flock

/*
 *  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__
    rb_io_t *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);
}