linux 下多进程写文件

linux 下多线程给文件加排他锁

   利用flock 函数，具体用户请自己查。

  执行流程

1，创建 /dev/shm/test文件，并打开文件。

2，fork 一个子进程

     在子进程中再次打开文件，目的是不和父进程使用不一样的文件描述符。

3，父子进程各自给文件加排他锁并sleep10秒， 

   然后向文件中写入数据。

 代码如下

 

/* slock.c */
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <stdio.h> 
int main()
{
 
    int fd = open( "/dev/shm/test",O_CREAT|O_RDWR,S_IRWXU|S_IRGRP|S_IWGRP|S_IRWXO );
    if ( fd < 0 )
    {
        puts( "open error" );
        return -1;
    }  
   if (fork () == 0) {      
       int fd1 = open( "/dev/shm/test",O_RDWR);     
       if(flock(fd1,LOCK_EX)==0){
           printf("pid(%d) %s",getpid(), "the file was locked  by child .\n");
           puts( "child sleep now ..." );
           sleep( 10 );
           write(fd, "child\n",strlen("child\n"));
           if(flock(fd1,LOCK_UN)==0){
                puts("child the file was unlocked .\n");
            }     
        }
        close( fd1);
        puts( "child exit..." );
       
    } else { 
        if(flock(fd,LOCK_EX)==0){
            printf("pid(%d) %s",getpid(), "the file was locked by parent .\n");  
            puts( "parent sleep now ..." );
            sleep( 10 );
            write(fd, "parent\n",strlen("parent\n"));
            if(flock(fd,LOCK_UN)==0){
                puts("parent the file was unlocked .\n");
            }       
        }    
       
        puts( "parent exit..." );
        close( fd );
    }
    return 0;
}

执行结果

[root@centos]# ./slockc
pid(1516) the file was locked by parent .
parent sleep now ...
parent the file was unlocked .

parent exit...
[root@centos]# pid(1517) the file was locked  by child .
child sleep now ...
child the file was unlocked .

child exit...

 

最后查看   /dev/shm/test内容

parent
child