gh-123022: Fix crash with `Py_Initialize` in background thread (#123052)

Check that the current default heap is initialized in
`_mi_os_get_aligned_hint` and `mi_os_claim_huge_pages`.

The mimalloc function `_mi_os_get_aligned_hint` assumes that there is an
initialized default heap. This is true for our main thread, but not for
background threads. The problematic code path is usually called during
initialization (i.e., `Py_Initialize`), but it may also be called if the
program allocates large amounts of memory in total.

The crash only affected the free-threaded build.

1 files changed, 8 insertions, 1 deletions

diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index aab4333..7860c67 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -1,6 +1,6 @@
 # Run the tests in Programs/_testembed.c (tests for the CPython embedding APIs)
 from test import support
-from test.support import import_helper, os_helper, MS_WINDOWS
+from test.support import import_helper, os_helper, threading_helper, MS_WINDOWS
 import unittest
 
 from collections import namedtuple
@@ -1802,6 +1802,13 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
 
         self.assertEqual(out, expected)
 
+    @threading_helper.requires_working_threading()
+    def test_init_in_background_thread(self):
+        # gh-123022: Check that running Py_Initialize() in a background
+        # thread doesn't crash.
+        out, err = self.run_embedded_interpreter("test_init_in_background_thread")
+        self.assertEqual(err, "")
+
 
 class SetConfigTests(unittest.TestCase):
     def test_set_config(self):