Linux中线程的互斥锁

╰+攻爆jí腚メ 2022-11-27 03:09 177阅读 0赞

### Linux中线程的互斥锁 ###

*  线程的互斥
 *   *  互斥锁通信机制
     *   *  ①、锁的创建
         *  ②、互斥锁的相关函数
         *  ③、demo
         *  ④、运行效果及分析

# 线程的互斥 #

## 互斥锁通信机制 ##

### ①、锁的创建 ###

pthread_mutex_t    mutex; // 变量名可以自取

### ②、互斥锁的相关函数 ###

<table> 
 <thead> 
  <tr> 
   <th>函数</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>int pthread_mutex_destroy(pthread_mutex_t *mutex)</td> 
   <td>销毁锁</td> 
  </tr> 
  <tr> 
   <td>int pthread_mutex_init(pthread_mutex_t *restrict _mutex,const pthread_mutexattr_t *attr)</td> 
   <td>初始化锁</td> 
  </tr> 
  <tr> 
   <td>int pthread_mutex_lock(pthread_mutex_t *mutex)</td> 
   <td>上锁</td> 
  </tr> 
  <tr> 
   <td>int pthread_mutex_trylock(pthread_mutex_t *mutex)</td> 
   <td>尝试锁（不管锁没锁住都会立即返回）</td> 
  </tr> 
  <tr> 
   <td>int pthread_mutex_unlock(pthread_mutex_t *mutex)</td> 
   <td>解锁</td> 
  </tr> 
 </tbody> 
</table>

同一时间只能有一个线程获取锁

### ③、demo ###

#include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <pthread.h>
    #include <semaphore.h>
    #include <string.h>
    
    void *thread_function(void *arg);
    
    pthread_mutex_t work_mutex;  //创建锁
    
    #define WORK_SIZE 1024
    char work_area[WORK_SIZE];  //创建全局变量数组
    int time_to_exit = 0;        
    
    int main(int argc,char *argv[]) //主函数
    { 
        int res;
        pthread_t a_thread;  //创建线程ID
        void *thread_result;  
        res = pthread_mutex_init(&work_mutex, NULL); //初始化锁
        if (res != 0) 
    	{ 
            perror("Mutex initialization failed");
            exit(EXIT_FAILURE);
        }
        res = pthread_create(&a_thread, NULL, thread_function, NULL);//创建线程a
        if (res != 0) 
    	{ 
            perror("Thread creation failed");
            exit(EXIT_FAILURE);
        }
        pthread_mutex_lock(&work_mutex);			//上锁
        printf("Input some text. Enter 'end' to finish\n");  
        while(!time_to_exit) 
    	{ 
            fgets(work_area, WORK_SIZE, stdin);		//从标准输入获取数据写入全局变量work_erea
            pthread_mutex_unlock(&work_mutex);		//解锁
            while(1) 
    		{ 
                pthread_mutex_lock(&work_mutex);	//上锁
                if (work_area[0] != '\0')     //等待work_erea中的数据被读完
    			{ 
                    pthread_mutex_unlock(&work_mutex);	//解锁
                    sleep(1);
                }
                else 
    			{ 
                    break;
                }
            }
        }
        pthread_mutex_unlock(&work_mutex);  //解锁
        printf("\nWaiting for thread to finish...\n");
        res = pthread_join(a_thread, &thread_result);   //等待线程A结束 并获取线程的退出码
         if (res != 0) 
    	{ 
            perror("Thread join failed");
            exit(EXIT_FAILURE);
        }
        printf("Thread joined\n");
        pthread_mutex_destroy(&work_mutex);  //销毁锁
        exit(EXIT_SUCCESS);  //退出
    }
    
    void *thread_function(void *arg) //线程的执行函数
    { 
        sleep(1);
        pthread_mutex_lock(&work_mutex);  //上锁
        while(strncmp("end", work_area, 3) != 0) 
    	{ 
            printf("You input %d characters\n", strlen(work_area) -1);  
    		printf("the characters is %s",work_area);  //打印work_erea的数据
    		work_area[0] = '\0';         //把work_erea 置空
            pthread_mutex_unlock(&work_mutex); //解锁
            sleep(1);
            pthread_mutex_lock(&work_mutex);  //上锁
            while (work_area[0] == '\0' ) 
    		{ 
                pthread_mutex_unlock(&work_mutex);  //解锁
                sleep(1);				//睡眠一秒等待主线程写入数据
                pthread_mutex_lock(&work_mutex);  //上锁
            }
        }
        time_to_exit = 1;
        work_area[0] = '\0';  //把work_erea 置空
        pthread_mutex_unlock(&work_mutex);  //解锁
        pthread_exit(0);  //线程退出
    }

### ④、运行效果及分析 ###

**主线程等待输入：**

![在这里插入图片描述][20200813111530303.png_pic_center]

**子线程接收数据：**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTMwOTkxNg_size_16_color_FFFFFF_t_70_pic_center]

**如此循环下去，就做好了线程的同步与互斥**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTMwOTkxNg_size_16_color_FFFFFF_t_70_pic_center 1]

[20200813111530303.png_pic_center]: /images/20221124/c741035f789847ee99210c2338acd014.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTMwOTkxNg_size_16_color_FFFFFF_t_70_pic_center]: /images/20221124/ee98c80dda294770a80e79d67937988e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTMwOTkxNg_size_16_color_FFFFFF_t_70_pic_center 1]: /images/20221124/a19a68407c6445538d0a69767dd4d46c.png