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From: Aaron Patterson <aaron.patterson@gmail.com>
To: Ruby developers <ruby-core@ruby-lang.org>
Cc: unicorn-public@yhbt.net
Subject: Re: [ruby-core:99185] [Ruby master Bug#17023] How to prevent String memory to be relocated in ruby-ffi
Date: Wed, 15 Jul 2020 16:49:38 -0700	[thread overview]
Message-ID: <647A6735-04C8-4410-A71A-307A2390CFBD@gmail.com> (raw)
In-Reply-To: <20200715233540.GA14457@dcvr>



> On Jul 15, 2020, at 4:35 PM, Eric Wong <normalperson@yhbt.net> wrote:
> 
> tenderlove@ruby-lang.org wrote:
>> Right, that makes sense.  I really need to document this (and
>> I apologize for not doing so already), but
>> `rb_gc_register_address` will pin your objects.  When you know
>> you're done with the reference, you can release it with
>> `rb_gc_unregister_address`.  Of course if you don't call the
>> unregister function, the reference will stay alive forever.
> 
> 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

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.

I created a pinned list in compile.c so that objects allocated and used at compile time don’t move (they become free to move once iseq assembly is finished). It seems that might be a more generally useful thing, but so far I’ve only seen two places that need this feature.



  reply	other threads:[~2020-07-15 23:49 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <redmine.issue-17023.20200710175402.5550@ruby-lang.org>
     [not found] ` <redmine.journal-86563.20200715200039.5550@ruby-lang.org>
2020-07-15 23:35   ` [ruby-core:99184] " Eric Wong
2020-07-15 23:49     ` Aaron Patterson [this message]
2020-07-16  0:04       ` [ruby-core:99185] " Eric Wong

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