Ephemeral threads

[Andrew Haley]

On 09/01/2026 13:03, Viktor Klang wrote:
>   From my perspective, the big issue with ephemerality of VTs is that it
> easily leads to problems where resources leak with no trace of who
> leaked it—which tends to be rather nightmarish to deal with once they
> pop up in production—"Hey, why is this semaphore unbalanced?!".

I don't understand what scenario you're talking about.

How, exactly, would you make a thread unreachable? It can't be on any 
reachable queue, so it isn't waiting on a timer or I/O. It can't be 
running, because the it's trivially reachable.

Maybe it's waiting on some kind of semaphore that has become 
unreachable. In that case, the thread cannot make any progress. It makes 
no difference whether you GC it or not. The native resources it holds 
will never be released. Semantically, an unreachable thread is not a 
thing: it has no properties.

Therefore, any thread that is unreachable may be GC'd, surely.

I guess I may be missing some way that an unreachable thread is 
observable? If so, what is it?

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
https://keybase.io/andrewhaley
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