Sync instrument stress test

[jack-berg]

I'm doing some work to improve the performance of metric recording under high contention, and touching sensitive code in DefaultSynchronousMetricStorage and other concurrent code.

I have promising results, but the first step is buffing up our stress tests for synchronous instruments.

A stress test for synchronous instruments concurrently runs record and collect operations at a high rate, and tries to find instances of concurrency bugs: lost writes, duplicate writes, partial writes, etc.

We need to test every combination of of the following dimensions, since each plays a key role in the recording and collecting code flows.

• instrument type (counter, up down counter, explicit histogram, expo histogram, gauge) = 5
• instrument value type (double, long) = 2
• memory mode (reusuable, immutable) = 2
• aggregation temporality (cumulative, delta) = 2

That's 40 combinations. Our current test suite is hand rolled for some of these cases, but misses many.

[jack-berg]

Parameterized testing really shines here.

[jack-berg]

This is the key bit. We independently compute the expected aggregated state outside the concurrent record environment, and compare against the SDK, treating it as a black box.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.16%. Comparing base (d6ad3ae) to head (934ffcf).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7986   +/-   ##
=========================================
  Coverage     90.16%   90.16%           
  Complexity     7478     7478           
=========================================
  Files           836      834    -2     
  Lines         22550    22540   -10     
  Branches       2224     2236   +12     
=========================================
- Hits          20333    20324    -9     
+ Misses         1515     1512    -3     
- Partials        702      704    +2     

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[zeitlinger]

Looks good! I've asked Copilot for an additional review.

[Copilot]

Pull request overview

Adds a comprehensive stress test for synchronous metric instruments to exercise record/collect concurrency across all key configuration combinations, while removing older ad-hoc stress tests.

Changes:

• Introduces a new parameterized synchronous-instrument stress test spanning temporality, instrument type/aggregation, memory mode, and value type combinations.
• Removes legacy stress/stochastic concurrency tests spread across multiple unit test classes.
• Deletes the now-unused StressTestRunner utility.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/state/SynchronousMetricStorageTest.java	Removes the old concurrent record/collect stress test and related imports.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/aggregator/DoubleExplicitBucketHistogramAggregatorTest.java	Removes the multithreaded histogram update test and related imports.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SynchronousInstrumentStressTest.java	Adds a new parameterized stress test plus helpers to copy/reduce collected MetricData.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/StressTestRunner.java	Deletes the generic stress-test runner utility.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkLongUpDownCounterTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkLongHistogramTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkLongGaugeTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkLongCounterTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkDoubleUpDownCounterTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkDoubleHistogramTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkDoubleGaugeTest.java	Removes instrument-specific stress tests that used StressTestRunner.
sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/SdkDoubleCounterTest.java	Removes instrument-specific stress tests that used StressTestRunner.

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