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.

src/hotspot/share/gc/shenandoah/shenandoahMmuTracker.cpp line 106:

> 104:   double elapsed_collector_time_s = collector_time_s - _collector_reference_time_s;
> 105:   _collector_reference_time_s = collector_time_s;
> 106:   double minimum_mutator_utilization = ((elapsed_process_time_s - elapsed_collector_time_s) / elapsed_process_time_s) * 100;

Alternative: You could check if result `isnan()` and not use it, although I don't know if divide by zero is costly.

-------------

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