[Exporter.Geneva] Avoid allocation for serializing scopes

[utpilla]

Changes

• Avoid allocation for serializing scopes

• Appropriate CHANGELOG.md updated for non-trivial changes

Benchmark Results:

main branch:

Method	Mean	Error	StdDev	Gen0	Allocated
SerializeLogRecord	660.2 ns	6.22 ns	5.82 ns	0.0162	104 B
Export	694.2 ns	2.49 ns	2.21 ns	0.0162	104 B

With this PR:

Method	Mean	Error	StdDev	Gen0	Allocated
SerializeLogRecord	582.3 ns	0.81 ns	0.72 ns	-	-
Export	646.0 ns	1.10 ns	0.86 ns	-	-

[CodeBlanch]

nit: m_exporterStateForScopes to be consistent with the other fields.

[utpilla]

Updated. I think we should update the field names to use Pascal case instead though. 😄

[CodeBlanch]

nit: Just reading the diff, it doesn't seem like ExporterStateForScopes is needed. You could do something more or less like this...

class MsgPackLogExporter
{
    private readonly ThreadLocal<SerializationDataForScopes> m_serializationData = new(() => null);

    private static readonly Action<LogRecordScope, MsgPackLogExporter> ProcessScopeForIndividualColumns = (scope, state) =>
    {
        var stateData = state.m_serializationData.Value;
        var customFields = state.m_customFields;

        // Do work
    }
}

Basically use MsgPackLogExporter as the state type.

[utpilla]

Great suggestion! Updated.

[codecov]

Codecov Report

Merging #818 (cf0c5bd) into main (3768220) will increase coverage by 0.35%.
The diff coverage is 61.65%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #818      +/-   ##
==========================================
+ Coverage   77.55%   77.90%   +0.35%     
==========================================
  Files         168      178      +10     
  Lines        5243     5459     +216     
==========================================
+ Hits         4066     4253     +187     
- Misses       1177     1206      +29     

Impacted Files	Coverage Δ
...stana/Implementation/InstanaExporterEventSource.cs	0.00% <0.00%> (ø)
...er.Instana/Implementation/InstanaSpanSerializer.cs	89.62% <0.00%> (-4.17%)	⬇️
...metry.Exporter.Instana/Implementation/Transport.cs	18.29% <0.00%> (-2.76%)	⬇️
...ry.Exporter.Geneva/Metrics/GenevaMetricExporter.cs	58.49% <100.00%> (+0.39%)	⬆️
...orter.Geneva/MsgPackExporter/MsgPackLogExporter.cs	94.19% <100.00%> (+1.55%)	⬆️
...ter.Geneva/MsgPackExporter/MsgPackTraceExporter.cs	92.92% <100.00%> (+0.03%)	⬆️
...etry.Exporter.Instana/Implementation/SpanSender.cs	61.53% <100.00%> (ø)
...Implementation/AspNetInstrumentationEventSource.cs	76.92% <0.00%> (ø)
...ry.Instrumentation.AspNet/AspNetInstrumentation.cs	100.00% <0.00%> (ø)
... and 9 more