Right way to initialize python embedded in a multi-threaded application
francis.brosnan at gmail.com
francis.brosnan at gmail.com
Sat May 11 14:23:55 EDT 2013
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 ();
PyEval_InitThreads();
/* 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 */
PyEval_ReleaseLock ();
<<and now, from other threads, use>>
/* wait til gil acquired */
state = PyGILState_Ensure();
/* your code */
/* release GIL */
PyGILState_Release (state);
Hope it helps, Cheers!
> I'm embedding python in a multi-threaded C application.
>
> I've taken care to wrap every call to the Python C API with
>
>
>
> gstate = PyGILState_Ensure();
>
> // call python code
>
> PyGILState_Release(gstate);
>
>
>
> But I'm stumped with what to do in the initialization.
>
> Right after the call to Py_IsInitialized() I've added a call:
>
>
>
> PyEval_InitThreads();
>
>
>
> The docs say that this function leaves the GIL locked when it returns.
>
> I do some more initializations like importing modules and then I call
>
>
>
> PyEval_ReleaseLock();
>
>
>
> This seems to cause a problem since not long after a call to
>
> PyGILState_Release(gstate) that's made in a different thread crashes.
>
> with
>
>
>
> "Fatal Python error: This thread state must be current when releasing"
>
>
>
> If I don't do the call to PyEval_ReleaseLock() in the main thread
>
> right after initialization, the GIL seems to be released
>
> after the first PyGILState_Ensure() - PyGILState_Release() pair.
>
>
>
> So what am I doing wrong here?
>
> What is the correct way of initializing a multi-threaded application?
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