一个简单的互斥量的例子

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：