RFR 6523160: RuntimeMXBean.getUptime() returns negative values

[David Holmes]

Jaroslav,

On 2/10/2013 6:47 PM, Jaroslav Bachorik wrote:
> 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.

Maybe I'm missing something but TiumeStamp updates using 
os::elapsed_counter() which on Linux uses gettimeofday so is not a 
monotonic clock source.

David
-----



> 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-