file.flock (locking_constant ) →  0 or false

Locks or unlocks a file according to locking_constant (a logical or of the values in the table below). Returns false if File::LOCK_NB is specified and the operation would otherwise have blocked. Not available on all platforms.

Locking constants (in class File):

LOCK_EX   | Exclusive lock. Only one process may hold an
          | exclusive lock for a given file at a time.
----------+------------------------------------------------
LOCK_NB   | Don't block when locking. May be combined
          | with other lock options using logical or.
----------+------------------------------------------------
LOCK_SH   | Shared lock. Multiple processes may each hold a
          | shared lock for a given file at the same time.
----------+------------------------------------------------
LOCK_UN   | Unlock.

Example:

File.new("testfile").flock(File::LOCK_UN)   #=> 0

Source Code

/*
*  call-seq:
*     file.flock (locking_constant ) =>  0 or false
*  
*  Locks or unlocks a file according to <i>locking_constant</i> (a
*  logical <em>or</em> of the values in the table below).
*  Returns <code>false</code> if <code>File::LOCK_NB</code> is
*  specified and the operation would otherwise have blocked. Not
*  available on all platforms.
*     
*  Locking constants (in class File):
*
*     LOCK_EX   | Exclusive lock. Only one process may hold an
*               | exclusive lock for a given file at a time.
*     ----------+------------------------------------------------
*     LOCK_NB   | Don't block when locking. May be combined
*               | with other lock options using logical or.
*     ----------+------------------------------------------------
*     LOCK_SH   | Shared lock. Multiple processes may each hold a
*               | shared lock for a given file at the same time.
*     ----------+------------------------------------------------
*     LOCK_UN   | Unlock.
*
*  Example:
*
*     File.new("testfile").flock(File::LOCK_UN)   #=> 0
*     
*/

static VALUE
rb_file_flock(obj, operation)
   VALUE obj;
   VALUE operation;
{
#ifndef __CHECKER__
   OpenFile *fptr;
   int op;

   rb_secure(2);
   op = NUM2INT(operation);
   GetOpenFile(obj, fptr);

   if (fptr->mode & FMODE_WRITABLE) {
       fflush(GetWriteFile(fptr));
   }
 retry:
   if (flock(fileno(fptr->f), op) < 0) {
       switch (errno) {
         case EAGAIN:
         case EACCES:
#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
         case EWOULDBLOCK:
#endif
             return Qfalse;
         case EINTR:
#if defined(ERESTART)
         case ERESTART:
#endif
           goto retry;
       }
       rb_sys_fail(fptr->path);
   }
#endif
   return INT2FIX(0);
}