RFR: 8284686: Interval of < 1 ms disables ExecutionSample events

[Jaroslav Bachorik]

On Mon, 11 Apr 2022 16:53:08 GMT, Johannes Bechberger <duke at openjdk.java.net> wrote:

> Fixes the issue by rounding the period interval to the next full millisecond larger than zero.
> 
> The following from the bug report works now:
> 
> java -XX:StartFlightRecording=filename=flight.jfr,jdk.ExecutionSample#period=999us CLASS_FILE; jfr print --events jdk.ExecutionSample flight.jfr
> 
> It considers the period to be `1ms`, producing the recording as expected.

src/jdk.jfr/share/classes/jdk/jfr/internal/settings/PeriodSetting.java line 118:

> 116:             long nanos = Utils.parseTimespanWithInfinity(value);
> 117:             if (nanos != Long.MAX_VALUE) {
> 118:                 eventType.setPeriod(Math.max(1, Math.round(nanos / 1_000_000f)), false, false);

Is `Math.round()` necessary here? 
We can just keep the integer division which will result to `0` for all arguments < 1_000_000 and the `Math.max()` will take care of providing the correct default.

Another thing to consider - what should happen if the `nanos` value is indeed `0`. Should the event perhaps be disabled?

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PR: https://git.openjdk.java.net/jdk/pull/8183