[OpenBSD], [NetBSD] Process cwd() can raise FileNotFoundError

[giampaolo]

Summary

• OS: OpenBSD, NetBSD
• Type: core

Description

Observed in unit tests:

======================================================================
ERROR: psutil.tests.test_contracts.TestFetchAllProcesses.test_all
----------------------------------------------------------------------
multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "/vagrant/psutil/psutil/tests/test_contracts.py", line 389, in proc_info
    info[fun_name] = fun()
  File "/vagrant/psutil/psutil/__init__.py", line 719, in cwd
    return self._proc.cwd()
  File "/vagrant/psutil/psutil/_psbsd.py", line 566, in wrapper
    return fun(self, *args, **kwargs)
  File "/vagrant/psutil/psutil/_psbsd.py", line 842, in cwd
    return cext.proc_cwd(self.pid) or None
FileNotFoundError: [Errno 2] No such file or directory
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/vagrant/psutil/psutil/tests/test_contracts.py", line 431, in test_all
    for info in self.iter_proc_info():
  File "/usr/local/lib/python3.8/multiprocessing/pool.py", line 868, in next
    raise value
FileNotFoundError: [Errno 2] No such file or directory

Also reproducible with:

import psutil

for p in psutil.process_iter():
    print(p)
    try:
        print(p.cwd())
    except psutil.AccessDenied:
        print("AD")

...which prints:

psutil.Process(pid=63428, name='bash', status='sleeping', started='15:30:39')
Traceback (most recent call last):
  File "foo.py", line 6, in <module>
    print(p.cwd())
  File "/vagrant/psutil/psutil/__init__.py", line 719, in cwd
    return self._proc.cwd()
  File "/vagrant/psutil/psutil/_psbsd.py", line 566, in wrapper
    return fun(self, *args, **kwargs)
  File "/vagrant/psutil/psutil/_psbsd.py", line 842, in cwd
    return cext.proc_cwd(self.pid) or None
FileNotFoundError: [Errno 2] No such file or directory

Not sure why this happens. Probably the directory was deleted and internally the kernel calls stat() against it. Regardless, it should not crash with FileNotFoundError. Even though not documented, there are circumstances where we return None if cwd() cannot be determined (BSD*, AIX, SunOS), so we should do the same here.

EDIT: despite not directly cached in unit tests, the same problem can also occur on NetBSD.