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Log exceptions that end a thread - #53

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thomas-samoht merged 1 commit into
fix/endpoint-route-templatefrom
feat/log-unhandled-thread-exceptions
Nov 10, 2026
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thomas-samoht merged 1 commit into
fix/endpoint-route-templatefrom
feat/log-unhandled-thread-exceptions

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install_excepthook() only replaced sys.excepthook, which Python calls only for the main thread. When an exception ended any other thread, such as a background worker or a thread pool task, Python's default threading.excepthook printed the traceback to stderr. That output went through no stream, so nothing on the log server showed that the work had stopped.

install_excepthook() now also installs threading.excepthook. It logs SYS_UNHANDLED_EXCEPTION with the thread name, exception_type and the traceback. The process keeps running after a thread ends, so this is not logged as SYS_APP_CRASHED and the shutdown reason stays unchanged. SystemExit is ignored, just as the default hook ignores it.

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thomas-samoht marked this pull request as ready for review November 5, 2026 09:05
@thomas-samoht
thomas-samoht requested a review from a team as a code owner November 5, 2026 09:05
ricklambrechts
ricklambrechts previously approved these changes Nov 9, 2026
@thomas-samoht
thomas-samoht force-pushed the feat/log-unhandled-thread-exceptions branch from 38563ee to eb82429 Compare November 9, 2026 15:57
@thomas-samoht
thomas-samoht changed the base branch from main to fix/endpoint-route-template November 9, 2026 15:57
@thomas-samoht
thomas-samoht added this pull request to stack #61 November 9, 2026 15:57
ricklambrechts
ricklambrechts previously approved these changes Nov 9, 2026
@thomas-samoht
thomas-samoht dismissed ricklambrechts’s stale review November 10, 2026 08:51

The merge-base changed after approval.

@thomas-samoht
thomas-samoht force-pushed the feat/log-unhandled-thread-exceptions branch 6 times, most recently from 5c5800e to 5cbe8b3 Compare November 10, 2026 09:14
Problem: install_excepthook() only replaced sys.excepthook, which Python
calls for the main thread. An exception that ended any other thread,
such as a background worker or a thread pool task, went through
threading.excepthook instead, whose default prints the traceback to
stderr. It never reached a stream, and nothing on the log server showed
that the work had stopped.

Fix: install_excepthook() also installs threading.excepthook. It logs
SYS_UNHANDLED_EXCEPTION with the exception type, the thread name in the
message and the traceback, on the catalogue the excepthook uses. The
process keeps running after a thread ends, so it is not logged as
SYS_APP_CRASHED and the shutdown reason stays as it was. SystemExit is
left alone, as the default hook does. The guide mentions the new
coverage.
@thomas-samoht
thomas-samoht force-pushed the feat/log-unhandled-thread-exceptions branch from 5cbe8b3 to b850034 Compare November 10, 2026 09:16
@thomas-samoht
thomas-samoht merged commit ed82914 into main Nov 10, 2026
14 checks passed
@thomas-samoht
thomas-samoht deleted the feat/log-unhandled-thread-exceptions branch November 10, 2026 09:19
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2 participants