[External] : Re: Ephemeral threads

[Alex Otenko]

Because a push iterator isn't the same as a generator.

The code interacting with a generator is like two threads joined with a 0
capacity queue.

On Tue, 13 Jan 2026, 10:17 Remi Forax, <forax at univ-mlv.fr> wrote:

> It starts to be off topic,
> but it's not clear to me that in Java we want to map a generator to an
> iterator and not to stream (a push iterator with a cleanup semantics).
>
> regards,
> Rémi
>
> ------------------------------
>
> *From: *"Alex Otenko" <oleksandr.otenko at gmail.com>
> *To: *"Alan Bateman" <alan.bateman at oracle.com>
> *Cc: *"loom-dev" <loom-dev at openjdk.org>
> *Sent: *Tuesday, January 13, 2026 10:28:13 AM
> *Subject: *Re: [External] : Re: Ephemeral threads
>
> Yes, I understand that now that's not easy to do in Java. I just don't
> think it's all that exotic, and certainly not a bug. After all, we've all
> written at least one iterator when we did a coding interview.
>
> There is 1:1 correspondence between the iterators and the generators. So
> if we can GC the iterators without special dance, we should be able to do
> that for the generators. You could see an iterator as an explicit
> declaration that you are not going to use any features that rely on there
> being a finally - no unlocking, no resource management outside of what a
> finalizer can achieve, no peer to coordinate with, etc. Likewise an
> explicit declaration by an engineer that this here piece of code entering a
> wait is perfectly fine to GC, doesn't seem all that different.
>
> Yes, in general there are thread semantics, try-finally, reference loops
> and other obstacles - but we don't need to solve a general case, just the
> one that is in 1:1 correspondence with the iterators.
>
> I understand that there may be safe ways to implement the same with the
> existing mechanisms - like, the user of the generator might wrap the
> interaction in a try-with-resource, and that way control the lifecycle
> explicitly.
>
> On Tue, 13 Jan 2026, 08:00 Alan Bateman, <alan.bateman at oracle.com> wrote:
>
>>
>>
>> On 13/01/2026 06:42, Alex Otenko wrote:
>> >
>> > I think there are plenty of designs with generators, iterators and
>> > async where non-termination is not a bug.
>>
>> That is true is some other languages/runtimes. If Java were to add
>> generators or some other exotic control flow in the future then there
>> would be more spooky issues to work through, some of which overlap with
>> the spooky issues that have come up in the discussion here.
>>
>> -Alan
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/loom-dev/attachments/20260116/dff4aff5/attachment.htm>