RFR (S): 8230794: Improve assert to get more information about the JDK-8227695 failure

[Kim Barrett]

> On Sep 10, 2019, at 6:20 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi all,
> 
>  can I have reviews for this change that improves the assert that is
> failing in JDK-8227695?
> 
> We have been unsuccessfully trying to reproduce the problem locally and
> doing tens of thousands runs with the original code to get a better
> idea of the cause. (Or finding the issue with code inspection or by
> tweaking the code)
> 
> This change augments the assert to show more information, and adds it
> in several places to get a better idea of the cause.
> 
> It looks like this issue is caused by extremely specific environmental
> conditions we were unable to reproduce.
> 
> We will remove this debug code later.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8230794
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8230794/webrev/
> Testing:
> hs-tier1-5 without failures :(
> 
> Thanks,
>  Thomas

Looks good.