多线程同步

Posted 2020-06-17

多线程同步

线程同步

使用条件变量同步线程

初始化

pthread_cond_t cond_ready = PTHREAD_COND_INITIALIZER;

等待条件成熟

Pthread_cond_wait(&cond_ready,&mut);

设置条件成熟

Pthread_cond_signal(&cond_ready);

 

没有使用条件变量同步线程例程：缺点：cpu使用效率低

pthread_sync.c

 

 1 #include <stdio.h>
 2 #include <pthread.h>
 3 
 4 pthread_t thread[2];
 5 int number = 0;
 6 pthread_mutex_t mut;
 7 
 8 void studentA()
 9 {
10     int i;
11     for(i = 0;i < 5;i++)
12     {
13         pthread_mutex_lock(&mut);
14         //扫一次地
15         number++;
16         if(number >=5)
17         {
18             printf("student A has finish his work!\n");
19         }
20         pthread_mutex_unlock(&mut);
21         //休息一秒钟
22         sleep(1);
23     }
24     pthread_exit(NULL);
25 }
26 
27 void studentB()
28 {
29     while(1)
30     {
31         pthread_mutex_lock(&mut);
32         if(number >= 5)//判断A同学是否已经扫完5次地
33         {
34             //拖地
35             number = 0;
36             pthread_mutex_unlock(&mut);
37             printf("student B has finish his work!\n");
38             break;
39         }
40         else
41         {
42             pthread_mutex_unlock(&mut);
43             //睡眠2秒钟
44             sleep(2);
45         }
46     }
47     //退出
48     pthread_exit(NULL);
49 }
50 
51 int main()
52 {
53     //初始化互斥锁
54     pthread_mutex_init(&mut,NULL);
55     //创建A同学线程
56     pthread_create(&thread[0],NULL,studentA,NULL);
57     //创建B同学线程
58     pthread_create(&thread[1],NULL,studentB,NULL);
59     //等待A同学线程结束
60     pthread_join(pthread[0],NULL);
61     //等待B同学线程结束
62     pthread_jion(pthread[1],NULL);
63     
64     return 0;
65 }

pthread_sync.c

 

使用条件变量来线程同步：

pthread_sync.c

 1 #include <stdio.h>
 2 #include <pthread.h>
 3 
 4 pthread_t thread[2];
 5 int number = 0;
 6 pthread_mutex_t mut;
 7 pthread_cond_t cond_read = PTHREAD_COND_INITIALIZER;
 8 
 9 void studentA()
10 {
11     int i;
12     for(i = 0;i < 5;i++)
13     {
14         pthread_mutex_lock(&mut);
15         //扫一次地
16         number++;
17         if(number >=5)
18         {
19             printf("student A has finish his work!\n");
20             pthread_cond_signal(&cond_ready);
21         }
22         pthread_mutex_unlock(&mut);
23         //休息一秒钟
24         sleep(1);
25     }
26     pthread_exit(NULL);
27 }
28 
29 void studentB()
30 {
31     pthread_mutex_lock(&mut);//先上锁
32     if(number < 5)
33     {
34         pthread_cond_wait(&cond_ready,&mut);//如果没有到5次的话先解锁互斥量,再上锁
35     }
36     number = 0;
37     pthread_mutex_unlock(&mut);
38     printf("student B has finish his work!\n");
39     //退出
40     pthread_exit(NULL);
41 }
42 
43 int main()
44 {
45     //初始化互斥锁
46     pthread_mutex_init(&mut,NULL);
47     //创建A同学线程
48     pthread_create(&thread[0],NULL,studentA,NULL);
49     //创建B同学线程
50     pthread_create(&thread[1],NULL,studentB,NULL);
51     //等待A同学线程结束
52     pthread_join(pthread[0],NULL);
53     //等待B同学线程结束
54     pthread_jion(pthread[1],NULL);
55     
56     return 0;
57 }

pthread_sync.c