[9] RFR (S): 8177963: Parallel GC fails fast when per-thread task log overflows

[Thomas Schatzl]

Hi all,

  can I have reviews for this small fix that changes a guarantee() in
parallel gc when some logging buffer overflows into a warning message
about the overflow and (continued) reuse of the last entry of that
buffer so that the user then can then rerun with a larger buffer.

Since it is so late in the release cycle I would like to keep the fix
simple instead of rewriting the buffer logic, i.e. make it expandable
etc. 

This change has been mostly contributed by Ramki from Twitter, as part
of JDK-7180571; however we just got this bug from release testing that
is a duplicate, and he's unavailable to do an RFR right now, and I want
this fixed asap. I intend to put him as author for this change.

CR:
https://bugs.openjdk.java.net/browse/JDK-8177963
Webrev:
http://cr.openjdk.java.net/~tschatzl/8177963/webrev/
Testing:
local testing, new test, jprt

Thanks,
  Thomas