RFR: 7194254 jstack reports wrong thread priorities

[David Holmes]

This is a formal request for review for the patch contributed by Dymtro 
Sheyko as discussed previously here:

http://mail.openjdk.java.net/pipermail/hotspot-dev/2012-August/006376.html

I am one reviewer of course.

The webrev is here:

http://cr.openjdk.java.net/~dholmes/7194254/webrev.v1/

The fix has two components:

1. It fixes a bug in os::get_priority that assumed a more positive 
integer was always higher priority than a less positive one.

2. It addresses the problem that os::get_priority is often inexact when 
desiring the Java thread priority (because the mapping from Java 
priority to OS priority is often M:1) by not using it in 
Threads::print_on. Instead Threads::print_on will always report the 
native OS priority, and JavaThread::print_on() will print the 
java.lang.Thread.getId() value together with the 
java.lang.Thread.getPriority() value.

This change in output affects all stackdumps including crash logs and 
thread dumps (including those shown by jstack).

There is also a test program to check jstack output. I'll be doing some 
additional validation while the RFR is in progress.

Thanks,
David