gh-122697: Fix free-threading memory leaks at shutdown

Misc/NEWS.d/next/Core_and_Builtins/2024-08-05-19-28-12.gh-issue-122697.17MvYl.rst

@@ -0,0 +1,2 @@
+Fixed memory leaks at interpreter shutdown in the free-threaded build, and
+also reporting of leaked memory blocks via :option:`-X showrefcount <-X>`.

Objects/obmalloc.c

@@ -1109,9 +1109,12 @@ free_delayed(uintptr_t ptr)
 #ifndef Py_GIL_DISABLED
     free_work_item(ptr);
 #else
-    if (_PyRuntime.stoptheworld.world_stopped) {
-        // Free immediately if the world is stopped, including during
-        // interpreter shutdown.
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    if (_PyInterpreterState_GetFinalizing(interp) != NULL ||
+        interp->stoptheworld.world_stopped)
+    {
+        // Free immediately during interpreter shutdown or if the world is
+        // stopped.
         free_work_item(ptr);
         return;
     }
@@ -1474,6 +1477,8 @@ _PyInterpreterState_FinalizeAllocatedBlocks(PyInterpreterState *interp)
 {
 #ifdef WITH_MIMALLOC
     if (_PyMem_MimallocEnabled()) {
+        Py_ssize_t leaked = _PyInterpreterState_GetAllocatedBlocks(interp);
+        interp->runtime->obmalloc.interpreter_leaks += leaked;
         return;
     }
 #endif

Python/gc_free_threading.c

@@ -55,6 +55,7 @@ struct collection_state {
     struct visitor_args base;
     PyInterpreterState *interp;
     GCState *gcstate;
+    _PyGC_Reason reason;
     Py_ssize_t collected;
     Py_ssize_t uncollectable;
     Py_ssize_t long_lived_total;
@@ -572,6 +573,16 @@ scan_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
             worklist_push(&state->unreachable, op);
         }
     }
+    else if (state->reason == _Py_GC_REASON_SHUTDOWN &&
+             _PyObject_HasDeferredRefcount(op))
+    {
+        // Disable deferred refcounting for reachable objects as well during
+        // interpreter shutdown. This ensures that these objects are collected
+        // immediately when their last reference is removed.
+        disable_deferred_refcounting(op);
+        merge_refcount(op, 0);
+        state->long_lived_total++;
+    }
     else {
         // object is reachable, restore `ob_tid`; we're done with these objects
         gc_restore_tid(op);
@@ -1228,6 +1239,7 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     struct collection_state state = {
         .interp = interp,
         .gcstate = gcstate,
+        .reason = reason,
     };
 
     gc_collect_internal(interp, &state, generation);

Python/pylifecycle.c

@@ -28,6 +28,7 @@
 #include "pycore_sliceobject.h"   // _PySlice_Fini()
 #include "pycore_sysmodule.h"     // _PySys_ClearAuditHooks()
 #include "pycore_traceback.h"     // _Py_DumpTracebackThreads()
+#include "pycore_typeid.h"        // _PyType_FinalizeIdPool()
 #include "pycore_typeobject.h"    // _PyTypes_InitTypes()
 #include "pycore_typevarobject.h" // _Py_clear_generic_types()
 #include "pycore_unicodeobject.h" // _PyUnicode_InitTypes()
@@ -1832,6 +1833,9 @@ finalize_interp_types(PyInterpreterState *interp)
     _PyTypes_FiniTypes(interp);
 
     _PyTypes_Fini(interp);
+#ifdef Py_GIL_DISABLED
+    _PyType_FinalizeIdPool(interp);
+#endif
 
     _PyCode_Fini(interp);
 

Python/pystate.c

@@ -20,7 +20,7 @@
 #include "pycore_runtime_init.h"  // _PyRuntimeState_INIT
 #include "pycore_sysmodule.h"     // _PySys_Audit()
 #include "pycore_obmalloc.h"      // _PyMem_obmalloc_state_on_heap()
-#include "pycore_typeid.h"        // _PyType_FinalizeIdPool
+#include "pycore_typeid.h"        // _PyType_FinalizeThreadLocalRefcounts()
 
 /* --------------------------------------------------------------------------
 CAUTION