多进程之间的共享资源互斥

 #include    <stdio.h>
 #include    <stdlib.h>
 #include    <unistd.h>
 #include    <fcntl.h>
 #include    <sys/mman.h>
 #include    <pthread.h>
 pthread_mutex_t* g_mutex;
 //创建共享的mutex
 void init_mutex(void)
 {
     int ret;
     //g_mutex一定要是进程间可以共享的，否则无法达到进程间互斥
     g_mutex=(pthread_mutex_t*)mmap(NULL, sizeof(pthread_mutex_t), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
     if( MAP_FAILED==g_mutex )
     {
         perror("mmap");
         exit(1);
     }

     //设置attr的属性
     pthread_mutexattr_t attr;
     pthread_mutexattr_init(&attr);
     //一定要设置为PTHREAD_PROCESS_SHARED
     //具体可以参考http://blog.chinaunix.net/u/22935/showart_340408.html
     ret=pthread_mutexattr_setpshared(&attr,PTHREAD_PROCESS_SHARED);
     if( ret!=0 )
     {
         perror("init_mutex pthread_mutexattr_setpshared");
         exit(1);
     }
     pthread_mutex_init(g_mutex, &attr);
 }
 int main(int argc, char *argv[])
 {
     init_mutex();
     int ret;
     char str1[]="this is child process/r/n";
     char str2[]="this is father process/r/n";
     int fd=open("tmp", O_RDWR|O_CREAT|O_TRUNC, 0666);
     if( -1==fd )
     {
         perror("open");
         exit(1);
     }
     pid_t pid;
     pid=fork();
     if( pid<0 )
     {
         perror("fork");
         exit(1);
     }
     else if( 0==pid )
     {
         ret=pthread_mutex_lock(g_mutex);
         if( ret!=0 )
         {
             perror("child pthread_mutex_lock");
         }
         sleep(10);//测试是否能够阻止父进程的写入
         write(fd, str1, sizeof(str1));
         ret=pthread_mutex_unlock(g_mutex);
         if( ret!=0 )
         {
             perror("child pthread_mutex_unlock");
         }
     }
     else
     {
         sleep(2);//保证子进程先执行
         ret=pthread_mutex_lock(g_mutex);
         if( ret!=0 )
         {
             perror("father pthread_mutex_lock");
         }
         write(fd, str2, sizeof(str2));
         ret=pthread_mutex_unlock(g_mutex);
         if( ret!=0 )
         {
             perror("father pthread_mutex_unlock");
         }
     }
     wait(NULL);
     munmap(g_mutex, sizeof(pthread_mutex_t));