pthead_cond_t 的使用
源代码1：
1 #include <stdio.h>
2 #include <pthread.h>
3 #include <stdlib.h>
4 #include <unistd.h>
5
6 pthread_cond_t qready = PTHREAD_COND_INITIALIZER;
7 pthread_mutex_t qlock = PTHREAD_MUTEX_INITIALIZER;
8 int constant = 0;
9
10 void *prints(void *arg)
11 {
12 pthread_mutex_lock(&qlock);
13 pthread_t tid = pthread_self();
14 while (constant <10)
15 {
16 pthread_cond_wait(&qready, &qlock);
17 }
18 printf("After while thread %u, Constant is %d\n",
19 (unsigned int)tid, constant);
20 pthread_mutex_unlock(&qlock);
21 pthread_exit((void *)tid);
22 }
23
24 void *incre(void *arg)
25 {
26 pthread_mutex_lock(&qlock);
27 pthread_t tid = pthread_self();
28 while ( ++constant < 20)
29 {
30 printf("In while thread %u, Constant is %d\n",
31 (unsigned int)tid, constant);
32
33 if (constant == 10) { // 注意这里
34 pthread_mutex_unlock(&qlock);
35 pthread_cond_signal(&qready);
36 pthread_mutex_lock(&qlock);
37 }
38 }
39 printf("Now the constant is %d\n", constant);
40 /*
41 constant += 10;
42 if (constant == 10)
43 pthread_cond_signal(&qready);
44 */
45 pthread_mutex_unlock(&qlock);
46
47 pthread_exit((void *)tid);
48 }
49
50 int main()
51 {
52 int err;
53 pthread_t tid0, tid1;
54
55 err = pthread_create(&tid0, NULL, prints, NULL);
56 if (err != 0)
57 {
58 printf("can't create thread: %d \n", strerror(err));
59 exit(0);
60 }
61
62 sleep(1);
63 err = pthread_create(&tid1, NULL, incre, NULL);
64 if (err != 0)
65 {
66 printf("can't create thread: %d \n", strerror(err));
67 exit(0);
68 }
69 sleep(1);
70
71 exit(0);
72 }
运行结果1：
源代码2：
1 #include <stdio.h>
2 #include <pthread.h>
3 #include <stdlib.h>
4 #include <unistd.h>
5
6 pthread_cond_t qready = PTHREAD_COND_INITIALIZER;
7 pthread_mutex_t qlock = PTHREAD_MUTEX_INITIALIZER;
8 int constant = 0;
9
10 void *prints(void *arg)
11 {
12 pthread_mutex_lock(&qlock);
13 pthread_t tid = pthread_self();
14 while (constant <10)
15 {
16
17 pthread_cond_wait(&qready, &qlock);
18 }
19 printf("After while thread %u, Constant is %d\n",
20 (unsigned int)tid, constant);
21 pthread_mutex_unlock(&qlock);
22 pthread_exit((void *)tid);
23 }
24
25 void *incre(void *arg)
26 {
27 pthread_mutex_lock(&qlock);
28 pthread_t tid = pthread_self();
29 while ( ++constant < 20)
30 {
31 printf("In while thread %u, Constant is %d\n",
32 (unsigned int)tid, constant);
33
34 if (constant == 10) { // 注意这里
35 // pthread_mutex_unlock(&qlock);
36 pthread_cond_signal(&qready);
37 // pthread_mutex_lock(&qlock);
38 }
39 }
40 printf("Now the constant is %d\n", constant);
41 /*
42 constant += 10;
43 if (constant == 10)
44 pthread_cond_signal(&qready);
45 */
46 pthread_mutex_unlock(&qlock);
47
48 pthread_exit((void *)tid);
49 }
50
51 int main()
52 {
53 int err;
54 pthread_t tid0, tid1;
55
56 err = pthread_create(&tid0, NULL, prints, NULL);
57 if (err != 0)
58 {
59 printf("can't create thread: %d \n", strerror(err));
60 exit(0);
61 }
62
63 sleep(1);
64 err = pthread_create(&tid1, NULL, incre, NULL);
65 if (err != 0)
66 {
67 printf("can't create thread: %d \n", strerror(err));
68 exit(0);
69 }
70 sleep(1);
71
72 exit(0);
73 }
运行结果：
其中，虽然函数pthread_wait_cond()之前，该线程已经持有锁。但是在该函数阻塞时，将释放掉锁。因此，只有只有锁的线程释放掉，才能继续从pthread_wait_cond()之后执行，因为该函数将再次获得锁的控制权。
