Issue 8831 exporter backpressure

[codedbyadiiii]

Summary

Adds an opt-in mechanism for exporters to signal their supported export concurrency.

Changes

• Adds getConcurrencyLimit() to span, log, and metric exporter interfaces.
• Preserves serialized export behavior by default.
• Adds bounded concurrent export execution to:
  • BatchSpanProcessor
  • BatchLogRecordProcessor
  • PeriodicMetricReader
• Uses caller-runs backpressure when exporter capacity is exhausted.
• Ensures in-flight exports complete during flush and shutdown.
• Adds regression coverage for concurrent span exports.
• Updates generated API-diff files.

Testing

• ./gradlew :sdk:trace:test :sdk:logs:test :sdk:metrics:test
• ./gradlew :sdk:trace:jApiCmp :sdk:logs:jApiCmp :sdk:metrics:jApiCmp

[otelbot]

⚠️ API changes detected — additional maintainer review required

@jack-berg @jkwatson

This PR modifies the public API surface area of the following module(s):

• opentelemetry-sdk-logs
• opentelemetry-sdk-metrics
• opentelemetry-sdk-trace

Please review the changes in docs/apidiffs/current_vs_latest/ carefully before approving.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on reviewers · refreshed 2026-10-12 18:18 UTC

Review the latest changes.

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[codecov]

Codecov Report

❌ Patch coverage is 79.50820% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.61%. Comparing base (387f5c5) to head (1df6a6c).

Files with missing lines	Patch %	Lines
...metry/sdk/logs/export/BatchLogRecordProcessor.java	74.41%	10 Missing and 1 partial ⚠️
...telemetry/sdk/trace/export/BatchSpanProcessor.java	81.81%	8 Missing ⚠️
...metry/sdk/metrics/export/PeriodicMetricReader.java	81.25%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (79.50%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8928      +/-   ##
============================================
- Coverage     90.65%   90.61%   -0.05%     
- Complexity    10887    10894       +7     
============================================
  Files          1015     1015              
  Lines         29731    29847     +116     
  Branches       3876     3892      +16     
============================================
+ Hits          26953    27045      +92     
- Misses         1860     1884      +24     
  Partials        918      918              

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