refactor(tracer): add checklocks annotations to Span struct

[kakkoyun]

Add compile-time lock verification annotations to the Span struct,
the most critical data structure in the tracing library.

Signed-off-by: Kemal Akkoyun kemal.akkoyun@datadoghq.com

What does this PR do?

Motivation

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[codecov]

Codecov Report

❌ Patch coverage is 93.22034% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.42%. Comparing base (4557cb1) to head (5195a97).

Files with missing lines	Patch %	Lines
ddtrace/tracer/span.go	90.24%	2 Missing and 2 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/abandonedspans.go	90.64% <ø> (ø)
ddtrace/tracer/civisibility_tslv.go	25.51% <ø> (ø)
ddtrace/tracer/context.go	61.90% <ø> (ø)
ddtrace/tracer/payload_v1.go	63.05% <ø> (ø)
ddtrace/tracer/rules_sampler.go	83.29% <100.00%> (ø)
ddtrace/tracer/sampler.go	93.67% <ø> (ø)
ddtrace/tracer/span_msgp.go	32.27% <ø> (ø)
ddtrace/tracer/spancontext.go	88.29% <100.00%> (ø)
ddtrace/tracer/stats.go	98.41% <ø> (ø)
ddtrace/tracer/textmap.go	84.04% <100.00%> (ø)
... and 3 more

... and 355 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-02-21 10:10:07

Comparing candidate commit 98c75e2 in PR branch kakkoyun/LANGPLAT-434/add_checklocks_for_span with baseline commit 69beee1 in branch main.

Found 7 performance improvements and 0 performance regressions! Performance is the same for 149 metrics, 8 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:BenchmarkHttpServeTrace-25

• 🟩 execution_time [-399.914ns; -354.286ns] or [-3.491%; -3.093%]

scenario:BenchmarkSetTagMetric-25

• 🟩 execution_time [-13.632ns; -13.022ns] or [-18.665%; -17.830%]

scenario:BenchmarkSetTagString-25

• 🟩 execution_time [-10.908ns; -10.292ns] or [-15.639%; -14.755%]

scenario:BenchmarkSetTagStringPtr-25

• 🟩 execution_time [-13.170ns; -12.180ns] or [-13.969%; -12.918%]

scenario:BenchmarkSetTagStringer-25

• 🟩 execution_time [-11.983ns; -10.819ns] or [-15.615%; -14.099%]

scenario:BenchmarkStartSpanConfig/scenario_WithStartSpanConfig-25

• 🟩 execution_time [-144.531ns; -133.069ns] or [-5.310%; -4.889%]

scenario:BenchmarkStartSpanConfig/scenario_none-25

• 🟩 execution_time [-153.033ns; -142.567ns] or [-5.362%; -4.995%]

[kakkoyun]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[kakkoyun]

Benchmarks

Benchmark execution time: 2026-02-19 11:17:52

Comparing candidate commit 4ae27e0 in PR branch kakkoyun/LANGPLAT-434/add_checklocks_for_span with baseline commit a39a21d in branch main.

Found 7 performance improvements and 0 performance regressions! Performance is the same for 147 metrics, 10 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

scenario:BenchmarkHttpServeTrace-25

• 🟩 execution_time [-373.924ns; -334.876ns] or [-3.272%; -2.930%]

scenario:BenchmarkSetTagMetric-25

• 🟩 execution_time [-14.582ns; -13.488ns] or [-19.786%; -18.302%]

scenario:BenchmarkSetTagString-25

• 🟩 execution_time [-11.256ns; -10.590ns] or [-16.144%; -15.189%]

scenario:BenchmarkSetTagStringPtr-25

• 🟩 execution_time [-13.948ns; -12.062ns] or [-14.807%; -12.804%]

scenario:BenchmarkSetTagStringer-25

• 🟩 execution_time [-11.579ns; -10.555ns] or [-15.176%; -13.834%]

scenario:BenchmarkStartSpanConfig/scenario_WithStartSpanConfig-25

• 🟩 execution_time [-145.849ns; -129.951ns] or [-5.320%; -4.740%]

scenario:BenchmarkStartSpanConfig/scenario_none-25

• 🟩 execution_time [-154.111ns; -137.089ns] or [-5.363%; -4.770%]

This is probably the result of eliminating some closures. checklocks gets confused by them. However, nice side effect.

[darccio]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 9c86d36006

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[codecov]

Codecov Report

❌ Patch coverage is 93.22034% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.54%. Comparing base (4557cb1) to head (5195a97).

Files with missing lines	Patch %	Lines
ddtrace/tracer/span.go	90.24%	2 Missing and 2 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/abandonedspans.go	90.64% <ø> (ø)
ddtrace/tracer/civisibility_tslv.go	25.51% <ø> (ø)
ddtrace/tracer/context.go	61.90% <ø> (ø)
ddtrace/tracer/payload_v1.go	63.05% <ø> (ø)
ddtrace/tracer/rules_sampler.go	83.29% <100.00%> (ø)
ddtrace/tracer/sampler.go	93.67% <ø> (ø)
ddtrace/tracer/span_msgp.go	32.27% <ø> (ø)
ddtrace/tracer/spancontext.go	88.29% <100.00%> (ø)
ddtrace/tracer/stats.go	98.41% <ø> (ø)
ddtrace/tracer/textmap.go	84.04% <100.00%> (ø)
... and 3 more

... and 357 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[codecov]

Codecov Report

❌ Patch coverage is 93.22034% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.67%. Comparing base (69beee1) to head (98c75e2).

Files with missing lines	Patch %	Lines
ddtrace/tracer/span.go	90.24%	2 Missing and 2 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/abandonedspans.go	90.64% <ø> (ø)
ddtrace/tracer/civisibility_tslv.go	25.51% <ø> (ø)
ddtrace/tracer/context.go	61.90% <ø> (ø)
ddtrace/tracer/payload_v1.go	63.05% <ø> (ø)
ddtrace/tracer/rules_sampler.go	83.29% <100.00%> (-0.28%)	⬇️
ddtrace/tracer/sampler.go	93.67% <ø> (ø)
ddtrace/tracer/span_msgp.go	32.27% <ø> (ø)
ddtrace/tracer/spancontext.go	88.29% <100.00%> (+0.05%)	⬆️
ddtrace/tracer/stats.go	98.41% <ø> (ø)
ddtrace/tracer/textmap.go	84.04% <100.00%> (ø)
... and 3 more

... and 3 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[datadog-datadog-prod-us1-2]

⚠️ Tests

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

❄️ 1 New flaky test detected

TestStopLatency from github.com/DataDog/dd-trace-go/v2/profiler (Datadog) (Fix with Cursor)

Failed

=== RUN   TestStopLatency
    profiler_test.go:251: profiler took 502.49ms to stop
--- FAIL: TestStopLatency (1.58s)

ℹ️ Info

🧪 All tests passed

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 98c75e2 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}