linux 下多线程写文件

Posted 2020-10-11 蜗牛码

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

 

 1 /* slock.c */
 2 #include <unistd.h>
 3 #include <fcntl.h>
 4 #include <sys/types.h>
 5 #include <sys/stat.h>
 6 #include <string.h>
 7 #include <stdio.h> 
 8 int main()
 9 {
10  
11     int fd = open( "/dev/shm/test",O_CREAT|O_RDWR,S_IRWXU|S_IRGRP|S_IWGRP|S_IRWXO );
12     if ( fd < 0 )
13     {
14         puts( "open error" );
15         return -1;
16     }  
17    if (fork () == 0) {      
18        int fd1 = open( "/dev/shm/test",O_RDWR);     
19        if(flock(fd1,LOCK_EX)==0){
20            printf("pid(%d) %s",getpid(), "the file was locked  by child .\n");
21            puts( "child sleep now ..." );
22            sleep( 10 );
23            write(fd, "child\n",strlen("child\n"));
24            if(flock(fd1,LOCK_UN)==0){
25                 puts("child the file was unlocked .\n");
26             }     
27         }
28         close( fd1);
29         puts( "child exit..." );
30        
31     } else { 
32         if(flock(fd,LOCK_EX)==0){
33             printf("pid(%d) %s",getpid(), "the file was locked by parent .\n");  
34             puts( "parent sleep now ..." );
35             sleep( 10 );
36             write(fd, "parent\n",strlen("parent\n"));
37             if(flock(fd,LOCK_UN)==0){
38                 puts("parent the file was unlocked .\n");
39             }       
40         }    
41        
42         puts( "parent exit..." );
43         close( fd );
44     }
45     return 0;
46 }

执行结果

[[email protected]]# ./slockc
pid(1516) the file was locked by parent .
parent sleep now ...
parent the file was unlocked .

parent exit...
[[email protected]]# 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