Blog posts for tags/python

  1. psutil 5.3.0 and full unicode support

    psutil 5.3.0 is finally out. This release is a major one, as it includes tons of improvements and bugfixes, probably like no other previous release. It is interesting to notice how huge the diff between 5.2.2 and 5.3.0 is. This is due to the fact that I've been travelling quite a lot this year, so I kept postponing it. It may sound weird but I consider publishing a new release and write a blog post about more stressful than working on the release itself. =). Anyway, here goes.

    Full Unicode support

    This is the biggest change. In order to achieve this I had to refactor all functions and internals either returning or accepting a string. Incidentally this helped me having a better understanding of how Unicode works and how it should be handled at the C level in terms of differences between Python 2 and 3. Issue #1040 includes all the reasonings I've been through and potentially serves as a documentation for people who are facing a similar task (handling Unicode in C for both Python 2 and 3). Up until version 5.2.x psutil functions returning a string had different problems as they could:

    • raise decoding error on Python 3 in case of non-ASCII string
    • return unicode instead of str (Python 2)
    • return incorrect / invalid encoded data in case of non-ASCII string

    5.3.0 fixes these three issues and consolidates the correct handling of Unicode strings. On Windows this was achieved by using Unicode-specific Windows APIs. The notes below describe how Unicode and strings in general are handled internally by psutil and they apply to any API returning a string such as Process.exe or Process.cwd, including non-filesystem related methods such as Process.username or WindowsService.description:

    • all strings are encoded by using the OS filesystem encoding (sys.getfilesystemencoding()) which varies depending on the platform (e.g. "UTF-8" on OSX, "mbcs" on Win)
    • no API call is supposed to crash with UnicodeDecodeError
    • instead, in case of badly encoded data returned by the OS, the following error handlers are used to replace the corrupted characters in the string:
    • on Python 2 all APIs return bytes (str type), never unicode
    • on Python 2 you can go back to unicode by doing:
    >>> unicode(proc.exe(), sys.getdefaultencoding(), errors="replace")
    

    Improved process_iter() function

    process_iter() accepts two new parameters in order to invoke Process.as_dict() internally: "attrs" and "ad_value". With this you can iterate over all processes in one shot without having to catch NoSuchProcess explicitly. Before:

    >>> import psutil
    >>> for proc in psutil.process_iter():
    ...     try:
    ...         pinfo = proc.as_dict(attrs=['pid', 'name'])
    ...     except psutil.NoSuchProcess:
    ...         pass
    ...     else:
    ...         print(pinfo)
    ...
    {'pid': 1, 'name': 'systemd'}
    {'pid': 2, 'name': 'kthreadd'}
    {'pid': 3, 'name': 'ksoftirqd/0'}
    ...
    

    Now:

    >>> import psutil
    >>> for proc in psutil.process_iter(attrs=['pid', 'name']):
    ...     print(proc.info)
    ...
    {'pid': 1, 'name': 'systemd'}
    {'pid': 2, 'name': 'kthreadd'}
    {'pid': 3, 'name': 'ksoftirqd/0'}
    

    This improves expressiveness as it makes it possible to use nice list/dict comprehensions. Here's some examples.

    Processes having "python" in their name:

    >>> from pprint import pprint as pp
    >>> pp([p.info for p in psutil.process_iter(attrs=['pid', 'name']) if 'python' in p.info['name']])
    [{'name': 'python3', 'pid': 21947},
    {'name': 'python', 'pid': 23835}]
    

    Processes owned by user:

    >>> import getpass
    >>> pp([(p.pid, p.info['name']) for p in psutil.process_iter(attrs=['name', 'username']) if p.info['username'] == getpass.getuser()])
    (16832, 'bash'),
    (19772, 'ssh'),
    (20492, 'python')]
    

    Processes actively running:

    >>> pp([(p.pid, p.info) for p in psutil.process_iter(attrs=['name', 'status']) if p.info['status'] == psutil.STATUS_RUNNING])
    [(1150, {'name': 'Xorg', 'status': 'running'}),
    (1776, {'name': 'unity-panel-service', 'status': 'running'}),
    (20492, {'name': 'python', 'status': 'running'})]
    

    Automatic overflow handling of numbers

    On very busy or long-lived system systems numbers returned by disk_io_counters() and net_io_counters() functions may wrap (restart from zero). Up to version 5.2.x you had to take this into account while now this is automatically handled by psutil (see: #802). If a "counter" restarts from 0 psutil will add the value from the previous call for you so that numbers will never decrease. This is crucial for applications monitoring disk or network I/O in real time. Old behavior can be resumed by passing nowrap=True argument.

