perf(config): cache sys getenv

[morrisonlevi]

Description

In request initialization aka rinit/activate, calling the system getenv when a SAPI env var isn't found is slow enough it shows up in profiles:

Note that glibc's getenv does a linear scan on the environ and does strncmp on the members, so we can definitely do better.

This is also arguably more correct: system environment variables map to a system INI setting, which shouldn't change at runtime.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-official]

⚠️ Tests

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

🧪 1028 Tests failed

testSearchPhpBinaries from integration.DDTrace\Tests\Integration\PHPInstallerTest (Datadog) (Fix with Cursor)

DDTrace\Tests\Integration\PHPInstallerTest::testSearchPhpBinaries
Test code or tested code printed unexpected output: Searching for available php binaries, this operation might take a while.

testSimplePushAndProcess from laravel-58-test.DDTrace\Tests\Integrations\Laravel\V5_8\QueueTest (Datadog) (Fix with Cursor)

DDTrace\Tests\Integrations\Laravel\V5_8\QueueTest::testSimplePushAndProcess
Test code or tested code printed unexpected output: spanLinksTraceId: 699ee8e500000000c3b90521ff071a26
tid: 699ee8e500000000
hexProcessTraceId: c3b90521ff071a26
hexProcessSpanId: b88f6e41af859e1c
processTraceId: 14103309351658134054
processSpanId: 13298969453045063196

phpvfscomposer://tests/vendor/phpunit/phpunit/phpunit:106

testSimplePushAndProcess from laravel-8x-test.DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest (Datadog) (Fix with Cursor)

DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest::testSimplePushAndProcess
Test code or tested code printed unexpected output: spanLinksTraceId: 699ee7680000000089cb7bd0e9c8e652
tid: 699ee76800000000
hexProcessTraceId: 89cb7bd0e9c8e652
hexProcessSpanId: 03c9e6fa682c9559
processTraceId: 9929165940674061906
processSpanId: 273003215596590425

View all

ℹ️ Info

❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: e26db1d | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.08%. Comparing base (25893da) to head (5a292ea).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3670   +/-   ##
=======================================
  Coverage   62.08%   62.08%           
=======================================
  Files         141      141           
  Lines       13352    13352           
  Branches     1746     1746           
=======================================
  Hits         8290     8290           
  Misses       4269     4269           
  Partials      793      793           

---

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[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-02-25 13:22:47

Comparing candidate commit e26db1d in PR branch levi/cache-getenv with baseline commit 07b618a in branch master.

Found 2 performance improvements and 6 performance regressions! Performance is the same for 186 metrics, 0 unstable metrics.

scenario:ComposerTelemetryBench/benchTelemetryParsing

• 🟥 execution_time [+0.862µs; +1.738µs] or [+7.559%; +15.248%]

scenario:HookBench/benchHookOverheadTraceMethod-opcache

• 🟥 execution_time [+3.551µs; +13.430µs] or [+2.047%; +7.743%]

scenario:MessagePackSerializationBench/benchMessagePackSerialization

• 🟩 execution_time [-10.760µs; -8.940µs] or [-9.767%; -8.115%]

scenario:MessagePackSerializationBench/benchMessagePackSerialization-opcache

• 🟩 execution_time [-9.814µs; -8.906µs] or [-8.814%; -7.999%]

scenario:SamplingRuleMatchingBench/benchRegexMatching1

• 🟥 execution_time [+99.665ns; +155.935ns] or [+8.657%; +13.544%]

scenario:SamplingRuleMatchingBench/benchRegexMatching2

• 🟥 execution_time [+113.060ns; +172.940ns] or [+9.848%; +15.064%]

scenario:SamplingRuleMatchingBench/benchRegexMatching3

• 🟥 execution_time [+111.600ns; +184.000ns] or [+9.596%; +15.821%]

scenario:SamplingRuleMatchingBench/benchRegexMatching4

• 🟥 execution_time [+113.780ns; +153.620ns] or [+9.918%; +13.391%]