四十一、Linux 线程——线程同步之条件变量

1 #include <pthread.h>
2 int pthread_cond_init(pthread_cond_t *restrict cond, pthread_condattr_t *restrict attr);
3 int pthread_cond_destroy(pthread_cond_t *cond);

1 #include <pthread.h>
2 int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);
3 int pthread_cond_timewait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex, const struct timespec *restrict timeout);
4 
5 struct timespec {
6     time_t tv_sec;  /** seconds */ 
7     ong tv_nsec;    /** nanoseconds */ 
8 };

1 #include <pthread.h>
2 int pthread_cond_signal(pthread_cond_t *cond);
3 int pthread_cond_broadcast(pthread_cond_t *cond);

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <pthread.h>
 4 #include <unistd.h>
 5 
 6 /** 两个线程定义的共享资源 */
 7 typedef struct {
 8     int res;
 9     int is_wait;    ///< 用户给出的用于判断的条件
10     pthread_cond_t cond;    ///< 条件变量
11     pthread_mutex_t mutex;  ///< 互斥锁
12 }Result;
13 
14 
15 /** 计算并将结果放置在 Result 中的线程运行函数 */
16 void *set_fn(void *arg)
17 {
18     Result *r = (Result *)arg;
19     int i = 0;
20     int sum = 0;
21 
22     for(; i <= 100; i++){
23         sum += i;
24     }
25 
26     /** 将结果放置到 Result 中 */
27     r->res = sum;
28 
29     pthread_mutex_lock(&r->mutex);
30     /** 判断获取结果的线程是否准备好 */
31     while(!r->is_wait){
32         pthread_mutex_unlock(&r->mutex);
33         usleep(100);
34         pthread_mutex_lock(&r->mutex);
35     }
36     pthread_mutex_unlock(&r->mutex);
37 
38     /** 通知唤醒等待的那个获取结果的线程 */
39     pthread_cond_broadcast(&r->cond);
40 
41     return (void *)0;
42 }
43 
44 /** 获得结果的线程运行函数 */
45 void *get_fn(void *arg)
46 {
47     Result *r = (Result *)arg;
48 
49     /** 对两个线程共享的判断条件进行保护（加锁） */
50     /** 两个线程对判断条件的操作是互斥的 */
51     pthread_mutex_lock(&r->mutex);
52     /** 当线程启动后，将此变量设置为1，代表此线程已经准备好了 */
53     r->is_wait = 1;
54 
55     /** 获取结果的线程等待 */
56     pthread_cond_wait(&r->cond, &r->mutex);
57 
58     /** 被唤醒后 */
59     pthread_mutex_unlock(&r->mutex);
60 
61     /** 去获取计算结果 */
62     int res = r->res;
63     printf("0x%lx get sum is %d\n", pthread_self(), res);
64 
65     return (void *)0;
66 }
67 
68 int main(void)
69 {
70     int err;
71     pthread_t cal, get;
72 
73     Result r;
74     r.is_wait = 0;
75     pthread_cond_init(&r.cond, NULL);
76     pthread_mutex_init(&r.mutex, NULL);
77 
78     /** 启动获取结果的线程 */
79     if((err = pthread_create(&get, NULL, get_fn, (void *)&r)) != 0){
80         perror("pthread create error");
81     }
82 
83     /** 启动计算结果的线程 */
84     if((err = pthread_create(&cal, NULL, set_fn, (void *)&r)) != 0){
85         perror("pthread create error");
86     }
87 
88     pthread_join(cal, NULL);
89     pthread_join(get, NULL);
90 
91     pthread_cond_destroy(&r.cond);
92     pthread_mutex_destroy(&r.mutex);
93 
94     pthread_cond_destroy(&r.cond);
95     pthread_mutex_destroy(&r.mutex);
96     return 0;
97 }