gh-113964: Don't prevent new threads until all non-daemon threads exit (#116677)

Starting in Python 3.12, we prevented calling fork() and starting new threads
during interpreter finalization (shutdown). This has led to a number of
regressions and flaky tests. We should not prevent starting new threads
(or `fork()`) until all non-daemon threads exit and finalization starts in
earnest.

This changes the checks to use `_PyInterpreterState_GetFinalizing(interp)`,
which is set immediately before terminating non-daemon threads.

1 files changed, 1 insertions, 1 deletions

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 6889e8f..4912cd7 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -1729,7 +1729,7 @@ do_start_new_thread(thread_module_state *state, PyObject *func, PyObject *args,
                         "thread is not supported for isolated subinterpreters");
         return -1;
     }
-    if (interp->finalizing) {
+    if (_PyInterpreterState_GetFinalizing(interp) != NULL) {
         PyErr_SetString(PyExc_PythonFinalizationError,
                         "can't create new thread at interpreter shutdown");
         return -1;