroy(&attr);
89     pthread_mutex_destroy(&count_mutex);
90     pthread_cond_destroy(&count_threshold_cv);
91     pthread_exit(NULL);
92
93     return 0;
94 }