Impossible stack traces

[Markus Gronlund]

Hi,

Thanks for bringing this to attention. I have tried to reproduce this issue today but I am yet unable to do so.

Is it possible for you to provide a reproducer?

Thanks
Markus

-----Original Message-----
From: hysoqvs0sb8 at tutanota.com <hysoqvs0sb8 at tutanota.com> 
Sent: den 23 september 2020 22:07
To: hotspot-jfr-dev at openjdk.java.net
Subject: Impossible stack traces

Hello,

Lately I have noticed that sometimes my method profiling events show stack traces that should not happen under any circumstances.

As an example, there is a class that looks roughly like this:

class SomeClass { 
      private Map<Integer, SomeOtherClass> map = new HashMap<>();
     ...
     map.put(0, new SomeOtherClass());
     map.put(1, new SomeOtherClass());     
     ...
     public SomeOtherClass get(int key) {          return map.get(key);     }}

I have confirmed that the map only ever holds those two keys.
The top of some stack traces captured by method profiling events then look like this:

HashMap$TreeNode java.util.HashMap$TreeNode.getTreeNode(int, Object) 
     HashMap$Node java.util.HashMap.getNode(Object)          Object java.util.HashMap.get(Object)               	SomeOtherClass SomeClass.get(int)

I have ran into this issue with jdk15 and some later ea builds, on windows, and 1ms sampling periods, can any of these be the cause of this issue?

with best regards,
Zsolt N.