Release the GIL in accelerated functions.

Release the GIL so that we can do other stuff in Python threads, but be careful not to do expensive operations or it might slow down the accelerated functions (even though they run in separate OS threads).

src/accelerated_functions.c

@@ -148,7 +148,13 @@ static PyObject *py_push_data(PyObject *self, PyObject *args){
 		return NULL;
 	}
 	//
-	int ret_val = push_data(socket, bytes_total, buffer, buffer_len);
+	int ret_val;
+	Py_BEGIN_ALLOW_THREADS
+	// GIL is unlocked, but don't do expensive operations in
+	// other threads or it might slow this one down
+	ret_val = push_data(socket, bytes_total, buffer, buffer_len);
+	Py_END_ALLOW_THREADS
+	//
 	PyObject* py_ret_val = PyLong_FromLong(ret_val);
 	//
 	return py_ret_val;
@@ -165,7 +171,13 @@ static PyObject *py_pull_data(PyObject *self, PyObject *args){
 	}
 	//
 	double elapsed_time = 0;
-	int ret_val = pull_data(socket, bytes_total, buffer_len, &elapsed_time);
+	int ret_val;
+	Py_BEGIN_ALLOW_THREADS
+	// GIL is unlocked, but don't do expensive operations in
+	// other threads or it might slow this one down
+	ret_val = pull_data(socket, bytes_total, buffer_len, &elapsed_time);
+	Py_END_ALLOW_THREADS
+	//
 	PyObject* py_ret_val = Py_BuildValue("(id)", ret_val, elapsed_time);
 	//
 	return py_ret_val;