The native thread priority code on Solaris is disabled by default (UseThreadPriorities==false). The code seems to have bit-rotted as enabling it triggers an assertion failure:

 > ./build/solaris-x64-debug/images/jdk/bin/java -XX:+UseThreadPriorities -version
# To suppress the following error report, specify this argument# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=
/os_solaris.cpp# after -XX: or in .hotspotrc: SuppressErrorAt=/os_solaris.cpp:3486
:3486# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=
/os_solaris.cpp[thread 4 also had an error]
:3486
[thread 6 also had an error]
[thread 5 also had an error]
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/scratch/dh198349/jdk9-hs-rt/hotspot/src/os/solaris/vm/os_solaris.cpp:3486), pid=25072, tid=3
# assert(newpri >= 0 && newpri <= 127) failed: bad priority mapping
#
# JRE version: (9.0) (fastdebug build )
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 9-internal+0-2016-02-03-193213.daholme.jdk9-hs-rt, mixed mode, tiered, compressed oops, g1 gc, solaris-amd64)
# Core dump will be written. Default location: /scratch/dh198349/jdk9-hs-rt/core or core.25072
#
[thread 13 also had an error]
# An error report file with more information is saved as:
# /scratch/dh198349/jdk9-hs-rt/hs_err_pid25072.log
[thread 14 also had an error]
#
# If you would like to submit a bug report, please visit:
# http://bugreport.java.com/bugreport/crash.jsp
#
Current thread is 3
Dumping core ...


Fail with ThreadPriorityPolicy 0 and 1.