Ceki,

I've never tried -Djdk.tracePinnedThreads=full as Alan mentioned but here is what worked for me:

• Run the test with "-Djdk.trackAllThreads=true"
• Once it hangs, run "jcmd <pid> Thread.dump_to_file <filename>" from a terminal

This will give you a thread dump containing virtual threads (unlike the old mechanism which only shows carrier threads).