Move object_id in attributes
#13159
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Move object_id in attributes
#13159
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casperisfine
commented
Apr 24, 2025
gc/default/default.c
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| } | ||
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| if (rb_shape_has_object_id(shape)) { | ||
| // We could avoid locking if the object isn't shareable |
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For T_MODULE and T_CLASS it might be worth finding 8B in rb_classext_t so we can do some atomic CAS and find_or_create the object_id with no actual locking.
But if we need to also set the FL_SEEN_OBJ_ID flag, it might be more tricky than that?
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casperisfine
commented
Apr 29, 2025
gc.c
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| void | ||
| rb_gc_obj_free_vm_weak_references(VALUE obj) | ||
| { | ||
| if (FL_TEST_RAW(obj, FL_SEEN_OBJ_ID)) { |
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FL_SEEN_OBJ_ID isn't very useful anymore, except for SHAPE_TOO_COMPLEX, but we could improve that too.
If we always check the shape flags, we could reclaim that flag.
Also more broadly, shape_id_t is 32bit on 64bit systems, which is way more than we need. If needing to lookup the shape to know if it has an object_id (or is frozen) we could actually pack these tags in the most significant bits of the shape_id.
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This opens the door to store more informations in shapes, such as the `object_id` or object address in case it has been observed and the object has to be moved.
And get rid of the `obj_to_id_tbl` It's no longer needed, the `object_id` is now stored inline in the object. We still need the inverse table in case `_id2ref` is invoked, but we lazily build it by walking the heap if that happens.
We can't do unsychronized reads for shareable objects, which include all modules and classes.
Since we assume most programs don't ever build the id2obj table, we can just implement it as a simple TypedData object.
Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>
Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>
Ivars no longer are the only thing stored inline via shapes, so keeping `iv_index` would be confusing.
Right now everything assume only one shape is too_complex. e.g. `shape_id == OBJ_TOO_COMPLEX_SHAPE_ID`. In the near future I'd like to have more than one complex shape, e.g. `frozen & too_complex`, `have_id & too_complex`.
You still cannot transition from TOO_COMPLEX into an IVAR shape, however you now can transitiont o FROZEN or OBJ_ID. This allows to store in the shape that we're froen or have an object_id, allowing to free object flags.
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And get rid of the
obj_to_id_tblIt's no longer needed, the
object_idis now stored inlinein the object.
We still need the inverse table in case
_id2refis invoked, butwe lazily build it by walking the heap if that happens.