gh-117783: Immortalize objects that use deferred reference counting (#118112)

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.

1 files changed, 19 insertions, 0 deletions

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 70d2610..15f6543 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -516,6 +516,25 @@ def has_no_debug_ranges():
 def requires_debug_ranges(reason='requires co_positions / debug_ranges'):
     return unittest.skipIf(has_no_debug_ranges(), reason)
 
+@contextlib.contextmanager
+def suppress_immortalization(suppress=True):
+    """Suppress immortalization of deferred objects."""
+    try:
+        import _testinternalcapi
+    except ImportError:
+        yield
+        return
+
+    if not suppress:
+        yield
+        return
+
+    old_values = _testinternalcapi.set_immortalize_deferred(False)
+    try:
+        yield
+    finally:
+        _testinternalcapi.set_immortalize_deferred(*old_values)
+
 MS_WINDOWS = (sys.platform == 'win32')
 
 # Is not actually used in tests, but is kept for compatibility.