Leverage ActivityListener.AutoGenerateRootContextTraceId

[cijothomas]

Fixes portions of #941 #953

Changes

Leverage ActivityListener.AutoGenerateRootContextTraceId so that sampling callbacks can get the actual TraceId of the to-be-created Activity and make decision based on TraceId.
Before this PR, Samplers generated a random TraceId, and made sampling decision. But this generated TraceID was not actually used when the Activity is created, leading to broken traces, if samplers made decision based on the TraceId.

Added Tests. There are TODOs which require follow up.

Please provide a brief description of the changes here. Update the
CHANGELOG.md for non-trivial changes.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1007 into master will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1007      +/-   ##
==========================================
- Coverage   68.91%   68.86%   -0.06%     
==========================================
  Files         220      220              
  Lines        5999     5999              
  Branches      984      983       -1     
==========================================
- Hits         4134     4131       -3     
- Misses       1596     1599       +3     
  Partials      269      269              

Impacted Files	Coverage Δ
src/OpenTelemetry/Sdk.cs	89.28% <100.00%> (+1.19%)	⬆️
src/OpenTelemetry/Metrics/CounterMetricSdkBase.cs	80.00% <0.00%> (-13.34%)	⬇️

[reyang]

I guess we need an empty line here.

[cijothomas]

Your favourite tool caught it as well!

[CodeBlanch]

🚨

[alanwest]

Just want to clarify my understanding, next OTel release will coincide with preview 8. So, will preview 8 will not contain the removal of AutoGenerateRootContextTraceId? Or is this just getting the functionality/tests in place and then the plan is to change this prior to release?

[cijothomas]

Just want to clarify my understanding, next OTel release will coincide with preview 8. So, will preview 8 will not contain the removal of AutoGenerateRootContextTraceId? Or is this just getting the functionality/tests in place and then the plan is to change this prior to release?

Preview8 won't remove AutoGenerateRootContextTraceId. It'll be RC1 or RC2.

[CodeBlanch]

@cijothomas @reyang Hey I just noticed something, this broke the ParentOrElse sampler.

            var parentContext = samplingParameters.ParentContext;
            if (parentContext == default)

parentContext == default will now never be true, because a TraceId is always generated. Not sure how to detect "no parent" case now. Check SpanId = all 0s?