[sdk] Expose the ctor on Batch<T> which accepts a single item

[CodeBlanch]

To help resolve: open-telemetry/opentelemetry-dotnet-contrib#1814

Changes

• Expose the ctor on Batch<T> which accepts a single item for the batch.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.61%. Comparing base (6250307) to head (8c02916).
Report is 372 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5642      +/-   ##
==========================================
+ Coverage   83.38%   86.61%   +3.22%     
==========================================
  Files         297      262      -35     
  Lines       12531    11804     -727     
==========================================
- Hits        10449    10224     -225     
+ Misses       2082     1580     -502     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.58% <100.00%> (?)
unittests-Project-Stable	86.54% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/Batch.cs	96.18% <100.00%> (-1.36%)	⬇️

... and 241 files with indirect coverage changes

[CodeBlanch]

@reyang is going to explore doing something with attributes to allow users to opt-into having SimpleExportProcessor switch into a reentrant/non-blocking mode. Going to keep this in draft to give him time to investigate that and then we can decide which direction to take.

[reyang]

I have a different idea how to solve this (and a category of similar problems), check #5643.

[github-actions]

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[github-actions]

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[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[CodeBlanch]

Re-opening this PR.

There are some good alternative proposals in #5643 and #5758 however @alanwest and I feel we need to wait for the spec to prescribe what to do before moving forward: open-telemetry/opentelemetry-specification#4231 (comment).

We have decided to expose this ctor in the meantime to unblock users.

The spec says SDK MUST allow users to implement and configure custom processors. What GenevaExporter wants to do (open-telemetry/opentelemetry-dotnet-contrib#1814) is make a custom processor which exports a single item and does not block. Having this ctor makes it possible to implement that in a safe and efficient way. The SDK shouldn't block this valid scenario from being supported/successful.

When the spec defines a concurrent simple processor it will be supported. But users should still be able to make custom implementations whatever they may be regardless.

[cijothomas]

Thanks!