psutil.process_iter() raise TypeError (it's not thread safe)

[giampaolo]

To reproduce:

import psutil, threading, traceback

def worker():
    try:
        for p in psutil.process_iter():
            with p.oneshot():
                p.cpu_times()
    except Exception as err:
        with lock:
            traceback.print_exc()

lock = threading.Lock()
for x in range(1000):
    t = threading.Thread(target=worker)
    t.start()

...prints:

Traceback (most recent call last):
  File "foo.py", line 56, in worker
    for p in psutil.process_iter():
  File "/home/giampaolo/svn/psutil/psutil/__init__.py", line 1434, in process_iter
    ls = sorted(list(_pmap.items()) +
TypeError: '<' not supported between instances of 'NoneType' and 'Process'
Traceback (most recent call last):
  File "foo.py", line 56, in worker
    for p in psutil.process_iter():
  File "/home/giampaolo/svn/psutil/psutil/__init__.py", line 1434, in process_iter
    ls = sorted(list(_pmap.items()) +
TypeError: '<' not supported between instances of 'NoneType' and 'Process'
Traceback (most recent call last):
  File "foo.py", line 56, in worker
    for p in psutil.process_iter():
  File "/home/giampaolo/svn/psutil/psutil/__init__.py", line 1434, in process_iter
    ls = sorted(list(_pmap.items()) +
...