One solution is to implement your own flock in terms of fcntl, and keep track of the lock's state. For example, something like: 
our @lockstat;
sub readlock
{
  my($fh)=@_;
  my $fileno = fileno($fh);
  defined($fileno) or die "Bad filehandle";
  if ($lockstat[$fileno] && $lockstat[$fileno]{count})
  {
    $lockstat[$fileno]{count}++;
  }
  else
  {
    fcntl_lock($fh,F_RDLCK);
    $lockstat[$fileno]{count}=1;
  }
}

sub readunlock
{
  my($fh)=@_;
  my $fileno = fileno($fh);
  defined($fileno) or die "Bad filehandle";

  return unless
    $lockstat[$fileno] and $lockstat[$fileno]{count};

  if (--$lockstat[$fileno]{count} == 0)
  {
    fcntl_lock($fh,F_UNLCK);
  }
}

[download]

You can expand this to cover write locks in a similar way (or write a general myflock that does both read, write, and unlocks). If you're using multiple threads, you'll need to use mutexes to protect the data structures from the different threads. You'll also have to think about how to deal with close.

I seem to recall that Perl has a compile-time option to use its own flock implementation based on fcntl; you may want to look into that as well.

In reply to Re: Fcntl() and multiple filehandles by sgifford
in thread Fcntl() and multiple filehandles by Anonymous Monk

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