    SunOS Process environ()

    Process.environ() is now available also on SunOS (see #1091).

    Other improvements and bug fixes

    Amongst others, here's a couple of important bug fixes I'd like to mention:

    • #1044: on OSX different Process methods could incorrectly raise AccessDenied for zombie processes. This was due to poor proc_pidpath OSX API.
    • #1094: on Windows, pid_exists() may lie due to the poor OpenProcess Windows API which can return a handle even when a process PID no longer exists. This had repercussions for many Process methods such as cmdline(), environ(), cwd(), connections() and others which could have unpredictable behaviors such as returning empty data or erroneously raise NoSuchProcess exceptions. For the same reason (broken OpenProcess API), processes could unexpectedly stick around after using terminate() and wait().

    BSD systems also received some love (NetBSD and OpenBSD in particular). Different memory leaks were fixed and functions returning connected sockets were partially rewritten. The full list of enhancement and bug fixes can be seen here.

    About me

    I would like to spend a couple more words about my current situation. Last year (2016) I relocated to Prague and remote worked from there the whole year (it's been cool - great city!). This year I have mainly been resting in Turin (Italy) due to some health issues and travelling across Asia once I started to recover. I am currently in Shenzhen, China, and unless the current situation with North Korea gets worse I'm planning to continue my trip until November and visit Taiwan, South Korea and Japan. Once I'm finished the plan is to briefly return to Turin (Italy) and finally return to Prague. By then I will probably be looking for a new (remote) gig again, so if you have anything for me by November feel free to send me a message. ;-)

  2. psutil 5.1.1 system temperature, battery and CPU frequency

    OK, here's another psutil release. Main highlights of this release are sensors-related APIs.

    Temperatures

    It is now possible to retrieve hardware temperatures. The relevant commit is here. Unfortunately this is Linux only. I couldn't manage to implement this on other platforms mainly for two reasons:

    • On Windows it is hard to do this in a hardware agnostic fashion. I bumped into 3 different approaches, all using WMI, and none of them worked with my hardware so I gave up.
    • On OSX it appears it is possible to retrieve temperatures relatively easy, but I have a virtualized OSX box which does not support sensors, so basically I gave up on this due to lack of hardware. If somebody wants to give it a try be my guest.
    >>> import psutil
    >>> psutil.sensors_temperatures()
    {'acpitz': [shwtemp(label='', current=47.0, high=103.0, critical=103.0)],
     'asus': [shwtemp(label='', current=47.0, high=None, critical=None)],
     'coretemp': [shwtemp(label='Physical id 0', current=52.0, high=100.0, critical=100.0),
                  shwtemp(label='Core 0', current=45.0, high=100.0, critical=100.0),
                  shwtemp(label='Core 1', current=52.0, high=100.0, critical=100.0),
                  shwtemp(label='Core 2', current=45.0, high=100.0, critical=100.0),
                  shwtemp(label='Core 3', current=47.0, high=100.0, critical=100.0)]}
    

    Battery status

    This works on Linux, Windows and FreeBSD and provides battery status information. The relevant commit is here.

    >>> import psutil
    >>>
    >>> def secs2hours(secs):
    ...     mm, ss = divmod(secs, 60)
    ...     hh, mm = divmod(mm, 60)
    ...     return "%d:%02d:%02d" % (hh, mm, ss)
    ...
    >>> battery = psutil.sensors_battery()
    >>> battery
    sbattery(percent=93, secsleft=16628, power_plugged=False)
    >>> print("charge = %s%%, time left = %s" % (batt.percent, secs2hours(batt.secsleft)))
    charge = 93%, time left = 4:37:08
    

    CPU frequency

    Available under Linux, Windows and OSX. Relevant commit is here. Linux is the only platform which reports the real-time value (always changing), on all other platforms current frequency is represented as the nominal “fixed” value.

