Sunday, May 15, 2016

psutil 4.2.0, Windows services and Python

New psutil 4.2.0 is out. The main feature of this release is the support for Windows services:

>>> import psutil
>>> list(psutil.win_service_iter())
[<WindowsService(name='AeLookupSvc', display_name='Application Experience') at 38850096>,
 <WindowsService(name='ALG', display_name='Application Layer Gateway Service') at 38850128>,
 <WindowsService(name='APNMCP', display_name='Ask Update Service') at 38850160>,
 <WindowsService(name='AppIDSvc', display_name='Application Identity') at 38850192>,
>>> s = psutil.win_service_get('alg')
>>> s.as_dict()
{'binpath': 'C:\\Windows\\System32\\alg.exe',
 'description': 'Provides support for 3rd party protocol plug-ins for Internet Connection Sharing',
 'display_name': 'Application Layer Gateway Service',
 'name': 'alg',
 'pid': None,
 'start_type': 'manual',
 'status': 'stopped',
 'username': 'NT AUTHORITY\\LocalService'}

I did this mainly because I find pywin32 APIs too low level. Having something like this in psutil can be useful to discover and monitor services more easily. The code changes are here and here's the doc. The API for querying a service is similar to psutil.Process. You can get a reference to a service object by using its name (which is unique for every service) and then use name(), status(), etc..:

>>> s = psutil.win_service_get('alg')
>>> s.status()

Initially I thought to expose and provide a complete set of APIs to handle all aspects of service handling including start(), stop(), restart(), install(), uninstall() and modify() but I soon realized that I would have ended up reimplementing what pywin32 already provides at the cost of overcrowding psutil API (see my reasoning here). I think psutil should really be about monitoring, not about installing and modifying system stuff, especially something as critical as a Windows service.

Considerations about Windows services

For those of you who are not familiar with Windows, a service is something, generally an executable (.exe), which runs at system startup and keeps running in background. We can say they are the equivalent of a UNIX init script. All service are controlled by a "manager" which keeps track of their status and metadata (e.g. description, startup type) and with that you can start and stop them. It is interesting to note that since (most) services are bound to an executable (and hence a process) you can reference the process via its PID:

>>> s = psutil.win_service_get('sshd')
>>> s
<WindowsService(name='sshd', display_name='Open SSH server') at 38853046>
>>> p = psutil.Process(1865)
>>> p
<psutil.Process(pid=19547, name='sshd.exe') at 140461487781328>
>>> p.exe()

Other improvements

psutil 4.2.0 comes with 2 other enhancements for Linux:
  • psutil.virtual_memory() returns a new "shared" memory field. This is the same value reported by "free" cmdline utility.
  • I changed the way how /proc was parsed. Instead of reading /proc/{pid}/status line by line I used a regular expression. Here's the speedups:
    * Process.ppid() is 20% faster
    * Process.status() is 28% faster
    * is 25% faster
    * Process.num_threads() is 20% faster (on Python 3 only; on Python 2 it's a bit slower - I
       suppose re module received some improvements)