Hello, this is my first python bug report!

I've been running builds of Python 3.7.x on CentOS Linux release 7.7 (64bit/Intel Core
2 Duo) 
and I ran into hangs with test_ssl.py when using latest SSL 1.1.1d sources.

I've done a full compilation from source for Python 3.7.7 and SSL 1.1 in my
workspaces.

From what I can tell the problem is when SSL 1.1 is built with no threading
there is no locking enabled by python.

This one line change will make the hangs in test_ssl.py  go away:

Index: Modules/_ssl.c

--- Modules/_ssl.c      (revision 70)
+++ Modules/_ssl.c      (working copy)
@@ -5875,7 +5875,7 @@
     if (!_setup_ssl_threads()) {
         return NULL;
     }
-#elif OPENSSL_VERSION_1_1 && defined(OPENSSL_THREADS)
+#elif OPENSSL_VERSION_1_1
     / OpenSSL 1.1.0 builtin thread support is enabled /
     _ssl_locks_count++;

# endif

There appears to be an assumption in _ssl.c and test_ssl.y that SSL 1.1 will be
threaded
but this may not be true (as in my case).

Appreciate any feedback. Thanks!

How did you build OpenSSL 1.1.1d? Python assumes default build of OpenSSL. Since Python is now always multi-threaded we no longer support non-threaded OpenSSL builds.

I built with 'no-threads' option.
I understand if you no longer wish to support non-threaded SSL. 
But it just seemed to me that you could if you protected the SSL API calls with locking since I can get all your ssl tests to work with this minor change.

It not about what I wish or wish not to do.

Python requires thread-safe libraries. A library without proper locking and thread safety is no longer safe to use without great effort and careful locking in the glue code. A non-threaded OpenSSL build will lead to memory corruption and eventually crash the interpreter.

New changeset c087a268a4d4ead8ef2ca21e325423818729da89 by Christian Heimes in branch 'master':
bpo-40515: Require OPENSSL_THREADS (GH-19953)
https://github.com/python/cpython/commit/c087a268a4d4ead8ef2ca21e325423818729da89

New changeset 387c7441f589cc45ea86f1fa257af616c39d9a4b by Christian Heimes in branch '3.8':
[3.8] bpo-40515: Require OPENSSL_THREADS (GH-19953) (GH-20119)
https://github.com/python/cpython/commit/387c7441f589cc45ea86f1fa257af616c39d9a4b

New changeset efc9065904c4df8962e04303c2c03642f45019b5 by Christian Heimes in branch '3.7':
[3.7] bpo-40515: Require OPENSSL_THREADS (GH-19953) (GH-20120)
https://github.com/python/cpython/commit/efc9065904c4df8962e04303c2c03642f45019b5

Users will now get an error message when they are trying to compile against an OpenSSL build without thread support.