    >>> import psutil
    >>> psutil.cpu_freq()
    scpufreq(current=931.42925, min=800.0, max=3500.0)
    >>> psutil.cpu_freq(percpu=True)
    [scpufreq(current=2394.945, min=800.0, max=3500.0),
     scpufreq(current=2236.812, min=800.0, max=3500.0),
     scpufreq(current=1703.609, min=800.0, max=3500.0),
     scpufreq(current=1754.289, min=800.0, max=3500.0)]
    

    What CPU a process is on

    This will let you know what CPU number a process is currently running on, which is somewhat related to the existent cpu_affinity() functionality. The relevant commit is here. It is interesting to use this method to visualize how the OS scheduler continuously evenly reassigns processes to different CPUs (see cpu_distribution.py script).

    CPU affinity

    A new syntax can now be used as an alias for "set affinity against all eligible CPUs".

    Process().cpu_affinity([])
    

    This was implemented because it turns out on Linux it is not always possible to set affinity against all CPUs. Having such an alias is also a shortcut to avoid doing this, which is kinda verbose:

    psutil.Process().cpu_affinity(list(range(psutil.cpu_count())))
    

    Other bug fixes

    See full list.

  3. psutil 5.5.0 is twice as fast

    OK, this is a big one. Starting from psutil 5.0.0 you can query multiple Process information around twice as fast than with previous versions (see original ticket and updated doc). It took me 7 months, 108 commits and a massive refactoring of psutil internals (here is the big commit), and I can safely say this is one of the best improvements and long standing issues which have been addressed in a major psutil release. Here goes.

    The problem

    Except for some cases, the way different process information are retrieved varies depending on the OS. Sometimes it requires reading a file in /proc filesystem (Linux), some other times it requires using C (Windows, BSD, OSX, SunOS), but every time it's done differently. Psutil abstracts this complexity by providing a nice high-level interface so that you, say, call Process.name() without worrying about what happens behind the curtains or on what OS you're on.

    Internally, it is not rare that multiple process info (e.g. name(), ppid(), uids(), create_time()) may be fetched by using the same routine. For example, on Linux we read /proc/stat to get the process name, terminal, CPU times, creation time, status and parent PID, but only one value is returned and the others are discarded. On Linux the code below reads /proc/stat 6 times:

    >>> import psutil
    >>> p = psutil.Process()
    >>> p.name()
    >>> p.cpu_times()
    >>> p.create_time()
    >>> p.ppid()
    >>> p.status()
    >>> p.terminal()
    

    Another example is BSD. In order to get process name, memory, CPU times and other metrics, a single sysctl() call is necessary, but again, because of how psutil used to work so far that same sysctl() call is executed every time (see here, here, and so on), one information is returned (say name()) and the rest is discarded. Not anymore.

    Do it in one shot

    It appears clear how the approach described above is not efficient, also considering that applications similar to top, htop, ps or glances usually collect more than one info per-process. psutil 5.0.0 introduces a new oneshot() context manager. When used, the internal routine is executed once (in the example below on name()) and the other values are cached. The subsequent calls sharing the same internal routine (read /proc/stat, call sysctl() or whatever) will return the cached value. With psutil 5.0.0 the code above can be rewritten like this, and on Linux it will run 2.4 times faster:

    >>> import psutil
    >>> p = psutil.Process()
    >>> with p.oneshot():
    ...     p.name()
    ...     p.cpu_times()
    ...     p.create_time()
    ...     p.ppid()
    ...     p.status()
    ...     p.terminal()
    

    Implementation

    One great thing about psutil design is its abstraction. It is dived in 3 "layers". The first layer is represented by the main Process class (python), which is what dictates the end-user high-level API. The second layer is the OS-specific Python module which is thin wrapper on top of the OS-specific C extension module (third layer). Because this was organized this way (modularly) the refactoring was reasonably smooth. In order to do this I first refactored those C functions collecting multiple info and grouped them in a single function (e.g. see BSD implementation). Then I wrote a decorator which enables the cache only when requested (when entering the context manager) and decorated the "grouped functions" with with it. The whole thing is enabled on request by the highest-level oneshot() context manager, which is the only thing which is exposed to the end user. Here's the decorator:

    def memoize_when_activated(fun):
        """A memoize decorator which is disabled by default. It can be
        activated and deactivated on request.
        """
        @functools.wraps(fun)
        def wrapper(self):
            if not wrapper.cache_activated:
                return fun(self)
            else:
                try:
                    ret = cache[fun]
                except KeyError:
                    ret = cache[fun] = fun(self)
                return ret
    
        def cache_activate():
            """Activate cache."""
            wrapper.cache_activated = True
    
        def cache_deactivate():
            """Deactivate and clear cache."""
            wrapper.cache_activated = False
            cache.clear()
    
        cache = {}
        wrapper.cache_activated = False
        wrapper.cache_activate = cache_activate
        wrapper.cache_deactivate = cache_deactivate
        return wrapper
    

