os.kill on windows

[tebeka]

BPO	1220212
Nosy	@tim-one, @loewis, @tebeka, @tiran, @tpn, @DinoV, @voidspace, @briancurtin
Files	diff.zip: Zip of source and documentation kill.diff issue1220212.patch faq_update.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/briancurtin'
closed_at = <Date 2010-04-12.18:11:07.992>
created_at = <Date 2005-06-14.09:11:53.000>
labels = ['interpreter-core', 'type-feature']
title = 'os.kill on windows'
updated_at = <Date 2010-04-12.18:11:07.991>
user = 'https://github.com/tebeka'

bugs.python.org fields:

activity = <Date 2010-04-12.18:11:07.991>
actor = 'brian.curtin'
assignee = 'brian.curtin'
closed = True
closed_date = <Date 2010-04-12.18:11:07.992>
closer = 'brian.curtin'
components = ['Interpreter Core']
creation = <Date 2005-06-14.09:11:53.000>
creator = 'tebeka'
dependencies = []
files = ['6690', '6691', '16739', '16765']
hgrepos = []
issue_num = 1220212
keywords = ['patch']
message_count = 30.0
messages = ['48455', '48456', '48457', '48458', '48459', '48460', '48461', '48462', '48463', '48464', '59787', '59800', '62468', '101774', '101775', '101777', '101828', '101846', '101847', '101851', '101970', '101973', '102184', '102200', '102202', '102213', '102375', '102379', '102385', '102965']
nosy_count = 13.0
nosy_names = ['tim.peters', 'loewis', 'nnorwitz', 'tebeka', 'andersjm', 'techtonik', 'christian.heimes', 'kap4020', 'Technologov', 'trent', 'dino.viehland', 'michael.foord', 'brian.curtin']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue1220212'
versions = ['Python 2.7', 'Python 3.2']

[tebeka]

This patch enables os.kill on windows. This way there
will be an "out of the box" way to kill process on windows.

Basically kill calls TerminateProcess and the "signal"
paramer will be the process return code.

Don't have CVS access today so I'm sending the whole
files in a zip (sorry).

Also some config wizard need to change the winsows
configuration and set HAVE_KILL.

[loewis]

Logged In: YES
user_id=21627

Converted to unified diff.

[kap4020]

Logged In: YES
user_id=1537118

So is there a reason this isn't in the latest Python? The
patch is tiny.

[nnorwitz]

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user_id=33168

Karl, can you test this patch and verify it works? It would
be especially helpful to test on Win9x and WinNT variants.
Are there tests included? Is there a doc patch? These are
some of the potential reasons this isn't included. As for
me, I can't test this patch (no windows), so it's a
non-starter. If you'd like to help out, we could use the help.

[loewis]

Logged In: YES
user_id=21627

As is, the patch has two major problems:

• TerminateProcess expects a process handle, not a process
  ID. This makes the patch pretty useless: To kill a process
  other than yourself, you need to call OpenProcess first (or
  obtain a process handle in some other way, e.g. by having
  created it).

• if the call fails, it uses posix_error to report the
  problem. However, posix_error expects that errno is set,
  which isn't the case here.

Furthermore, this patch would duplicate
_subprocess.TerminateProcess, which already exposes
TerminateProcess (plus allowing to specify the exit code).

So in its current form, I think the patch should be rejected.

[tebeka]

Logged In: YES
user_id=358087

IIRC (the patch was done a long time ago), Python uses the
process handle as the process id, I've tested the code and
it worked.

I agree that the patch need more work, mainly the error
return value.

At least on Python 2.4.3, TerminateProcess is not exposed by
_subprocss (or subprocess).

I still think that having a way to kill a process OOTB on
win32 is very important, pretty swamped right now but I'll
try to improve the patch.

[loewis]

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user_id=21627

"Python uses the process handle as process id" makes no real
sense - Win32 works differently. You can't terminate a
process without a handle, and you can't just "use" the
process id as the handle. Perhaps some use cases for the API
would need to be defined first.

[tim-one]

Logged In: YES
user_id=31435

Martin, FYI, on Windows the os.spawn() functions return the
process handle, so that's the natural use case: killing a
process spawned by Python's os.spawn*(). This is a little
confusing because the spawn() functions are documented as
returning "the process ID", and verbiage inside the spawn
docs explains that it doesn't really mean "process ID" on
Windows.

[loewis]

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user_id=21627

Ah, ok. Given that _subprocess already offers that
functionality, I'm still -1 on adding it to "nt". Adding
some kind of OpenProcess might be more useful, but then,
people can get to all these functions through ctypes, as well.

[tim-one]

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Well, os.waitpid() on Windows also takes a process handle.
This was (of course) deliberate, so that os.waitpid() could
use the thingie returned by os.spawn() on Windows. If
os.kill() were ever added to Windows, I think it would be
quite natural for it to take a process handle too, and for
the same reason (Python code mixing os.{spawn,waitpid,kill}
could be the same across platforms). Zope's ZODB relies on
mixing spawn and waitpid this way, and Zope's ZRS implements
its own kill function on Windows so that the rest of the
Python code can just do kill(id) on all platforms (where
id is always something obtained from os.spawn()).

[tiran]

This should be implemented differently. Users should substitute their
popen and exec calls with subprocess. The subprocess.Popen class should
gain two new methods terminate() and send_signal(int) where send_signal
is restricted to SIGKILL (+SIGTERM ?) on Windows. The idea was discussed
on the Python dev list early last year.

