[8u] RFA (S) 8059677: Thread.getName() instantiates Strings

[Aleksey Shipilev]

Hi,

I would like to backport a simple performance optimization to 8u:
  https://bugs.openjdk.java.net/browse/JDK-8059677

This change was in JDK 9 for at least a year now, and no problems were
apparently discovered. The change comes in two parts:
  http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/9dc4d4fc73ca
  http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/0bddfc90d139

Review thread:

http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-November/029569.html

Note that Roger had specific concerns about backporting, which seem
unproblematic:

http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-November/029589.html

JDK part applies without problems, and HS part needs some fuzz in
vm/runtime/thread.cpp. These are the proposed webrevs against 8u, for
convenience:
  http://cr.openjdk.java.net/~shade/8059677/8u/webrev.01.hs/
  http://cr.openjdk.java.net/~shade/8059677/8u/webrev.01.jdk/

I re-ran full JPRT against 8u with this change, and it was clean.

Cheers,
-Aleksey