    In order to measure the various speedups I finally wrote a benchmark script (well, two actually) and kept tuning until I was sure the various changes made psutil actually faster. The benchmark scripts calculate the speedup you can get if you call all the "grouped" methods together (best case scenario).

    Linux: +2.56x speedup

    Linux process is the only pure-python implementation as (almost) all process info are gathered by reading files in the /proc filesystem. /proc files typically contain different information about the process and /proc/PID/stat and /proc/PID/status are the perfect examples. That's why on Linux we aggregate them in 3 groups. The relevant part of the Linux implementation can be seen here.

    Windows: from +1.9x to +6.5x speedup

    Windows is an interesting one. In normal circumstances, if we're querying a process owned by our user, we group together only process' num_threads(), num_ctx_switches() and num_handles(), getting a +1.9x speedup if we access those methods in one shot. Windows is particular though, because certain methods use a dual implementation: a "fast method" is attempted first, but if the process is owned by another user it fails with AccessDenied. In that case psutil falls back on using a second "slower" method (see here for example). The second method is slower because it iterates over all PIDs but differently than "plain" Windows APIs it can be used to get multiple info in one shot: num threads, context switches, handles, CPU times, create time and IO counters. That is why querying processes owned by other users results in an impressive +6.5 speedup.

    OSX: +1.92x speedup

    On OSX we can get 2 groups of information. With sysctl() syscall we get process parent PID, uids, gids, terminal, create time, name. With proc_info() syscall we get CPU times (for PIDs owned by another user) memory metrics and ctx switches. Not bad.

    BSD: +2.18x speedup

    BSD was an interesting one as we gather a tons of process info just by calling sysctl() (see implementation). In a single shot we get process name, ppid, status, uids, gids, IO counters, CPU and create times, terminal and ctx switches.

    SunOS: +1.37 speedup

    SunOS implementation is similar to Linux implementation in that it reads files in /proc filesystem but differently from Linux this is done in C. Also in this case, we can group different metrics together (see here and here).

  4. psutil 4.4.0: improved Linux memory metrics

    OK, here's another psutil release. Main highlights of this release are more accurate memory metrics on Linux and different OSX fixes. Here goes.

    Linux virtual memory

    This new release sets a milestone regarding virtual_memory() metrics on Linux which are now calculated way more precisely (see commit). Across the years different people complained that the numbers reported by virtual_memory() were not accurate or did not match the ones reported by free command line utility exactly (see #862, #685, #538). As such I investigated how "available memory" is calculated on Linux and indeed psutil were doing it wrong. It turns out "free" cmdline itself, and many other similar tools, also did it wrong up until 2 years ago when somebody finally decided to accurately calculate the available system memory straight into the Linux kernel and expose this info to user-level applications. Starting from Linux kernel 3.14, a new "MemAvailable" column was added to /proc/meminfo and this is how psutil now determines available memory. Because of this both "available" and "used" memory fields returned by virtual_memory() precisely match free command line utility. As for older kernels (< 3.14), psutil tries to determine this value by using the same algorithm which was used in the original Linux kernel commit. Free cmdline utility source code also inspired an additional fix which prevents available memory overflowing total memory on LCX containers.

    OSX fixes

    For many years the OSX development of psutil occurred on a very old OSX 10.5 version, which I emulated via VirtualBox. The OS itself was a hacked version of OSX, called iDeneb. After many years I finally managed to get access to a more recent version of OSX (El Captain) thanks to VirtualBox + Vagrant. With this I finally had the chance to address many long standing OSX bugs. Here's the list:

    • 514: fix Process.memory_maps() segfault (critical!).
    • 783: Process.status() may erroneously return "running" for zombie processes.
    • 908: different process methods could erroneously mask the real error for high-privileged PIDs and raise NoSuchProcess and AccessDenied instead of OSError and RuntimeError.
    • 909: Process.open_files() and Process.connections() methods may raise OSError with no exception set if process is gone.
    • 916: fix many compilation warnings.

