tests/conftest: fix concurrent access to pexpect.spawn#1937
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Bastian-Krause merged 1 commit intoJul 16, 2026
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pexpect/ptyprocess are not thread-safe. But we need a thread to keep reading the Exporter/Coordinator outputs during the tests for debugging purposes. The reader thread (calling `pexpect.spawn.read_nonblocking()`) and the main thread (calling `pexpect.spawn`'s `kill()`/`wait()`/`isalive()`) can access it concurrently. Internally, pexpect calls waitpid(2) in these methods. This behavior leads to errors such as: ptyprocess.util.PtyProcessError: isalive() encountered condition where "terminated" is 0, but there was no child process. Did someone else call waitpid() on our process? Or: pexpect.exceptions.ExceptionPexpect: isalive() encountered condition where "terminated" is 0, but there was no child process. Did someone else call waitpid() on our process? Fix this by serializing access to pexpect.spawn through a lock. Signed-off-by: Bastian Krause <bst@pengutronix.de>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #1937 +/- ##
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- Coverage 61.0% 61.0% -0.1%
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Files 182 182
Lines 14881 14881
========================================
- Hits 9083 9081 -2
- Misses 5798 5800 +2
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Bastian-Krause
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Jul 15, 2026
Bastian-Krause
merged commit Jul 16, 2026
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Description
Another deep dive into our flaky CI tests:
pexpect/ptyprocess are not thread-safe. But we need a thread to keep reading the Exporter/Coordinator outputs during the tests for debugging purposes.
The reader thread (calling
pexpect.spawn.read_nonblocking()) and the main thread (callingpexpect.spawn'skill()/wait()/isalive()) can access it concurrently. Internally, pexpect calls waitpid(2) in these methods.This behavior leads to errors such as:
Or:
These errors pop up in CI from time to time: https://github.com/labgrid-project/labgrid/actions/runs/29324126371/job/87056209839
Fix this by serializing access to
pexpect.spawnthrough a lock.Checklist
Fixes #547