RFR 6523160: RuntimeMXBean.getUptime() returns negative values

[Jaroslav Bachorik]

Hello,

currently the JVM uptime reported by the RuntimeMXBean is based on 
System.currentTimeMillis() which makes it susceptible to changes of the 
OS time (eg. changing timezone, NTP synchronization etc.). The uptime 
should not depend on the system time and should be calculated using a 
monotonic clock source.

There is already the way to get the actual JVM uptime in ticks. It is 
accessible as Management::timestamp() and the ticks are convertible to 
milliseconds using Management::ticks_to_ms(ts_ticks) thus making it very 
easy to switch to the monotonic clock based uptime.

The patch consists of the hotspot and jdk parts.

For the hotspot a new constant needs to be introduced in 
src/share/vm/services/jmm.h and the actual logic to obtain the uptime in 
milliseconds is added in src/share/vm/services/management.cpp.

For the jdk the changes comprise of adding the necessary JNI bridging 
methods in order to get the new uptime, introducing the same constant 
that is used in hotspot and changes to mapfile-vers files in order to 
properly build the native library.

Issue:   https://bugs.openjdk.java.net/browse/JDK-6523160
Webrev:  http://cr.openjdk.java.net/~jbachorik/6523160/webrev.00

Thanks,

-JB-