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After upgrading my first macOS system to the newly released macOS 10.14.4 update, attempts to run the Python test suite via regrtest fail:
$ /usr/local/bin/python3.7 -m test -uall -j3 -w
Traceback (most recent call last):
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 193, in _run_module_as_main
 "__main__", mod_spec)
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 85, in _run_code
 exec(code, run_globals)
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/test/__main__.py", line 2, in <module>
 main()
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/test/libregrtest/main.py", line 640, in main
 Regrtest().main(tests=tests, **kwargs)
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/test/libregrtest/main.py", line 586, in main
 self._main(tests, kwargs)
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/test/libregrtest/main.py", line 607, in _main
 setup_tests(self.ns)
 File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/test/libregrtest/setup.py", line 77, in setup_tests
 resource.setrlimit(resource.RLIMIT_STACK, (newsoft, hard))
ValueError: current limit exceeds maximum limit
The error is during regrtest initialization when it is trying to increase the process stack size to avoid previously seen problems when running tests. This code has been unchanged for a long time.
Stepping through the code in the REPL on 10.14.4:
>>> import resource
>>> resource.getrlimit(resource.RLIMIT_STACK)
(8388608, 67104768)
>>> soft, hard = resource.getrlimit(resource.RLIMIT_STACK)
>>> newsoft = min(hard, max(soft, 1024*2048))
>>> newsoft
8388608
>>> resource.setrlimit(resource.RLIMIT_STACK, (newsoft, hard))
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
ValueError: current limit exceeds maximum limit
The same code run on a macOS system still running 10.14.3 gives the same values from getrlimit but does not fail when calling setrlimit.
I will investigate further tomorrow; if this is a general problem with macOS 10.14.4, we'll need to provide a workaround and possibly open an incident report with Apple.