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    <p>There are a few things you need to do if you are invoking a Python function from a C/C++ callback. First when you save off your python function object, you need to increment the reference count with:</p> <pre><code>Py_INCREF(pFunc) </code></pre> <p>Otherwise Python has no idea you are holding onto an object reference, and it may garbage collect it, resulting in a segmentation fault when you try to use it from your callback.</p> <p>Then next thing you need to be concerned about is what thread is running when your C/C++ callback is invoked. If you are getting called back from another non-Python created thread (i.e. a C/C++ thread receiving data on a socket), then you <strong>MUST</strong> acquire Python's Global Interpreter Lock (GIL) before calling any Python API functions. Otherwise your program's behavior is undefined. To acquire the GIL you do:</p> <pre><code>void callback() { PyGILState_STATE gstate; gstate = PyGILState_Ensure(); // Get args, etc. // Call your Python function object PyObject * pInstance = PyObject_CallObject(pFunc, args); // Do any other needed Python API operations // Release the thread. No Python API allowed beyond this point. PyGILState_Release(gstate); } </code></pre> <p>Also, in your extension module's init function, you should do the following to ensure that threading is properly initialized:</p> <pre><code>// Make sure the GIL has been created since we need to acquire it in our // callback to safely call into the python application. if (! PyEval_ThreadsInitialized()) { PyEval_InitThreads(); } </code></pre> <p>Otherwise, crashes and strange behavior may ensue when you attempt to acquire the GIL from a non-Python thread.</p> <p>See <a href="http://docs.python.org/2/c-api/init.html#thread-state-and-the-global-interpreter-lock" rel="noreferrer">Non-Python Created Threads</a> for more detail on this.</p>
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    1. COThanks a lot. :) That was the exact problem.
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