[python-win32] Dispatch vs EnsureDispatch performance

[Mark Hammond]

On 2024-07-17 10:30 a.m., Sven Bardos via python-win32 wrote:

> Hi Mark,
>
> I found some time to debug and profile my issue a little bit more.
> In my scenario I call a COM method which returns a list of 14195 
> integers plus the amount of the found objects.
>
> If I profile that call I get the following:
>
> ncalls  tottime  percall  cumtime  percall filename:lineno(function)
> ...
> 1    0.000    0.000    0.025    0.025 __init__.py:572(_ApplyTypes_)
> 1    0.000    0.000    0.007    0.007 __init__.py:603(_get_good_object_)
> 14195    0.001    0.000    0.001    0.000 
> __init__.py:608(_get_good_single_object_)
> 14198/1    0.005    0.000    0.007    0.007 
> __init__.py:614(_get_good_object_)
> ...
>
> So _get_good_object_ is called ~14200 times.
> If I do that in a loop 100x, I get an execution time of ~3.3s
>
> If I change the code in the _ApplyTypes_ function to:
>
> def _ApplyTypes_(self, dispid, wFlags, retType, argTypes, user, 
> resultCLSID, *args):
> return self._oleobj_.InvokeTypes(dispid, 0, wFlags, retType, argTypes, 
> *args)
> # return self._get_good_object_(
> #     self._oleobj_.InvokeTypes(dispid, 0, wFlags, retType, argTypes, 
> *args),
> #     user,
> #     resultCLSID,
> # )
>
> that is, avoiding the _get_good_object_() calls, the execution time is 
> ~1.6s for 100 iterations. Which is ~50% of the original time. The 
> result is the same, in this case.

I'm certainly up for looking at optimizations to how this works, but I 
don't think it's as simple as not calling the function - there are cases 
where it would return different objects. I don't think an instance 
method is needed (ie, maybe we could just call the final implementation 
and maybe even inline some of those calls, but if you say the result is 
identical, it looks a little like there are just 2 isinstance() calls 
which return False in this scenario, so maybe this might also offer 
optimization ideas (eg, if the type in question for your examples are 
builtin types like int/string/etc, maybe these could be checked before 
making any other calls?).

HTH,

Mark

>
> Do you have any thoughts on this?
>
> Best regards,
> Sven
>
> Am Mi., 17. Apr. 2024 um 17:19 Uhr schrieb Mark Hammond 
> <skippy.hammond at gmail.com>:
>
>     I'm mildly surprised by that - a profiler might show some
>     low-hanging fruit, and/or might show different characteristics
>     when many more functions are used. However, the primary reason for
>     EnsureDispatch is for better support of the object model - there's
>     far more context available and this less chance of upsetting some
>     COM objects - eg, when `foo.bar` is seen, EnsureDispatch knows for
>     sure that `bar` is a method, but dynamic dispatch doesn't know if
>     the resulting object is going to be called or not.
>
>     HTH,
>
>     Mark
>
>     On 2024-04-17 2:07 a.m., Sven Bardos via python-win32 wrote:
>>     Hi,
>>
>>     shouldn't be EnsureDispatch be faster than Dispatch once the code
>>     generation is done?
>>
>>     I've measured it by calling 6000 COM calls like this:
>>
>>     dirpath = Path('C:/Users/sbardos/AppData/Local/Temp/gen_py/3.10/')
>>     if dirpath.exists() and dirpath.is_dir():
>>     shutil.rmtree(dirpath)
>>
>>     app = Dispatch("CT.Application")
>>     job = app.CreateJobObject()
>>
>>     start = timer()
>>
>>     for i in range(2000):
>>     cnt, devIds = job.GetAllDeviceIds()
>>     cnt, sheetIds = job.GetSheetIds()
>>     dev = job.CreateDeviceObject()
>>
>>     end = timer()
>>     print(f"Time ellapsed (late): {end - start}s")
>>     and the ensure Dispatch version:
>>     app = EnsureDispatch("CT.Application")
>>     job = app.CreateJobObject()
>>     start = timer()
>>     for i in range(2000):
>>     cnt, devIds = job.GetAllDeviceIds(None)
>>     cnt, sheetIds = job.GetSheetIds(None)
>>     dev = job.CreateDeviceObject()
>>     end = timer()
>>     print(f"Time ellapsed (early): {end - start}s")
>>     EnsureDispatch is a little bit slower ~4.2s compared to ~4.0s.
>>     If I don't get a performance boost with EnsureDispatch, is there
>>     even a point using it?
>>
>>     Thanks,
>>     Sven
>>
>>     _______________________________________________
>>     python-win32 mailing list
>>     python-win32 at python.org
>>     https://mail.python.org/mailman/listinfo/python-win32
>
>
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