Use TLS for the PyThreadState pointer instead of a field on Connection; this allows a Connection to be used safely in multiple threads concurrently
diff --git a/src/ssl/connection.h b/src/ssl/connection.h
index dedb73e..13f42f0 100644
--- a/src/ssl/connection.h
+++ b/src/ssl/connection.h
@@ -42,7 +42,7 @@
     SSL                 *ssl;
     ssl_ContextObj      *context;
     PyObject            *socket;
-    PyThreadState       *tstate;
+    PyThreadState       *tstate; /* This field is no longer used. */
     PyObject            *app_data;
 } ssl_ConnectionObj;