(S) RFR: 8154710: [Solaris] Investigate use of in-memory low-resolution timestamps for Java and internal time API's

[David Holmes]

bug: https://bugs.openjdk.java.net/browse/JDK-8154710
webrev: http://cr.openjdk.java.net/~dholmes/8154710/webrev/

This change is small in nature but somewhat broad in scope. It "affects" 
the implementation of System.currentTimeMillis() in the Java space, and 
os::javaTimeMillis() in the VM. But on Solaris only.

I say "affects" but the change will be unobservable other than in terms 
of performance.

As of Solaris 11.3.6 a new in-memory timestamp has been made available 
(not unlike what has always existed on Windows). There are actually 3 
different timestamps exported but the one we are interested in is 
get_nsecs_fromepoch - which is of course elapsed nanoseconds since the 
epoch - which is exactly what javaTimeMillis() is, but expressed in 
milliseconds. The in-memory timestamps have an update accuracy of 1ms, 
so are not suitable for any other API's that want the time-of-day, but 
at a greater accuracy.

Microbenchmark shows the in-memory access is approx 45% faster (19ns on 
my test system) compared to the gettimeofday call (35ns).

Thanks,
David