[3.13] gh-124984: Enhance ssl thread safety (GH-124993) (#125780)

Make SSL objects thread safe in Free Theaded build by
using critical sections.

(cherry picked from commit 4c53b25775)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Lib/test/test_ssl.py

@@ -3,6 +3,8 @@
 import sys
 import unittest
 import unittest.mock
+from ast import literal_eval
+from threading import Thread
 from test import support
 from test.support import import_helper
 from test.support import os_helper
@@ -304,11 +306,19 @@ def test_wrap_socket(sock, *,
     return context.wrap_socket(sock, **kwargs)
 
 
+USE_SAME_TEST_CONTEXT = False
+_TEST_CONTEXT = None
+
 def testing_context(server_cert=SIGNED_CERTFILE, *, server_chain=True):
     """Create context
 
     client_context, server_context, hostname = testing_context()
     """
+    global _TEST_CONTEXT
+    if USE_SAME_TEST_CONTEXT:
+        if _TEST_CONTEXT is not None:
+            return _TEST_CONTEXT
+
     if server_cert == SIGNED_CERTFILE:
         hostname = SIGNED_CERTFILE_HOSTNAME
     elif server_cert == SIGNED_CERTFILE2:
@@ -326,6 +336,10 @@ def testing_context(server_cert=SIGNED_CERTFILE, *, server_chain=True):
     if server_chain:
         server_context.load_verify_locations(SIGNING_CA)
 
+    if USE_SAME_TEST_CONTEXT:
+        if _TEST_CONTEXT is not None:
+            _TEST_CONTEXT = client_context, server_context, hostname
+
     return client_context, server_context, hostname
 
 
@@ -2834,6 +2848,44 @@ class ThreadedTests(unittest.TestCase):
                 'Cannot create a client socket with a PROTOCOL_TLS_SERVER context',
                 str(e.exception))
 
+    @unittest.skipUnless(support.Py_GIL_DISABLED, "test is only useful if the GIL is disabled")
+    def test_ssl_in_multiple_threads(self):
+        # See GH-124984: OpenSSL is not thread safe.
+        threads = []
+
+        global USE_SAME_TEST_CONTEXT
+        USE_SAME_TEST_CONTEXT = True
+        try:
+            for func in (
+                self.test_echo,
+                self.test_alpn_protocols,
+                self.test_getpeercert,
+                self.test_crl_check,
+                self.test_check_hostname_idn,
+                self.test_wrong_cert_tls12,
+                self.test_wrong_cert_tls13,
+            ):
+                # Be careful with the number of threads here.
+                # Too many can result in failing tests.
+                for num in range(5):
+                    with self.subTest(func=func, num=num):
+                        threads.append(Thread(target=func))
+
+            with threading_helper.catch_threading_exception() as cm:
+                for thread in threads:
+                    with self.subTest(thread=thread):
+                        thread.start()
+
+                for thread in threads:
+                    with self.subTest(thread=thread):
+                        thread.join()
+                if cm.exc_value is not None:
+                    # Some threads can skip their test
+                    if not isinstance(cm.exc_value, unittest.SkipTest):
+                        raise cm.exc_value
+        finally:
+            USE_SAME_TEST_CONTEXT = False
+
     def test_getpeercert(self):
         if support.verbose:
             sys.stdout.write("\n")