>Meaning park() doesn’t have to return…. Exception could be thrown and
release never called….
park()
<https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/concurrent/locks/LockSupport.html#park()>
isn't documented to throw any exception, and even if it were to throw an
exception, it would unwind the stack and end up in some
UncaughtExceptionHandler.
>Resources must be used with try blocks (or some logically similar
construct)
I deliberately omitted the try-finally to be able to say this:
try-finally wouldn't help here if the VT is GCed when parked.
On 2026-01-11 05:17, Dmitry Zaslavsky wrote:
Your code would be broken in our case, but it’s broken in “plain” java
case as well.
Meaning park() doesn’t have to return…. Exception could be thrown and
release never called….
Resources must be used with try blocks (or some logically similar
construct)
That’s what we are trying to “manage” by having a library construct.
That library construct ensures (optionally) that finally (clean up)
called up in any case.
The other option I would want to consider is allowing try/finally and
throwing an interrupt exception.
I haven’t played with this. Ideally JVM support that lets me know if
there is a finally block on stack would be nice.
But I know it’s too much to ask.
On Jan 10, 2026, at 7:02 PM, Viktor Klang <[email protected]>
wrote:
Hi Dmitry,
An example can look like:
void method() {
long fileDescriptor = acquireFileDescriptor();
LockSupport.park();
releaseFileDescriptor(fileDescriptor);
}
If an ephemeral VT executes that method, and there are no other
references to that ephemeral VT, then at the point of park(), nothing
can unpark it anymore, and it will then never release the file
descriptor.
>We generally don’t allow try blocks (providing other constructs), we
also very strongly discourage (just a drop short of disallowing) ANY
threading primitives.
I don't see how that can work in practice, because it requires all
users of your constructs to be familiar about exactly how all
third-party logic (including JDK classes) are implemented under the
hood. Perhaps I'm misunderstanding?
On 2026-01-09 17:27, Dmitry Zaslavsky wrote:
Not sure what you mean by native resources?
Do you mean what people would use like try resources?
We generally don’t allow try blocks (providing other constructs), we also very
strongly discourage (just a drop short of disallowing) ANY threading primitives.
Which makes me think that there is a better way to express my point from before.
I think there is actually a common pattern here.
We use VT inside of the lib. We don’t want users to actually use any threads
all.
I think it’s a goal of Alex as well.
We use VT as a way to avoid using threads (if that makes sense).
I think ScopedTasks is going in the same direction. Ideally user just doesn’t
know there are threads.
We use Scala (appealing to Victor ;)) vals and immutable collections is the
norm.
We don’t want users to think about Threads period.
So the thought of "GC roots on a VT … we don’t want that though to ever occur
or we failed ;)
On Jan 9, 2026, at 10:26 AM, Viktor Klang<[email protected]> wrote:
On 2026-01-09 15:39, Dmitry Zaslavsky wrote:
someCollection.apar.map { …. }
Can spin N tasks (Each can get it's VT) If some iteration of the loop throws,
we don’t need to rest of the code to run, it’s costly.
If the task are not actively mounted but previously started and are waiting…
(in our case it’s LockSupport.park) we just want to drop that entire queue and
everything around it….
How do you handle acquired native resources that are yet to be released?
--
Cheers,
√
Viktor Klang
Software Architect, Java Platform Group
Oracle
--
Cheers,
√
Viktor Klang
Software Architect, Java Platform Group
Oracle
--
Cheers,
√
Viktor Klang
Software Architect, Java Platform Group
Oracle
