Re: Multi-threaded wrapping

the "-threads" option tells SWIG to release the GIL before entering 
wrapped C++ code. This lets Python interpreter to continue to run while 
the wrapped C++ code executes. However, this means that any calls made 
into the Python C-API initiated from your wrapped code must first 
acquire the "GIL" to prevent the interpreter state from becoming 
corrupted. Of course you also need release GIL when done calling into 
the Python C-API. That's pretty much all there is to it.

For more info see:

https://docs.python.org/3/c-api/init.html#thread-state-and-the-global-interpreter-lock
https://www.swig.org/Doc4.0/Python.html#Python_multithreaded

Also may be instructive to look at the code SWIG generates when you add 
the -threads option. You can grep for the word THREAD in the C++ code 
SWIG spits out.

Hope this helps


On 9/19/22 09:48, William S Fulton wrote:
>
>
> On Mon, 12 Sept 2022 at 18:55, Rob McDonald <[email protected]> 
> wrote:
>
>     I have a C++ application with an event driven GUI (using FLTK)
>     that is currently wrapped with Swig for Python.
>
>     I can make calls (with no GUI loaded) to the exposed API.  I can
>     also launch the GUI from Python (and FLTK event loop) and interact
>     with the graphical program for a while -- when satisfied, I can
>     terminate the event loop to return control to Python.
>
>     I would like to be able to leave the application GUI active (event
>     loop still running) and return control to Python.  The Python side
>     might actually be a separate GUI with its own event loop.  The two
>     loops will need to communicate occasionally -- I can likely
>     initiate all communication from the Python side.
>
>     I believe I will need to run Swig with the 'threads' option.  I
>     also need to set up some sort of lock so the C++ event loop pauses
>     when the C++ API is responding to a request from the Python side.
>
>     Can anyone give any pointers on how to achieve this? Are there any
>     examples of this available online?
>
>
> There is an example of the 'threads' option in the SWIG test-suite. 
> See 
> https://github.com/swig/swig/blob/master/Examples/test-suite/python_threads.i 
> with associated runtime test 
> https://github.com/swig/swig/blob/master/Examples/test-suite/python/python_threads_runme.py. 
> That's all I can find.
>
> William
>
>
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