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

Tue Dec 5 01:44:36 UTC 2023

On Tue, 5 Dec 2023 01:20:28 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> VM_HeapDumper caches stack traces for platform/carrier and mounted virtual threads only.
> For unmounted virtual threads ThreadDumper objects are created on the stack (see `VM_HeapDumper::dump_vthread`), so I don't see problems with memory usage even huge number of unmounted vthreads.
> I think an option to exclude stack traces from heap dump is a separate task.

I was actually referring to the footprint of the hprof file, not the in process memory usage while producing it.

My concern with not doing the option to exclude stack traces now is that it could result in some unusable or unmanageably large heap dumps, or tools simply being overwhelmed by the number of threads. For example, I just looked at the VisualVM threads view, and it just produces a scrollable list of all threads. What happens if there are suddenly 10's of thousands if not millions of threads? If we are lucky is doesn't choke on them and the platform threads are first in the list, but this is the type of thing I'd like to see testing of before pushing this change.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/16665#issuecomment-1839855843