RFR: 8299426: Heap dump does not contain virtual Thread stack references [v2]

[Chris Plummer]

On 12/4/23 5:20 AM, Alan Bateman wrote:
>
>
> On 04/12/2023 12:41, David Holmes wrote:
>> On 1/12/2023 2:08 pm, Alex Menkov wrote:
>>> On Thu, 30 Nov 2023 21:11:08 GMT, Chris Plummer 
>>> <cjplummer at openjdk.org> wrote:
>>>
>>>> I wasn't thinking in terms of the scheduler somehow no longer 
>>>> references the virtual thread, but instead the program no longer 
>>>> referencing the scheduler (and also not referencing the virtual 
>>>> thread).
>>>
>>> AFAIU unfinished unmounted virtual threads are referenced from other 
>>> objects (they are parked on), so they can't be unreachable even is 
>>> the application is not referencing them and the scheduler.
>>
>> There is (or was - there may be a property that affects this: 
>> trackAllThreads?) a scenario where a VT might park on a 
>> synchronization object which is not referenced from any other thread. 
>> The VT can never be unparked, and the sync object and the VT are 
>> reachable only from either other and so both can be GC'd.
>
> That's right, the door is not closed to introducing ephemeral threads 
> in the future. Right now, virtual threads created directly with the 
> Thread API remaining strongly reachable once started until they 
> terminate. Virtual threads created in other containers (e.g. a 
> thread-per-task ExecutorService) are kept reachable by the container.
>
> -Alan

So does this mean if the application is no longer referencing the 
ExecutorService, then we can have unreachable virtual threads that have 
not completed? This is really the point I've been getting at.

Chris
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