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, 18 insertions, 0 deletions

diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 2c726c9..e341f0c 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -8,6 +8,7 @@
 #include <Python.h>
 #include "pycore_initconfig.h"    // _PyConfig_InitCompatConfig()
 #include "pycore_runtime.h"       // _PyRuntime
+#include "pycore_pythread.h"      // PyThread_start_joinable_thread()
 #include "pycore_import.h"        // _PyImport_FrozenBootstrap
 #include <inttypes.h>
 #include <stdio.h>
@@ -2022,6 +2023,22 @@ static int test_init_main_interpreter_settings(void)
     return 0;
 }
 
+static void do_init(void *unused)
+{
+    _testembed_Py_Initialize();
+    Py_Finalize();
+}
+
+static int test_init_in_background_thread(void)
+{
+    PyThread_handle_t handle;
+    PyThread_ident_t ident;
+    if (PyThread_start_joinable_thread(&do_init, NULL, &ident, &handle) < 0) {
+        return -1;
+    }
+    return PyThread_join_thread(handle);
+}
+
 
 #ifndef MS_WINDOWS
 #include "test_frozenmain.h"      // M_test_frozenmain
@@ -2211,6 +2228,7 @@ static struct TestCase TestCases[] = {
     {"test_get_argc_argv", test_get_argc_argv},
     {"test_init_use_frozen_modules", test_init_use_frozen_modules},
     {"test_init_main_interpreter_settings", test_init_main_interpreter_settings},
+    {"test_init_in_background_thread", test_init_in_background_thread},
 
     // Audit
     {"test_open_code_hook", test_open_code_hook},