Need some help with Python/C api and threading
steve.menard at videotron.ca
Thu Jun 17 19:45:53 CEST 2004
Les Smithson wrote:
>>>>>>"Steve" == Steve Menard <steve.menard at videotron.ca> writes:
> I haven't done this for a while and I'm a little hazy on it, so this
> may be incorrect:
> I used 'PyThreadState *ts = Py_NewInterpreter();' to set a new
> sub-interpreter state if called in a new thread.
> If the embedded script calls back into the extension, it restores that
> thread state and acquires the GIL before making any other Py* calls by
> calling 'PyEval_RestoreThread(ts);'. Before returning, it calls
Thanks, however I dont think thid will work. The doc for
Py_NewInterpreter says that it created a "an (almost) totally separate
environment for the execution of Python code. In particular, the new
interpreter has separate, independent versions of all imported modules".
This is not good for me, as the callbacks must come in the "main"
Is there a tutorial somewhere? Or a particularly well written extension
module whose source code I could take a look at?
Let me summarize my situation :
I am writing a python extension, not embedding python. As such, I have
no control over the interpreter, or the threads.
The library I am embedding is not of my own writing. It can create any
number of threads. It can make callbacks into the Python interpreter on
any such thread.
A given thread can original either in python or the library, but control
can go back and forth : A python method can call a library method, which
in turn calls back into python, which calls a linrary method, etc ...
This is a potential problem, because trying to grab in GIL twice from
the same thread will cause a deadlock.
So far, here is what I am doing (without success).
1) In the init_XXX method, I call PyEval_InitThreads().
2) Every time I pass control to the library, I wrap the call into a
Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS pair. Note that I adde this
recently, and get an error the second time Py_BEGIN_ALLOW_THREADS is
called, with the following error "Fatal Python error: PyEval_SaveThread:
3) Finally, whenever I receive a callback from the library, I added
these lines to the start and end of the method :
PyInterpreterState* interp = PyInterpreterState_New();
PyThreadState *tstate = PyThreadState_New(interp);
Thats about it. I am sure someone, somewhere has done what I need :(
Thanks for any help you can provide,
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