feat(trace): support runtime sampler updates

[abhiramaab]

Summary

Add runtime sampler updates to SdkTracerProvider so a sampler can be changed after the provider is built.

Changes

• Add SdkTracerProvider.setSampler(Sampler)
• Make the shared sampler reference mutable so new spans observe updates
• Add tests for:
  • updating the sampler at runtime
  • null rejection
  • an existing tracer observing the new sampler for new spans

Verification

• ./gradlew :sdk:trace:test --tests io.opentelemetry.sdk.trace.SdkTracerProviderTest
• ./gradlew :sdk:trace:test
• ./gradlew spotlessApply
• git diff --check

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: abhiramaab / name: abhiramaab (213ffb5)

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Waiting on the author · refreshed 2026-08-10 12:23 UTC

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[Copilot]

Pull request overview

This PR adds support for updating the SdkTracerProvider sampler at runtime so that new spans (including those created from previously obtained Tracer instances) observe the updated sampler.

Changes:

• Introduces SdkTracerProvider.setSampler(Sampler) and corresponding test coverage for runtime updates and null rejection.
• Makes the shared sampler reference mutable (volatile) so new span creation uses the latest sampler.
• Adds a test verifying sampler updates affect spans started from an existing Tracer.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
sdk/trace/src/main/java/io/opentelemetry/sdk/trace/SdkTracerProvider.java	Adds public runtime sampler setter and keeps sampler accessible via getSampler().
sdk/trace/src/main/java/io/opentelemetry/sdk/trace/TracerSharedState.java	Makes sampler mutable to allow runtime updates for span creation.
sdk/trace/src/test/java/io/opentelemetry/sdk/trace/SdkTracerProviderTest.java	Adds tests for sampler updates, null rejection, and existing tracer behavior.

Suppressed comments (1)

sdk/trace/src/main/java/io/opentelemetry/sdk/trace/SdkTracerProvider.java:125

• getSampler() now returns the current sampler (it can change at runtime), but its Javadoc still says "configured" which reads like an immutable build-time value.

  /** Returns the configured {@link Sampler}. */
  public Sampler getSampler() {
    return sharedState.getSampler();
  }

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[abhiramaab]

Follow-up: added sampler lifecycle handling so replaced samplers are shut down, and samplers set after provider shutdown are immediately shut down. Added tests covering both cases. :sdk:trace:test passes.