Run subprocess-starting tests on separate runners #30278
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I suspect that we are running out of process IDs, or the scheduler is not letting all subprocesses execute, leading to timeouts in tests that start subprocesses when other long-running tests are executing. This happens often with Python 3.14 tests for some reason. Add a new pytest marker for the tests that start a subprocess at top level, and run these tests in separate runners without pytest-xdist parallelization.
- set PYTHONUNBUFFERED=1 to make the subprocess Python unbuffered - set bufsize=0 making the parent process pipe unbuffered - because that can return short reads, check if the subprocess exited, and if not, yield the CPU - set stdin to DEVNULL and stderr to STDOUT to avoid blocking related to those
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I suspect that we are running out of process IDs, or the scheduler
is not letting all subprocesses execute, leading to timeouts in
tests that start subprocesses when other long-running tests are
executing. This happens often with Python 3.14 tests for some reason.
Add a new pytest marker for the tests that start a subprocess at
top level, and run these tests in separate runners without
pytest-xdist parallelization.