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-   -   Re: Embedding Python in multi-threaded app (http://www.velocityreviews.com/forums/t322019-re-embedding-python-in-multi-threaded-app.html)

Harri Pesonen 09-04-2003 01:11 PM

Re: Embedding Python in multi-threaded app
 
I solved it. Downloaded the PyWM source code (http://pywx.idyll.org/)
and checked how it does it. Even if it is linux code, my Win32
application started working (or in fact stopping) correctly.

The correct startup sequence is:

Py_Initialize();
PyEval_InitThreads();
mainState = PyThreadState_Swap(NULL);
PyEval_ReleaseLock();

And the correct cleanup sequence is:

PyEval_AcquireLock();
PyThreadState_Swap(mainState);
PyEval_ReleaseLock();
Py_Finalize();

I don't understand why

mainState = PyThreadState_Swap(NULL);
and
PyThreadState_Swap(mainState);
PyEval_ReleaseLock();

are needed, so if someone can explain? :-)

Harri

Harri.Pesonen@wicom.com (Harri Pesonen) wrote in message news:<17fbc98a.0309040028.6776d426@posting.google. com>...
> Hello. Thanks to the message below
> (http://groups.google.fi/groups?selm=...%40netcom.com),
> I was able to do the same, almost. I have currently only one problem.
> When I call Py_Finalize() when the dll terminates, it crashes. I have
> Python 2.3. Everything else works, I have run many different scripts
> in threads. I wonder if someone has noticed anything similar, and
> perhaps found a solution.
>
> Also I don't understand PyThreadState_Swap(interp) call below, but it
> does not work properly without it, the thread termination hangs
> without it. The documentation says that Py_NewInterpreter() already
> makes the new state current.
>
> Thanks for any help!
>
> Harri
>
> --- Original message below ----
>
> Thanks for comments from Guido. I have a very preliminary version
> working with Python embedded in a multi-threaded C++ application.
>
> I'd like to summarize what I'm doing so that others will have an
> example to follow or so that someone can correct me if I'm still
> doing something wrong.
>
> My application creates multiple threads, one for each end-user
> session. I create a separate Python sub-interpreter for each thread
> (session), then evaluate scripts in that session with the
> sub-interpreter for that session. I do this so that within a
> session, scripts are evaluated under a context/environment local to
> that session and so that the scripts in a session do not share
> (borrow or steal) global values, imported functions, etc from other
> sessions. Thus, my users (who are developing Python scripts) can
> write scripts from the viewpoint that the scripts for each session
> will run in their own little world under their own separate
> environment. I view this as a very important benefit that embedded
> Python gives me.
>
> Here is a summary of my latest code:
>
> // At the very beginning of the application.
> Py_Initialize();
> PyEval_InitThreads();
> PyEval_ReleaseLock();
> o
> o
> o
> // Here we are in the constructor for a session.
> PyEval_AcquireLock();
> interp = Py_NewInterpreter();
> // Note that this application has multiple threads.
> // It maintains a separate interp (sub-interpreter) for each thread.
> PyThreadState_Swap(interp);
> // Call some Python C/API functions here
> PyEval_ReleaseThread(interp);
> o
> o
> o
> // Get sub-interpreter for current thread.
> interp = ...
> PyEval_AcquireThread(interp);
> // Call more Python C/API functions here, e.g. PyRun_SimpleString
> PyEval_ReleaseThread(interp);
> o
> o
> o
> // Get sub-interpreter for current thread.
> interp = ...
> PyEval_AcquireThread(interp);
> // Call more Python C/API functions here
> PyEval_ReleaseThread(interp);
> o
> o
> o
> // Here we are in the destructor for a session.
> // Get sub-interpreter for current thread.
> interp = ...
> PyEval_AcquireThread(interp);
> Py_EndInterpreter(interp);
> PyEval_ReleaseLock();
> o
> o
> o
> // At the very end of the application.
> PyEval_AcquireLock();
> Py_Finalize();
>
>
> Thanks again for help. And I hope that this can serve as a simple
> model for others trying to embed Python in a multi-threaded
> application.
>
> -- Dave
>
>
>
> Guido van Rossum <guido@CNRI.Reston.VA.US> wrote:
>
> > Yes, but this is still dangerous. You should really use the APIs that
> > manage the lock *and* the thread state: use
> > PyEval_AcquireThread() and PyEval_ReleaseThread(). (The argument to
> > the latter should be the current thread state, gotten from
> > PyThreadState_Get().)
> > In case you're inclined to continue this while I'm unavailable, read
> > the source -- e.g. the routines I mentioned here are in
> > Python/ceval.c.
> > --Guido van Rossum (home page: http://www.python.org/~guido/)



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