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gh-112529: Remove PyGC_Head from object pre-header in free-threaded build (#114564)

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* gh-112529: Remove PyGC_Head from object pre-header in free-threaded build

This avoids allocating space for PyGC_Head in the free-threaded build.
The GC implementation for free-threaded CPython does not use the
PyGC_Head structure.

 * The trashcan mechanism uses the `ob_tid` field instead of `_gc_prev`
   in the free-threaded build.
 * The GDB libpython.py file now determines the offset of the managed
   dict field based on whether the running process is a free-threaded
   build. Those are identified by the `ob_ref_local` field in PyObject.
 * Fixes `_PySys_GetSizeOf()` which incorrectly incorrectly included the
   size of `PyGC_Head` in the size of static `PyTypeObject`.
This commit is contained in:
Sam Gross 2024-02-01 15:29:19 -05:00 • committed by GitHub
parent 500ede0117
commit 587d480203
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GPG key ID: B5690EEEBB952194
9 changed files with 86 additions and 26 deletions
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13
Objects/object.c
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@ -2671,7 +2671,12 @@ _PyTrash_thread_deposit_object(struct _py_trashcan *trash, PyObject *op)
_PyObject_ASSERT(op, _PyObject_IS_GC(op));
_PyObject_ASSERT(op, !_PyObject_GC_IS_TRACKED(op));
_PyObject_ASSERT(op, Py_REFCNT(op) == 0);
#ifdef Py_GIL_DISABLED
_PyObject_ASSERT(op, op->ob_tid == 0);
op->ob_tid = (uintptr_t)trash->delete_later;
#else
_PyGCHead_SET_PREV(_Py_AS_GC(op), (PyGC_Head*)trash->delete_later);
#endif
trash->delete_later = op;
}
@ -2697,8 +2702,12 @@ _PyTrash_thread_destroy_chain(struct _py_trashcan *trash)
PyObject *op = trash->delete_later;
destructor dealloc = Py_TYPE(op)->tp_dealloc;
trash->delete_later =
(PyObject*) _PyGCHead_PREV(_Py_AS_GC(op));
#ifdef Py_GIL_DISABLED
trash->delete_later = (PyObject*) op->ob_tid;
op->ob_tid = 0;
#else
trash->delete_later = (PyObject*) _PyGCHead_PREV(_Py_AS_GC(op));
#endif
/* Call the deallocator directly. This used to try to
* fool Py_DECREF into calling it indirectly, but