Python, COM Servers, and Multi-Threading

[Steve Holden]

Carl Waldbieser wrote:
> I have been considering using Python and the Reportlab library for
> generating PDF reports for the back-end of a web based application.  The
> application runs most of its background tasks on a dedicated server that is
> Windows based (Win2K or Win2k3).  The program that launches the tasks
> requires a COM-based interface, so I wrote a Python COM server using Mark
> Hammond's PythonCom libraries and import and run the reporlab modules from
> there.
> 
Have you selected a specific threading model for your COM server? This 
will affect how hardware resource are allocated as well as how sharing 
takes place between different uses.

> I had been reading up on Python and it's handling of the multiple threads,
> specifically the Global Interpreter Lock (GIL).  I got to wondering if a
> multi-processor machine machine would be able to take advantage of its
> extra processing power using this setup.  I am guessing that the GIL is
> global with respect to each instance of a running Python interpreter, so if
> say 4 interpreters were running, a 4 processor machine would be able to
> take advantage of this.  However, I am not quite sure how launching my
> reports via COM behaves-- if I launched 4 reports this way, would that be
> like launching 4 seperate instances of the Python interpreter, or would it
> be just a single instance, and therefore run into the limitations of the
> GIL?  If so, can anybody offer suggestions as to a design that would be
> better able to take advantage of a multi-processor machine?
> 
I am certainly no expert on COM threading models, but I would suspect 
that if you specify you want your COM server to be in-process then you 
would get a per-process interpreter.

You also need to be aware that if you trigger this stuff with IIS then 
the web server itself performs thread pooling and (I believe) allocates 
only one process per "application", so this may defeat your desire to 
use all four processors concurrently.

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
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