On Apr 3, 2006, at 3:12 PM, Neil Schemenauer wrote:
> Guido van Rossum <guido at python.org> wrote:
>> This would require a bit "__del__ already called" on an object,
>> but don't we have a whole word of GC-related flags?
>
> No.
Actually there is. Kinda. Currently python's refcounting scheme uses
4 words per object (gc_next, gc_prev, gc_refs, ob_refcnt), and has
one spare word in the padding of PyGC_Head that's just sitting there
wasting memory. So really it's using up 5 words per object, and that
5th word could actually be used for flags...
/* GC information is stored BEFORE the object structure. */
typedef union _gc_head {
struct {
union _gc_head *gc_next;
union _gc_head *gc_prev;
int gc_refs;
} gc;
long double dummy; /* force worst-case alignment */
} PyGC_Head;
#define PyObject_HEAD \
_PyObject_HEAD_EXTRA \
int ob_refcnt; \
struct _typeobject *ob_type;
typedef struct _object {
PyObject_HEAD
} PyObject;
James
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