[3.13] gh-117657: Fix race involving immortalizing objects (GH-119927) (#120005)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see gh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.

(cherry picked from commit 47fb4327b5c405da6df066dcaa01b7c1aefab313)

1 files changed, 5 insertions, 9 deletions

diff --git a/Include/internal/pycore_gc.h b/Include/internal/pycore_gc.h
index 6058252..ba8b8e1 100644
--- a/Include/internal/pycore_gc.h
+++ b/Include/internal/pycore_gc.h
@@ -347,15 +347,11 @@ struct _gc_runtime_state {
 
     /* gh-117783: Deferred reference counting is not fully implemented yet, so
        as a temporary measure we treat objects using deferred referenence
-       counting as immortal. */
-    struct {
-        /* Immortalize objects instead of marking them as using deferred
-           reference counting. */
-        int enabled;
-
-        /* Set enabled=1 when the first background thread is created. */
-        int enable_on_thread_created;
-    } immortalize;
+       counting as immortal. The value may be zero, one, or a negative number:
+        0: immortalize deferred RC objects once the first thread is created
+        1: immortalize all deferred RC objects immediately
+        <0: suppressed; don't immortalize objects */
+    int immortalize;
 #endif
 };