【Linux 编程】pthead_cond_t 的使用

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  }

View Code

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  }

View Code

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。

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原文地址：https://www.cnblogs.com/life91/p/3101009.html