fix: improve telemetry worker stderr cleanup#3648
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Replace setImmediate + destroy() with process.stderr.end() callback to ensure all buffered writes are flushed before exiting. Add fallback exit in finally block to prevent worker from hanging if end() fails. This properly releases the inherited stderr file descriptor in debug mode, preventing the parent process from being blocked.
eablack
changed the title
Only call process.stderr.end() when DEBUG env var is set, mirroring the parent process logic where stderr is inherited only in DEBUG mode. When stderr is ignored, closing it is unnecessary and could cause issues.
k80bowman
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Apr 7, 2026
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k80bowman
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Thanks for continuing to iterate on this!
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Summary
Improved the telemetry worker's exit logic to properly flush stderr before exiting. The previous implementation used
setImmediate()+process.stderr.destroy(), which did not guarantee that buffered writes were flushed, potentially causing debug messages to be lost and the parent process to hang when stderr is inherited in DEBUG mode.The new implementation:
process.stderr.end()with a callback to ensure all buffered data is flushed before exitsetImmediate()in a finally block to prevent the worker from hanging ifend()failsType of Change
Patch Updates (patch semver update)
Testing
Notes:
This change affects the telemetry worker process that runs in the background when DEBUG mode is enabled. The issue would manifest as the parent CLI process hanging or debug messages being truncated.
Steps:
DEBUG=heroku:analyticsto verify telemetry worker exits cleanly