About flattening a nullable j.l.Long

[David Alayachew]

💖

David reacted via Gmail
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On Fri, Nov 7, 2025, 10:13 AM Frederic Parain <frederic.parain at oracle.com>
wrote:

> Here's a write-up from John Rose on this subject:
>
>
> https://cr.openjdk.org/~jrose/values/NullabilityRequiresConsistency.java.txt
>
> Fred
>
>
> On 11/7/25 05:39, Tobias Hartmann wrote:
> > Right, the example provided by Rémi shows the issue. The null marker
> > needs to be written atomically with the payload.
> >
> > Best regards,
> > Tobias
> >
> >
> > On 11/6/25 2:02 PM, Remi Forax wrote:
> >> Hello,
> >> as far as i remember, the problem is that you can resurrect a value,
> >> for example with a Long
> >>
> >> Thread1
> >>    a.x = new Long(12);
> >>    a.x = null;
> >>    IO.println(a.x); //12
> >>
> >> Thread2
> >>    IO.println(a.x);  // null
> >>    a.x = new Long(77);   // descheduled in between writing the maker
> >> and writing the long
> >>
> >>
> >> The thread1 can see the Long(12) to be resurrected, something that is
> >> not possible with references.
> >>
> >> regards,
> >> Rémi
> >>
> >>
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> >>
> >>
> >>     *From: *"Quân Anh Mai" <anhmdq at gmail.com>
> >>     *To: *"David Alayachew" <davidalayachew at gmail.com>
> >>     *Cc: *"valhalla-dev" <valhalla-dev at openjdk.org>
> >>     *Sent: *Thursday, November 6, 2025 3:52:41 AM
> >>     *Subject: *Re: About flattening a nullable j.l.Long
> >>
> >>     Ah yes, my bad, it is
> >> https://github.com/openjdk/valhalla/pull/1720
> >> <https://github.com/openjdk/valhalla/pull/1720>
> >>
> >>     On Thu, 6 Nov 2025 at 07:26, David Alayachew
> >> <davidalayachew at gmail.com <mailto:davidalayachew at gmail.com>> wrote:
> >>
> >>         Just a heads up, your [1] is a dead link. Can you try to put
> >> the url in again?
> >>
> >>         On Wed, Nov 5, 2025, 2:06 PM Quân Anh Mai <anhmdq at gmail.com
> >> <mailto:anhmdq at gmail.com>> wrote:
> >>
> >>             Hi,
> >>             Currently, I'm having a PR that allows flattening of a
> >> nullable value class with a 64-bit payload [1]. Dan Smith told me
> >> that some ideas along these lines were discussed a few years ago, and
> >> the consensus was that it was a dead end. May I ask what the concerns
> >> were, and whether they are still relevant now?
> >>
> >>             Thanks a lot,
> >>             Quan Anh
> >>
> >>
> >
>
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