    Improved procinfo.py script

    procinfo.py is a script which shows psutil capabilities regarding obtaining different info about processes. I improved it so that now it reports a lot more info. Here's a sample output:

    $ python scripts/procinfo.py
    pid           4600
    name          chrome
    parent        4554 (bash)
    exe           /opt/google/chrome/chrome
    cwd           /home/giampaolo
    cmdline       /opt/google/chrome/chrome
    started       2016-09-19 11:12
    cpu-tspent    27:27.68
    cpu-times     user=8914.32, system=3530.59,
                  children_user=1.46, children_system=1.31
    cpu-affinity  [0, 1, 2, 3, 4, 5, 6, 7]
    memory        rss=520.5M, vms=1.9G, shared=132.6M, text=95.0M, lib=0B,
                  data=816.5M, dirty=0B
    memory %      3.26
    user          giampaolo
    uids          real=1000, effective=1000, saved=1000
    uids          real=1000, effective=1000, saved=1000
    terminal      /dev/pts/2
    status        sleeping
    nice          0
    ionice        class=IOPriority.IOPRIO_CLASS_NONE, value=0
    num-threads   47
    num-fds       379
    I/O           read_count=96.6M, write_count=80.7M,
                  read_bytes=293.2M, write_bytes=24.5G
    ctx-switches  voluntary=30426463, involuntary=460108
    children      PID    NAME
                  4605   cat
                  4606   cat
                  4609   chrome
                  4669   chrome
    open-files    PATH
                  /opt/google/chrome/icudtl.dat
                  /opt/google/chrome/snapshot_blob.bin
                  /opt/google/chrome/natives_blob.bin
                  /opt/google/chrome/chrome_100_percent.pak
                  [...]
    connections   PROTO LOCAL ADDR            REMOTE ADDR               STATUS
                  UDP   10.0.0.3:3693         *:*                       NONE
                  TCP   10.0.0.3:55102        172.217.22.14:443         ESTABLISHED
                  UDP   10.0.0.3:35172        *:*                       NONE
                  TCP   10.0.0.3:32922        172.217.16.163:443        ESTABLISHED
                  UDP   :::5353               *:*                       NONE
                  UDP   10.0.0.3:59925        *:*                       NONE
    threads       TID              USER          SYSTEM
                  11795             0.7            1.35
                  11796            0.68            1.37
                  15887            0.74            0.03
                  19055            0.77            0.01
                  [...]
                  total=47
    res-limits    RLIMIT                     SOFT       HARD
                  virtualmem             infinity   infinity
                  coredumpsize                  0   infinity
                  cputime                infinity   infinity
                  datasize               infinity   infinity
                  filesize               infinity   infinity
                  locks                  infinity   infinity
                  memlock                   65536      65536
                  msgqueue                 819200     819200
                  nice                          0          0
                  openfiles                  8192      65536
                  maxprocesses              63304      63304
                  rss                    infinity   infinity
                  realtimeprio                  0          0
                  rtimesched             infinity   infinity
                  sigspending               63304      63304
                  stack                   8388608   infinity
    mem-maps      RSS      PATH
                  381.4M   [anon]
                  62.8M    /opt/google/chrome/chrome
                  15.8M    /home/giampaolo/.config/google-chrome/Default/History
                  6.6M     /home/giampaolo/.config/google-chrome/Default/Favicons
                  [...]
    

    NIC netmask on Windows

    net_if_addrs() on Windows is now able to return the netmask.

    Other improvements and bug fixes

    Just take a look at the HISTORY file.

  5. psutil 4.2.0: Windows services in 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.name()
    'alg'
    >>> s.status()
    'stopped'
    

    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>
    >>> s.pid()
    1865
    >>> p = psutil.Process(1865)
    >>> p
    <psutil.Process(pid=19547, name='sshd.exe') at 140461487781328>
    >>> p.exe()
    'C:\CygWin\bin\sshd'
    

    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
      • Process.name() 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)

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