On 24/08/2025 16:06, David Alayachew wrote:
Thanks for the context Alan and Viktor. I guess since Virtual Threads
kick off tasks so fast (due to their throughput), I never had a chance
to observe this behaviour.
But I think I get it -- once the scope closes, all future calls to
fork() fail, so onFork() simply doesn't get called.
If you stick to try-with-resources and open the STS in the
resource-specification, e.g. try (var scope =
StrcuturedTaskScope.open(..)) { }, then the local variable will not be
in scope in code that follows the try-with-resources statement. This
makes it hard to even attempt to fork after the STS has been closed. If
a reference does escape then it just means that calling fork after the
close will throw IllegalStateException.
That is a very important detail though. Hope you don't mind, but let
me change subject to make sure I understand this behaviour.
For example, let's say I use the anySuccessfulOrThrow Joiner. Then,
theoretically speaking, if I have enough tasks such that by the time
the scope closes, I am still feeding tasks into fork(), then my scope
will fail? Am I understanding that correctly?
This is cancellation rather than closing. It's okay for the scope to be
cancelled during the "forking phase". Once cancelled, it just means that
fork returns a subtask (UNAVAILABLE state) without starting a thread to
execute it. The StrcuturedTaskScope::isCancelled method can be used to
avoid doing unnecessary work in a lengthy forking phase (there's an API
note in the isCancelled method on this).
-Alan.
