From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <normalperson@yhbt.net>
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net
X-Spam-Level: 
X-Spam-Status: No, score=-4.0 required=3.0 tests=ALL_TRUSTED,BAYES_00
	shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2
Received: from localhost (dcvr.yhbt.net [127.0.0.1])
	by dcvr.yhbt.net (Postfix) with ESMTP id 8FA0D1F5AE;
	Thu, 16 Jul 2020 00:04:01 +0000 (UTC)
Date: Thu, 16 Jul 2020 00:04:01 +0000
From: Eric Wong <normalperson@yhbt.net>
To: Aaron Patterson <aaron.patterson@gmail.com>
Cc: ruby-core@ruby-lang.org, unicorn-public@yhbt.net
Subject: Re: [ruby-core:99185] [Ruby master Bug#17023] How to prevent String
 memory to be relocated in ruby-ffi
Message-ID: <20200716000401.GA15291@dcvr>
References: <redmine.issue-17023.20200710175402.5550@ruby-lang.org>
 <redmine.journal-86563.20200715200039.5550@ruby-lang.org>
 <20200715233540.GA14457@dcvr>
 <647A6735-04C8-4410-A71A-307A2390CFBD@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <647A6735-04C8-4410-A71A-307A2390CFBD@gmail.com>
List-Id: <unicorn-public.yhbt.net>

Aaron Patterson <aaron.patterson@gmail.com> wrote:
> > On Jul 15, 2020, at 4:35 PM, Eric Wong <normalperson@yhbt.net> wrote:
> > Btw, does rb_gc_register_mark_object pin?  A quick glance at
> > gc.c tells me it doesn't, and I'll need to revert commit
> > 2a6cb76d5010cb763ef5a2c305728465d15eb7c9 in unicorn:
> > https://yhbt.net/unicorn-public/20181226050857.6413-1-e@80x24.org/
> 
> Yes, it does pin.  I’m not super proud of this code, but here
> is where objects passed to rb_gc_register_mark_object get
> pinned:
> 
>   https://github.com/ruby/ruby/blob/c2a6295ec04a191c689d22254ac1ad5d665e27ad/vm.c#L2307-L2320

Ah, missed that, thanks.  So all is well in unicorn (for now).

> I don’t know why the mark object array is an array of arrays
> (I assume so as not to waste space in the array buffer?).
> Maybe this could be a more friendly data structure.

It seems so, since rb_ary_push can double the internal buffer.
Anyways, ko1 made commit
a617afc643e17cea5c1960a60adcd5ffb25fdfe2 r46714
Maybe it can be flattened nowadays and rely on GC.compact
to reclaim unused space.

/me goes back to hacking in Perl 5...