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Cleanup M_TBL workarounds and comments

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Previously we had an assertion that the method table was only set on
young objects, and a comment stating that was how it needed to be used.
I think that confused the complexity of the write barriers that may be
needed here.

* Setting an empty M_TBL never needs a write barrier
* T_CLASS and T_MODULE should always fire a write barrier to newly added
  methods
* T_ICLASS only needs a write barrier to methods when
  RCLASSEXT_ICLASS_IS_ORIGIN(x) && !RCLASSEXT_ICLASS_ORIGIN_SHARED_MTBL(x)

We shouldn't assume that the object being young is sufficient, because
we also need write barriers for incremental marking and it's unreliable.
This commit is contained in:
John Hawthorn 2025-07-23 12:12:58 -07:00
parent d67eb07f75
commit 9256442615
2 changed files with 7 additions and 25 deletions
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15
class.c
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@ -734,13 +734,13 @@ static void
class_initialize_method_table(VALUE c)
{
// initialize the prime classext m_tbl
RCLASS_SET_M_TBL_EVEN_WHEN_PROMOTED(c, rb_id_table_create(0));
RCLASS_SET_M_TBL(c, rb_id_table_create(0));
}
static void
class_clear_method_table(VALUE c)
{
RCLASS_WRITE_M_TBL_EVEN_WHEN_PROMOTED(c, rb_id_table_create(0));
RCLASS_WRITE_M_TBL(c, rb_id_table_create(0));
}
static VALUE
@ -978,7 +978,7 @@ copy_tables(VALUE clone, VALUE orig)
RCLASS_WRITE_CVC_TBL(clone, rb_cvc_tbl_dup);
}
rb_id_table_free(RCLASS_M_TBL(clone));
RCLASS_WRITE_M_TBL_EVEN_WHEN_PROMOTED(clone, 0);
RCLASS_WRITE_M_TBL(clone, 0);
if (!RB_TYPE_P(clone, T_ICLASS)) {
rb_fields_tbl_copy(clone, orig);
}
@ -1053,9 +1053,7 @@ rb_mod_init_copy(VALUE clone, VALUE orig)
struct clone_method_arg arg;
arg.old_klass = orig;
arg.new_klass = clone;
// TODO: use class_initialize_method_table() instead of RCLASS_SET_M_TBL_*
// after RCLASS_SET_M_TBL is protected by write barrier
RCLASS_SET_M_TBL_EVEN_WHEN_PROMOTED(clone, rb_id_table_create(0));
class_initialize_method_table(clone);
rb_id_table_foreach(RCLASS_M_TBL(orig), clone_method_i, &arg);
}
@ -1081,9 +1079,6 @@ rb_mod_init_copy(VALUE clone, VALUE orig)
rb_bug("non iclass between module/class and origin");
}
clone_p = class_alloc(T_ICLASS, METACLASS_OF(p));
/* We should set the m_tbl right after allocation before anything
* that can trigger GC to avoid clone_p from becoming old and
* needing to fire write barriers. */
RCLASS_SET_M_TBL(clone_p, RCLASS_M_TBL(p));
rb_class_set_super(prev_clone_p, clone_p);
prev_clone_p = clone_p;
@ -1973,7 +1968,7 @@ rb_prepend_module(VALUE klass, VALUE module)
if (klass_had_no_origin && klass_origin_m_tbl == RCLASS_M_TBL(subclass)) {
// backfill an origin iclass to handle refinements and future prepends
rb_id_table_foreach(RCLASS_M_TBL(subclass), clear_module_cache_i, (void *)subclass);
RCLASS_WRITE_M_TBL_EVEN_WHEN_PROMOTED(subclass, klass_m_tbl);
RCLASS_WRITE_M_TBL(subclass, klass_m_tbl);
VALUE origin = rb_include_class_new(klass_origin, RCLASS_SUPER(subclass));
rb_class_set_super(subclass, origin);
RCLASS_SET_INCLUDER(origin, RCLASS_INCLUDER(subclass));