Perl 多进程文件锁

fcntl FILEHANDLE,FUNCTION,SCALAR

Implements the fcntl(2) function. You'll probably have to say

  
    

   
      
   
     use
   
      
   
     Fcntl
   
     ;
  
    

first to get the correct constant definitions. Argument processing and value returned work just like ioctlbelow. For example:

  
    

   
     use
   
      
   
     Fcntl
   
     ;

   
     fcntl
   
     (
   
     $filehandle
   
     ,
   
      F_GETFL
   
     ,
   
      
   
     $packed_return_buffer
   
     )
 or 
   
     die
   
      
   
     "
   
     can't fcntl F_GETFL: $!
   
     "
   
     ;  
  
    

You don't have to check for defined on the return from fcntl. Like ioctl, it maps a 0 return from the system call into "0 but true" in Perl. This string is true in boolean context and 0 in numeric context. It is also exempt from the normal -w warnings on improper numeric conversions.

Note that fcntl raises an exception if used on a machine that doesn't implement fcntl(2). See the Fcntl module or your fcntl(2) manpage to learn what functions are available on your system.

Here's an example of setting a filehandle named REMOTE to be non-blocking at the system level. You'll have to negotiate $| on your own, though.

  
    

   
     use
   
      
   
     Fcntl
   
      qw(F_GETFL F_SETFL O_NONBLOCK);

   
     $flags
   
      
   
     =
   
      
   
     fcntl
   
     (REMOTE
   
     ,
   
      F_GETFL
   
     ,
   
      
   
     0
   
     )
 or 
   
     die
   
      
   
     "
   
     Can't get flags for the socket: $!\n
   
     "
   
     ;

   
     $flags
   
      
   
     =
   
      
   
     fcntl
   
     (REMOTE
   
     ,
   
      F_SETFL
   
     ,
   
      
   
     $flags
   
      
   
     |
   
      O_NONBLOCK)
 or 
   
     die
   
      
   
     "
   
     Can't set flags for the socket: $!\n
   
     "
   
     ;