[python-win32] Silent crashes in calls to a COM object in Python

Mark Hammond skippy.hammond at gmail.com
Wed Apr 25 02:11:17 CEST 2012

On 25/04/2012 7:14 AM, Deniz Pelvan wrote:
> Hello again Mark,I am not sure what you mean by direct call? The COM
> object is loaded inproc (i.e. the COM object is not in a service proc
> and I don't see any temp processes created by python or pywin32) but
> I thought you were using the IDispatch interface to find and load the
> dll & object rather than a direct interface call (which would require
> type library etc. knowledge).

IDispatch is just an interface like any other.  If you call an inproc 
interface, you are making a normal direct call across DLLs, almost as if 
you had linked to the DLL directly - just the mechanics of that 
"linking" change.

> As for the test app, it is not using
> the IDispatch interface so the IDispatch might be causing trouble.

This sounds very likely.

> The
> prompt I mentioned is the Python interpreter prompt, btw.

So it sounds like one of your IDispatch interfaces is prematurely 
returning S_OK - ie, nothing is crashing but your method is just 
returning before you expect it.


I will try
> to dig deeper into the python interpreter with the debugger and see
> if there is anything else I can catch. Thanks for the helpDeniz
> ----------------------------------------
>> Date: Tue, 24 Apr 2012 15:07:39 +1000 From:
>> mhammond at skippinet.com.au To: i_pelvan at hotmail.com CC:
>> python-win32 at python.org Subject: Re: [python-win32] Silent crashes
>> in calls to a COM object in Python
>> On 24/04/2012 2:55 PM, Deniz Pelvan wrote:
>>> Hello Mark, As I mentioned, I ran my COM interface with another
>>> Win32 test app under a MSVC debugger for hours without any
>>> problem. I attached a debugger to the Python process but with
>>> Python, the script goes all the way to that call, waits about a
>>> minute in that call and then without throwing any exceptions or
>>> errors, the script stops running (i.e. the next line in the
>>> script never gets called) and Python drops back to the prompt.
>>> Nothing gets caught by the debugger.
>> I'm not quite with you here - I assume Python is using an inproc
>> version of your object, so the COM call made by Python is actually
>> a direct call into your object. In that scenario, I can't see how
>> execution will return to Python without your object actually
>> returning.
>> If it is not an inproc object, then it may be that the default COM
>> marshaller is indeed timing out, but I'm not familiar with that or
>> under what circumstances this will happen but it might be worth
>> looking at what "apartment" things are running in, and/or any other
>> differences between the environment your test app runs under and
>> that of Python.
>> I'm also not sure what prompt you are referring to - the Python
>> prompt or a cmdline prompt? Either way, with the debugger you
>> should be able to see the call to IDispatch::Invoke made by Python
>> (hrm - but sadly you will probably need to build pywin32 yourself
>> so you get debugging symbols). If you can see that call to
>> Invoke(), you should be able to determine if that call never
>> returns (in which case it is almost certainly the marshaller) or if
>> it returns with an error code or 0.
>> There isn't much else in Python or pywin32 that can help -
>> depending on how you construct the COM object, there are one or 2
>> places where the Python code calls "dispatchobject.Invoke()" (or
>> dispatchobject.InvokeTypes()) which is basically a direct call from
>> the interpreter into win32com/src/PyIDispatch.cpp - the debugger is
>> the best tool for that...
>> Mark
>>> I was wondering if there are any options either in the Python
>>> interpreter or in pywin32 (or maybe a debug version) that can
>>> show what is happening internally, especially over the COM
>>> dispatch... Thanks in advance Deniz
>>>> Date: Tue, 24 Apr 2012 11:08:12 +1000 From:
>>>> skippy.hammond at gmail.com To: i_pelvan at hotmail.com CC:
>>>> python-win32 at python.org Subject: Re: [python-win32] Silent
>>>> crashes in calls to a COM object
>>> in Python
>>>> Python and pywin32 don't impose any time limits for timeouts
>>>> and I can't think of what could cause this other than (say) an
>>>> exception handler in your script that ignores exceptions and
>>>> terminates the process. Even if Python actually crashed I'd
>>>> expect Windows to show the "app crashed" dialog. If you have
>>>> MSVC you could try running the python process under it to see
>>>> if it reports anything strange.
>>>> Mark
>>>> On 24/04/2012 8:09 AM, Deniz Pelvan wrote:
>>>>> Hello guys,I am having trouble with the Python interpreter
>>>>> crashing silently (no exceptions or errors thrown) when I
>>>>> make a call to a very CPU-intensive method in my COM/ATL
>>>>> component using Pywin32. The method is an FFT analysis for
>>>>> audio files and hits about 25% CPU on a single core and runs
>>>>> for about 1 minutes. I have tested the COM method intensively
>>>>> via normal win32 applications and there are no problems with
>>>>> it (I can run the same method over and over again 1000s of
>>>>> times in a win32 app).- Also the same Python script (with a
>>>>> call to this COM method) will run successfully on different
>>>>> machines and will fail at the same machine only randomly
>>>>> (i.e. on some machines, it never fails, while on others, it
>>>>> has ~50% failure rate). - This specific method is the most
>>>>> CPU-intensive one in the COM component and other methods do
>>>>> not fail on any of the machines. Because of this, I think the
>>>>> problem might have something to do with either the CPU usage
>>>>> or a timeout feature on Python or pywin32. Are there any
>>>>> tools that would help me narrow down the cause or maybe
>>>>> increase the CPU/time limits for Python/PyWin32? I haven't
>>>>> seen anything in the documentation that'd help.Thanks in
>>>>> advanceDeniz Pelvan
>>>>> _______________________________________________ python-win32
>>>>> mailing list python-win32 at python.org
>>>>> http://mail.python.org/mailman/listinfo/python-win32
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