PrometheusExporter for MP metrics conversion error

[larslorenzen]

Description

---

When exporting metrics of a rest method annotated with @Timed, some of the values are zero because of a conversion bug.

These conversion values:

    private static final double NANOSECOND_CONVERSION = 1 / 1_000_000_000;
    private static final double MICROSECOND_CONVERSION = 1 / 1_000_000;
    private static final double MILLISECOND_CONVERSION = 1 / 1_000;

all convert to zero and therefore @Timed quantiles are 0.
The conversion to double is done after the integer division so all 3 conversion values are 0.0d.

Expected Outcome

Correct conversion is done for the timer metrics samples exported in prometheus format.

Current Outcome

All reported quantiles are 0.

Steps to reproduce (Only for bug reports)

Create a rest resource with a @Timed annotated method and call that method a few times.
Then observe /metrics in prometheus format.

Samples

application:de_llorenzen_resource_accept_seconds{quantile="0.5"} 0.0
application:de_llorenzen_resource_accept_seconds{quantile="0.75"} 0.0
application:de_llorenzen_resource_accept_seconds{quantile="0.95"} 0.0
application:de_llorenzen_resource_accept_seconds{quantile="0.98"} 0.0
application:de_llorenzen_resource_accept_seconds{quantile="0.99"} 0.0
application:de_llorenzen_resource_accept_seconds{quantile="0.999"} 0.0

Context (Optional)

fish.payara.microprofile.metrics.writer.PrometheusExporter

Environment

• Payara Version: 5.181, 5.182
• Edition: All
• JDK Version: 8 Oracle
• Operating System: Linux / Mac