Add thread details for declarative config via span processor

[trask]

Adds support for the experimental thread.id / thread.name span attributes under declarative configuration, for both the javaagent and the spring starter.

Rather than an InstrumenterCustomizer / AttributesExtractor, this registers the existing ThreadDetailsSpanProcessor via declarative config (a named ComponentProvider plus a DeclarativeConfigurationCustomizerProvider that injects the processor node when enabled). Because it stays a SpanProcessor, the attributes are added to manually-created spans too, not only Instrumenter-built spans.

• agent: enabled via the distribution.javaagent.thread_details_enabled declarative-config node (the legacy otel.javaagent.add-thread-details property is still honored via non-declarative ConfigProperties)
• spring starter: enabled via distribution.spring_starter.thread_details_enabled

Alternative to the InstrumenterCustomizer/AttributesExtractor approach in #15209.

Resolves #14087.

[Copilot]

Pull request overview

Adds declarative-config support for emitting experimental thread span attributes (thread.id, thread.name) by registering the existing AddThreadDetailsSpanProcessor through the declarative configuration component model. This enables thread attributes for both instrumentation-created spans and manually created spans, across the javaagent and Spring Boot starter.

Changes:

• Introduce a declarative-config ComponentProvider for AddThreadDetailsSpanProcessor and a reusable model customizer that injects it when enabled.
• Wire enablement for the javaagent via distribution.javaagent (backed by AgentDistributionConfig) and for the Spring starter via distribution.spring_starter.thread_details_enabled.
• Add/adjust tests and smoke-test config to validate Spring starter behavior and document the javaagent property behavior.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
smoke-tests-otel-starter/spring-boot-2/src/testDeclarativeConfig/resources/application.yaml	Enables thread details under distribution.spring_starter for declarative-config smoke testing.
smoke-tests-otel-starter/spring-boot-2/src/testDeclarativeConfig/java/io/opentelemetry/spring/smoketest/OtelSpringStarterSmokeTest.java	Asserts thread.id / thread.name are present in exported spans.
sdk-autoconfigure-support/src/main/resources/META-INF/services/io.opentelemetry.sdk.autoconfigure.spi.internal.ComponentProvider	Registers the new declarative-config ComponentProvider via SPI.
sdk-autoconfigure-support/src/main/java/io/opentelemetry/instrumentation/thread/internal/AddThreadDetailsComponentProvider.java	Exposes AddThreadDetailsSpanProcessor as a named declarative-config component (thread_details).
sdk-autoconfigure-support/src/main/java/io/opentelemetry/instrumentation/thread/internal/AbstractThreadDetailsCustomizerProvider.java	Injects the thread_details span processor model when enabled, avoiding duplicates.
javaagent-tooling/src/test/java/io/opentelemetry/javaagent/tooling/config/ThreadDetailsCustomizerProviderTest.java	Tests javaagent-side customizer behavior (commented on coverage of true declarative-config path).
javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/config/ThreadDetailsCustomizerProvider.java	Javaagent declarative-config customizer provider that enables thread details based on AgentDistributionConfig.
javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/AgentTracerProviderConfigurer.java	Uses AgentDistributionConfig to decide whether to install AddThreadDetailsSpanProcessor in non-DC mode.
javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/extension/instrumentation/internal/AgentDistributionConfig.java	Adds thread_details_enabled to distribution config and maps system-property defaulting behavior.
instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/instrumentation/thread/ThreadDetailsCustomizerProviderTest.java	Tests Spring starter declarative-config enablement parsing and injection behavior.
instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/OpenTelemetryAutoConfiguration.java	Registers the Spring starter declarative-config customizer bean.
instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/instrumentation/thread/ThreadDetailsCustomizerProvider.java	Spring starter provider that reads distribution.spring_starter.thread_details_enabled.
docs/advanced-configuration-options.md	Documents otel.javaagent.add-thread-details behavior and defaults.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

[Copilot]

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Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

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[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

[Copilot]

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Copilot reviewed 15 out of 15 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated no new comments.

[zeitlinger]

I’m good with this PR and will approve — as maintainer it’s your call which tradeoff to prefer.

If we ever want to have both:

• sampler visibility for thread.id / thread.name
• and coverage for manual spans

then I think there are two possible follow-up directions:

Option 1: hybrid

Do both:

• add thread.id / thread.name via an AttributesExtractor / instrumenter hook for Instrumenter-built spans
• keep the SpanProcessor as a fallback for manual spans
• make the SpanProcessor back off if those attributes are already present

That would let us have both for most practical cases:

• instrumented spans: sampler can see the attrs before span start
• manual spans: final span still gets the attrs

The only thing this still would not give us is sampler visibility for manual spans, since the sampler runs before the span processor.

Option 2: deeper work

If we want to fully have both — meaning:

• sampler-visible thread attrs
• and manual-span coverage
• and no behavior difference between instrumented vs manual spans

then I think this needs a deeper hook than a span processor:

• either teach the declarative/rule-based sampler to compute thread.name / thread.id directly from Thread.currentThread()
• or add some earlier SDK/start-span hook that can populate those values before sampling

So as I see it:

• this PR chooses manual-span parity
• the hybrid follow-up would let us have both for instrumented spans + final-span coverage for manual spans
• deeper sampler/SDK work is the only way to fully have both

References:

• sampler concern in declarative config: add thread details resource processor #14564: declarative config: add thread details resource processor #14564 (comment)
• instrumenter-based attempt in add thread details for declarative config #15209: add thread details for declarative config #15209
• reason for switching back in Add thread details for declarative config via span processor #19008: add thread details for declarative config #15209 (comment)