[Windows] `pid_exists()` and `Process()` disagree on whether a pid exists when ERROR_ACCESS_DENIED about psutil

[tapple]

I did some more testing. It looks like there's a lot more than pid 17320 where there's a mismatch:

>>> import psutil
>>> import psutil._psutil_windows
>>> pidinfo = []
>>> for i in range(30000):
...     exists = psutil.pid_exists(i)
...     try:
...         proc = psutil.Process(i)
...     except Exception as e:
...         proc = e
...     try:
...         times = psutil._psutil_windows.proc_times(i)
...     except Exception as e:
...         times = e
...     pidinfo.append((exists, proc, times))
>>> mismatches = [exists != isinstance(proc, psutil.Process) for exists, proc, times in pidinfo]
>>> mismatched_pids=[i for i, mismatched in enumerate(mismatches) if mismatched]
>>> mismatched_info=[(i, ) + pidinfo[i] for i in mismatched_pids]
>>> running_pids = [i for i, (exists, proc, times) in enumerate(pidinfo) if exists]
>>> len(running_pids)
2801
>>> len(mismatched_info)
1923


>>> running_pids[:10]
[0, 4, 5, 6, 7, 68, 69, 70, 71, 108]
>>> mismatched_info[:10]
[
    (5, True, psutil.NoSuchProcess(pid=5, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (6, True, psutil.NoSuchProcess(pid=6, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (7, True, psutil.NoSuchProcess(pid=7, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (68, True, psutil.NoSuchProcess(pid=68, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (69, True, psutil.NoSuchProcess(pid=69, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (70, True, psutil.NoSuchProcess(pid=70, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (71, True, psutil.NoSuchProcess(pid=71, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (109, True, psutil.NoSuchProcess(pid=109, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (110, True, psutil.NoSuchProcess(pid=110, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (111, True, psutil.NoSuchProcess(pid=111, msg="process PID not found"), PermissionError(13, "Access is denied")),
]


>>> running_pids[-10:]
[28498, 28499, 28520, 28521, 28522, 28523, 28592, 28593, 28594, 28595]
>>> mismatched_info[-10:]
[
    (28494, True, psutil.NoSuchProcess(pid=28494, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28495, True, psutil.NoSuchProcess(pid=28495, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28496, True, psutil.NoSuchProcess(pid=28496, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28497, True, psutil.NoSuchProcess(pid=28497, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28498, True, psutil.NoSuchProcess(pid=28498, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28499, True, psutil.NoSuchProcess(pid=28499, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28592, True, psutil.NoSuchProcess(pid=28592, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28593, True, psutil.NoSuchProcess(pid=28593, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28594, True, psutil.NoSuchProcess(pid=28594, msg="process PID not found"), PermissionError(13, "Access is denied")),
    (28595, True, psutil.NoSuchProcess(pid=28595, msg="process PID not found"), PermissionError(13, "Access is denied")),
]

>>> pidinfo[17320]
(True, psutil.NoSuchProcess(pid=17320, msg="process PID not found"), PermissionError(13, "Access is denied"))

I checked the first 10 and last 10 mismatched pid's in task manager (I made sure to run it as Administrator). None were actually running. It seems that psutil.Process() is right when it doesn't match psutil.pid_exists()

I know that 17320 is a process that used to be running, but no longer is. I wonder if that's true of the rest of these. I'm pretty sure 17320 was a python process in vscode debugger that I force-killed by stopping the debugger

[tapple]

Since this is a permission denied error, I thought I'd see what happens if I actually used multiple users (I ran these tests on windows 10, not 11)

on tapple account (administrator):

(psutil-venv) C:\Users\tapple>python
Python 3.11.0 (main, Oct 24 2022, 18:13:38) [MSC v.1933 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import psutil
>>> p = psutil.Process()
>>> p
psutil.Process(pid=3592, name='python.exe', status='running', started='08:27:57')

on testuser account (not administrator):

(psutil-venv) C:\Users\testuser>python
Python 3.12.1 (tags/v3.12.1:2305ca5, Dec  7 2023, 22:03:25) [MSC v.1937 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import psutil
>>> p = psutil.Process()
>>> p
psutil.Process(pid=13180, name='python3.12.exe', status='running', started='08:30:05')
>>> psutil.pid_exists(3592)
True
>>> other = psutil.Process(3592)
>>> other
psutil.Process(pid=3592, name='python.exe', status='running', started='08:27:57')
>>> other.username()
Traceback (most recent call last):
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 730, in wrapper
    return fun(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 983, in username
    domain, user = cext.proc_username(self.pid)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [WinError 5] Access is denied: '(originated from OpenProcess)'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\__init__.py", line 744, in username
    return self._proc.username()
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 732, in wrapper
    raise convert_oserror(err, pid=self.pid, name=self._name)
psutil.AccessDenied: (pid=3592, name='python.exe')
>>> other.kill()
Traceback (most recent call last):
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 730, in wrapper
    return fun(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 917, in kill
    return cext.proc_kill(self.pid)
           ^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [WinError 5] Access is denied: '(originated from OpenProcess)'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\__init__.py", line 1304, in kill
    self._proc.kill()
  File "C:\Users\testuser\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 732, in wrapper
    raise convert_oserror(err, pid=self.pid, name=self._name)
psutil.AccessDenied: (pid=3592, name='python.exe')

back on tapple account (administrator):

>>> psutil.pid_exists(13180)
True
>>> other = psutil.Process(13180)
>>> other
psutil.Process(pid=13180, name='python3.12.exe', status='running', started='08:30:05')
>>> other.username()
Traceback (most recent call last):
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 730, in wrapper
    return fun(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 983, in username
    domain, user = cext.proc_username(self.pid)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [WinError 5] Access is denied: '(originated from OpenProcess)'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\__init__.py", line 744, in username
    return self._proc.username()
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 732, in wrapper
    raise convert_oserror(err, pid=self.pid, name=self._name)
psutil.AccessDenied: (pid=13180, name='python3.12.exe')
>>> other.kill()
Traceback (most recent call last):
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 730, in wrapper
    return fun(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 917, in kill
    return cext.proc_kill(self.pid)
           ^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [WinError 5] Access is denied: '(originated from OpenProcess)'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\__init__.py", line 1304, in kill
    self._proc.kill()
  File "C:\Users\tapple\psutil-venv\Lib\site-packages\psutil\_pswindows.py", line 732, in wrapper
    raise convert_oserror(err, pid=self.pid, name=self._name)
psutil.AccessDenied: (pid=13180, name='python3.12.exe')

So, psutil is able to get basic info about a process of another user without permission denied (including time), but not more detailed info.

In conclusion I think the correct behavior is: If there is permission denied getting basic process info, the process really does not exist. So:

• psutil.Process() is correct
• psutil.pid_exists() is buggy

[tapple]

There's a similar bug for linux, #1910. In that bug, it's the opposite: pid_exists() is correct and Process() is incorrect. So, the only sure-fire way to check that a process exists, in spite of these two bugs is:

proc = None
try:
    # check both pid_exists and Process. There are at least
    # 2 issues about them disagreeing in different directions.
    # See issues #1910 and #2359
    if psutil.pid_exists(pid):
        proc = psutil.Process(pid)
except (ProcessLookupError, psutil.NoSuchProcess):
    pass

if proc is not None:
    ...