Caveat on GIL

There is a caveat to remember when using gil. In our callbacks, we need to acquire the GIL on each callback before we call any Python code; otherwise, we will segfault and get really confused. So, if you look into each of the libevent callbacks when calling the Cython functions, you have the following:

 PyGILState_STATE gilstate_save = PyGILState_Ensure();
 readcb (client, (char *)data);
 PyGILState_Release(gilstate_save);

Notice that this is also called on the other two callbacks—firstly on the discb callback:

  PyGILState_STATE gilstate_save = PyGILState_Ensure();
  discb (client, NULL);
  PyGILState_Release(gilstate_save);

Finally, on the connect callback, we must be a little safer and call it this way:

 PyGILState_STATE gilstate_save = PyGILState_Ensure();
  if (!conncb (NULL, inet_ntoa (client_addr.sin_addr)))
    {
…
    }
 else
    close (client_fd);
  PyGILState_Release(gilstate_save);

We have to do this since we executed this with nogil from Cython. We need to acquire gil...