Truncated process name() should not raise ZombieProcess error

[giampaolo]

A recent failure observed on OpenBSD led me to an interesting consideration.

======================================================================
ERROR: psutil.tests.test_process.TestProcess.test_long_name
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/vagrant/psutil/psutil/_psbsd.py", line 566, in wrapper
    return fun(self, *args, **kwargs)
  File "/vagrant/psutil/psutil/_psbsd.py", line 684, in cmdline
    return cext.proc_cmdline(self.pid)
ProcessLookupError: [Errno 3] No such process

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/vagrant/psutil/psutil/tests/test_process.py", line 751, in test_long_name
    self.assertEqual(p.name(), os.path.basename(testfn))
  File "/vagrant/psutil/psutil/__init__.py", line 628, in name
    cmdline = self.cmdline()
  File "/vagrant/psutil/psutil/__init__.py", line 681, in cmdline
    return self._proc.cmdline()
  File "/vagrant/psutil/psutil/_psbsd.py", line 569, in wrapper
    raise ZombieProcess(self.pid, self._name, self._ppid)
psutil.ZombieProcess: PID still exists but it's a zombie (pid=48379)

----------------------------------------------------------------------

The exception above occurs sporadically. It originates from sysctl(KERN_PROC_ARGV):

psutil/psutil/arch/openbsd/proc.c

Line 149 in 0a81fa0

int argv_mib[] = {CTL_KERN, KERN_PROC_ARGS, pid, KERN_PROC_ARGV};

The error per se does not represent a bug in the OpenBSD cmdline() implemention because the process really is a zombie at that point (I'm not sure why it's a zombie - this seems only to occur only on OpenBSD for this specific test case - but that's not the point).

The interesting thing is that the test calls process name() (which succeeds, despite it's a zombie process), but since the process name is too long it gets truncated to 15 chars (this is a UNIX thing) so psutil tries to guess the remaining characters from the process cmdline(), which fails:

psutil/psutil/__init__.py

Lines 623 to 630 in 0a81fa0

	# On UNIX the name gets truncated to the first 15 characters.
	# If it matches the first part of the cmdline we return that
	# one instead because it's usually more explicative.
	# Examples are "gnome-keyring-d" vs. "gnome-keyring-daemon".
	try:
	cmdline = self.cmdline()
	except AccessDenied:
	pass

The problem to fix here is that, if name() succeeds but cmdline() fails, we should not raise ZombieProcess: we should simply return the (truncated) process name(), because that is better than nothing. Not on OpenBSD but on all platforms.