Right way to initialize python embedded in a multi-threaded application

[francis.brosnan at gmail.com]

Just clarify there's no problem about calling twice to PyEval_InitThreads ()
as indicated by Python's doc.

> Hi,
> 
> 
> 
> Maybe you already fixed the issue, but for the record, I've got the same
> 
> problem and finally it turned out that I was calling PyEval_InitThreads twice
> 
> and also after fixing that, I also had to move the call to PyEval_ReleaseLock();  at the end of the entire initialization (not just after PyEval_initThreads).
> 
> 
> 
> The key thing there is to follow:
> 
> 
> 
> <<at initialization thread>>
> 
> Py_Initialize ();
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> PyEval_InitThreads(); 
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> /* now call here to initialize all python code by loading external files 
> 
>    or internal module loading (i.e. Py_InitModule3) */
> 
> /* ..and now, once no more Python C/API call is required, release
> 
>    the GIL so other threads can come into play */
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> PyEval_ReleaseLock ();
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> 
> 
> <<and now, from other threads, use>>
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> /* wait til gil acquired */
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> state  = PyGILState_Ensure();
> 
> /* your code */
> 
> /* release GIL */
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> PyGILState_Release (state);
> 
> 
> 
> Hope it helps, Cheers!
> 
> 
> 
> 
> 
> > I'm embedding python in a multi-threaded C application.
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> > 
> 
> > I've taken care to wrap every call to the Python C API with
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> > 
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> > 
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> > 
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> > gstate = PyGILState_Ensure();
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> > 
> 
> > // call python code
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> > 
> 
> > PyGILState_Release(gstate);
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> > 
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> > 
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> > 
> 
> > But I'm stumped with what to do in the initialization.
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> > 
> 
> > Right after the call to Py_IsInitialized() I've added a call:
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> > 
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> > 
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> > 
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> > PyEval_InitThreads();
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> > 
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> > 
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> > 
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> > The docs say that this function leaves the GIL locked when it returns.
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> > 
> 
> > I do some more initializations like importing modules and then I call
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> > 
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> > 
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> > 
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> > PyEval_ReleaseLock();
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> > 
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> > 
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> > 
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> > This seems to cause a problem since not long after a call to
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> > 
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> > PyGILState_Release(gstate) that's made in a different thread crashes.
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> > 
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> > with
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> > 
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> > 
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> > 
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> > "Fatal Python error: This thread state must be current when releasing"
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> > 
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> > 
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> > 
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> > If I don't do the call to PyEval_ReleaseLock() in the main thread
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> > 
> 
> > right after initialization, the GIL seems to be released
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> > 
> 
> > after the first PyGILState_Ensure() - PyGILState_Release() pair.
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> > 
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> > 
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> > 
> 
> > So what am I doing wrong here?
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> > 
> 
> > What is the correct way of initializing a multi-threaded application?