Move code to init Python GIL/threads into separate C file to avoid compiler deprecation warnings

Signed-off-by: Christopher Arndt <[email protected]>

Author: SpotlightKid

MANIFEST.in

@@ -6,6 +6,7 @@ include tox.ini
 include *.rst
 include src/_rtmidi.pyx
 include src/_rtmidi.cpp
+include src/pyinit.h
 include src/rtmidi/RtMidi.cpp
 include src/rtmidi/RtMidi.h
 

src/_rtmidi.pyx

@@ -131,13 +131,10 @@ else:
     string_types = (str,)
 
 
-# Init Python threads and GIL, because RtMidi calls Python from native threads.
-# See http://permalink.gmane.org/gmane.comp.python.cython.user/5837
-cdef extern from "Python.h":
-    void PyEval_InitThreads()
-
-PyEval_InitThreads()
+cdef extern from "pyinit.h":
+    void py_init()
 
+py_init()
 
 # Declarations for RtMidi C++ classes and their methods we use
 

src/pyinit.h

@@ -0,0 +1,22 @@
+#include <Python.h>
+/*
+ * This code initializes Python threads and GIL, because RtMidi calls Python
+ * from native threads.
+ *
+ * See http://permalink.gmane.org/gmane.comp.python.cython.user/5837
+ *
+ * *PyEval_InitThreads* is a no-op since Python.37 and deprecated since
+ * Python 3.6. Now *Py_Initialize* initializes the GIL.
+ *
+ * The calls are in this separate C file instead of in the main .pyx file so
+ * that we can use pre-compiler conditionals and don't get a compiler
+ * deprecation warning on Python 3.9+ for including *PyEval_InitThreads*.
+ */
+
+void py_init() {
+    #if PY_MAJOR_VERSION >= 3 and PY_MINOR_VERSION >= 7
+        Py_Initialize();
+    #else
+        PyEval_InitThreads();
+    #endif
+}