[tebeka]

Users should substitute their popen and exec calls with subprocess
As long as popen and exec are available, users are free to use them (and
probably will :)

The Popen(...).terminate() works only if I'm the one who started the
process. However there are cases where I want to kill all running python
processes. The pids to be killed will come from somewhere else (ps,
plist, ...).

[Technologov]

Yes, this feature would be very important for me too...

Anybody knows, _when_ it will be integrated into Python ?

If this bugzilla supports email notifications, Please add me as "CC" for
this bug.

-Technologov

[voidspace]

It would be really useful to be able to send signal.SIGINT to processes on Windows using os.kill(...). The patch as described sounds like it would have a different signature to the standard implementation of os.kill(...) which takes a pid and a signal type.

IronPython 2.7 will have an os.kill implementation. Looks like it only supports signal.SIGINT and signal.SIGBREAK and just calls:

Process toKill = Process.GetProcessById(pid);
toKill.Kill()

[voidspace]

I'm wrong. First IronPython tries:

NativeSignal.GenerateConsoleCtrlEvent(PythonSignal.CTRL_C_EVENT, ...)

But with the comment:

//The following calls to GenerateConsoleCtrlEvent will fail under
//most circumstances. We'll try them any ways though as this seems
//to be the only mechanism in Windows to send signals to processes

It falls back to just killing the process.

[voidspace]

Aaaand the IronPython implementation of NativeSignal.GenerateConsoleCtrlEvent(PythonSignal.CTRL_C_EVENT, ...)
delegates to Kernel32.GenerateConsoleCtrlEvent.

[voidspace]

To make it clear, even though it would be incomplete, a partial implementation of os.kill(...) for Windows would be very useful and provide some level of compatibility with applications that use os.kill (so even if os.kill(...) duplicates functionality in other modules - although that was disputed - it should be provided for compatibility reasons).

An implementation similar to the IronPython one is probably the best that can be managed and would still be useful: accepting only signal.SIGINT and signal.SIGBREAK and first trying Kernel32.GenerateConsoleCtrlEvent, falling back to killing the process.

[loewis]

So, Michael, what do you think: should os.kill expect a process handle, or a process ID?

[voidspace]

Hmm... well my particular use case is that it should work with the value returned by os.getpid(). If that is a process handle then it is nice and convenient to just use process handles. The docs don't specify so I bet it returns a pid. :-(

However Brian Curtin might want to weigh in on this as he has been looking at implementing this and there might be constraints.

[briancurtin]

I have this working with process IDs and my vote would be to keep it that way, as it would stay in-line with the other platforms, and it seems to work so far. I would imagine that was also IronPython's goal.

I'm still working on the test portion of the patch. It should be ready shortly.

[briancurtin]

Here is a patch with some tests and doc changes.

I'm having trouble coming up with tests which will work with CTRL_C_EVENT and CTRL_BREAK_EVENT. Based on my understanding of GenerateConsoleCtrlEvent, I figured this example (http://msdn.microsoft.com/en-us/library/ms685049%28v=VS.85%29.aspx) would be receptive to CTRL+C when started as a subprocess, but it doesn't work. I also figured "python -c "input()"" started as a subprocess could be killed with CTRL_C_EVENT, but it doesn't work either.

[briancurtin]

Removed an unnecessary goto and fixed a few tab/space inconsistencies (ugh).

[voidspace]

After discussion with Brian it seems like it should be possible for os.kill(...) on Windows to support both pids *and* process handles. This seems ideal.

[briancurtin]

Michael, do you have an example of something which returns a handle? This current patch doesn't work with handles, but it wouldn't be hard to add it. I could make it work with the _handle object of a Popen object, but you could just as easily call os.kill on the pid of the Popen object. I don't know of any Python-wide handle object...I know subprocess has it's own, and don't really know what other functions are returning handles.

Anyways, this patch includes an additional test script which uses ctypes to setup a console control handler, and CTRL_BREAK_EVENT is tested successfully. However, CTRL_C_EVENT is not. See http://msdn.microsoft.com/en-us/library/ms686016%28v=VS.85%29.aspx for details, but I'm not able to get the subprocess to work with CTRL+C. Calling SetConsoleCtrlHandler(NULL, FALSE) either in the script, test_os, or in _subprocess.c does not change anything, although it seems that it should. The CTRL_C_EVENT test is currently skipped in the patch until I can figure that out.

[voidspace]

According to earlier discussion in this issue os.spawn() return process handles on Windows.

[briancurtin]

Committed to trunk in r79633 after talking with Michael about it. I'll forward port it after the 2.7 beta goes out.

[techtonik]

FAQ should be updated http://www.python.org/doc/faq/windows/#how-do-i-emulate-os-kill-in-windows

[briancurtin]

How about something like this patch?

[techtonik]

Seems good to me, even though I'd rewrite some parts like this:

• Prior to Python 2.7 and 3.2, to terminate a process, you can use ctypes::
  + Prior to Python 2.7 and 3.2, you can use linksomehow:`ctypes` to
  terminate a process::

...

In newer Python versions :func:`os.kill` works on Windows with the
additional feature of being able to send CTRL+C and CTRL+BREAK to
console subprocesses that understand these signals.

...

anatoly t.

On Mon, Apr 5, 2010 at 6:38 PM, Brian Curtin <report@bugs.python.org> wrote:

Brian Curtin <curtin@acm.org> added the comment:

How about something like this patch?

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Added file: http://bugs.python.org/file16765/faq_update.diff

---

Python tracker <report@bugs.python.org>
<http://bugs.python.org/issue1220212\>

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[briancurtin]

Ported to py3k in r80008.

FAQ text updated in r80009 and r80010.