RFR(S): 8231457 Asserts on AIX because os::elapsed_counter() is not monotonic

[Zeller, Arno]

Hi,

we have seen assertions on AIX 7.2 on Power9 that complain about negative durations. The issue seems to be caused by the implementation of o::elapsed_counter() on AIX that uses gettimeofday which is not monotonic. To solve the issue I prepared a small patch that let os::elapsed_counter() use javaTimeNanos() which should be monotonic. I had to adjust also os::elapsed_frequency() and os::elapsedTime() to be consistent.

Bug: https://bugs.openjdk.java.net/browse/JDK-8231457
Webrev: http://cr.openjdk.java.net/~azeller/webrevs/8231457_2/

I will need a sponsor for this patch.

Best regards,
Arno