一个简单的互斥量的例子

柔光的暖阳◎ 2021-10-29 19:30 348阅读 0赞

1。 互斥量

Linux提供了控制线程执行和访问代码临界区域的方法。其中最基本的两种办法是信号量和互斥量。

关于信号量，笔者在 [Linux信号量介绍][Linux]中介绍

本文只介绍semaphore.h 相关的信号量的简单的操作。关于信号量在笔者其他博客里有详细介绍。

Linux还有其他共享内存的方法。

2. 与互斥量相关的函数

\# **include**  <pthread.h >  
  
     **int** pthread\_mutex\_init(pthread\_mutex\_t \*mutex, pthread\_mutexattr\_t \*mutexattr); //创建互斥量  
  
     **int** pthread\_mutex\_lock(pthread\_mutex\_t \*mutex); //加锁  
  
     **int** pthread\_mutex\_unlock(pthread\_mutex\_t \*mutex); //解锁  
  
     **int** pthread\_mutex\_destroy(pthread\_mutex\_t \*mutex); //清理互斥量

3. 一个简单的程序例子

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*  
 \*    @file            mutex.c  
 \*    @brief        互斥锁  
 \*    @author        Windeal  
 \*    @date        2013/08/06  
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/  
   
\# **include**  <stdlib.h >  
\# **include**  <stdio.h >  
\# **include**  <unistd.h >  
\# **include**  <string.h >  
\# **include**  <pthread.h >  
   
\# **define** WORK\_SIZE  1024  
**char** work\_area\[WORK\_SIZE\];  
   
pthread\_mutex\_t work\_mutex;  
   
**int** time\_to\_exit  = 0;  
   
**void**  \*thread\_function( **void**  \*arg);  
   
**int** main( **int** argc, **char** \* argv\[\])  
\{  
     **int** ret;  
    pthread\_t a\_thread;  
     **void**  \*thread\_result;  
   
    ret = pthread\_mutex\_init( &work\_mutex, NULL);  
     **if** (ret  != 0) \{  
        perror( "pthread\_mutex\_init failed\\n");  
        exit(EXIT\_FAILURE);  
    \}  
   
   
   
    printf( "It time to create a thread!\\n");    /  
    ret = pthread\_create( &a\_thread, NULL, thread\_function, NULL);  
     **if** (ret  != 0) \{  
        perror( "Thread creation failed!\\n");  
        exit(EXIT\_FAILURE);  
    \}  
   
    pthread\_mutex\_lock( &work\_mutex);     //加锁  
    printf( "Input some text. Enter \\"end\\" to finished\\n");  
     **while** ( !time\_to\_exit) \{         //  
        fgets(work\_area, WORK\_SIZE, stdin);  
        pthread\_mutex\_unlock( &work\_mutex);  // 解锁  
         **while** ( 1) \{  
            pthread\_mutex\_lock( &work\_mutex);     //加锁  
             **if** (work\_area\[ 0\] != '\\0')\{         //如果有数据则到解锁，没有数据则继续输入  
                pthread\_mutex\_unlock( &work\_mutex); // 解锁 因为workarea里有数据  
                                     //因此到另一个线程里比对  
                sleep( 1);  
            \}  
             **else** \{  
                 **break**;  
            \}  
        \}  
    \}  
   
    pthread\_mutex\_unlock( &work\_mutex);  // 解锁  
    printf( "Waiting for thread finish!\\n");  /  
    ret = pthread\_join(a\_thread,  &thread\_result);  
     **if** (ret  != 0) \{  
        perror( "Thread finished failed\\n");  
        exit(EXIT\_FAILURE);  
    \}  
   
    printf( "Thread joined\\n");  
    pthread\_mutex\_destroy( &work\_mutex);  
    exit(EXIT\_SUCCESS);  
   
\}  
   
**void**  \*thread\_function( **void**  \* arg) \{  
    sleep( 1);  
    pthread\_mutex\_lock( &work\_mutex);  
     **while** (strncmp( "end", work\_area, 3) != 0) \{  
        printf( "You have enter %d charactor\\n", strlen(work\_area) \- 1);  
        work\_area\[ 0\]  = '\\0';     //清零数据区  
        pthread\_mutex\_unlock( &work\_mutex);      //让主线程继续输入数据  
        sleep( 1);  
        pthread\_mutex\_lock( &work\_mutex);   //尝试加锁，如果主线程已输入数据，则加锁成功  
         **while** (work\_area\[ 0\] == '\\0') \{     //如果输入为空，则继续等待输入.输入不为空时，跳出循环  
            pthread\_mutex\_unlock( &work\_mutex);  
            sleep( 1);  
            pthread\_mutex\_lock( &work\_mutex);  
        \}  
    \}  
   
    time\_to\_exit =  1;  
    work\_area\[ 0\] = '\\0';  
    pthread\_mutex\_unlock( &work\_mutex);  
    pthread\_exit( 0);  
   
\}

结果如下所示：

![SouthEast][]

![Image 1][]

[Linux]: http://blog.csdn.net/windeal/article/details/9962349
[SouthEast]: /images/20211029/0de319e4ccc842b486a49396717432ac.png
[Image 1]: