RFR: Avoid divide by zero error, improve variable names

[Y. Srinivas Ramakrishna]

On Wed, 21 Dec 2022 22:19:13 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Depending on when the periodic thread runs the accounting task and how much CPU time the process receives, we may see a very small elapsed process time. Such a time should not be used to compute MMU.

Marked as reviewed by ysr (Author).

src/hotspot/share/gc/shenandoah/shenandoahMmuTracker.cpp line 97:

> 95:   double process_time_s = process_time_seconds();
> 96:   double elapsed_process_time_s = process_time_s - _process_reference_time_s;
> 97:   if (elapsed_process_time_s <= 0.01) {

Is there a different mechanism one could use to check if there was an update? E.g. a change in the count of GC cycles started or ended, rather than relying on the magnitude of the difference, although the magnitude of the difference may still be sufficient. One related question: is this unit "seconds" or some smaller unit? The `_s` implies it's a second and 0.01 s is 10 ms which is not insubstantial...

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PR: https://git.openjdk.org/shenandoah/pull/188