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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
View file

@ -734,13 +734,13 @@ static void
class_initialize_method_table(VALUE c) class_initialize_method_table(VALUE c)
{ {
// initialize the prime classext m_tbl // 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 static void
class_clear_method_table(VALUE c) 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 static VALUE
@ -978,7 +978,7 @@ copy_tables(VALUE clone, VALUE orig)
RCLASS_WRITE_CVC_TBL(clone, rb_cvc_tbl_dup); RCLASS_WRITE_CVC_TBL(clone, rb_cvc_tbl_dup);
} }
rb_id_table_free(RCLASS_M_TBL(clone)); 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)) { if (!RB_TYPE_P(clone, T_ICLASS)) {
rb_fields_tbl_copy(clone, orig); rb_fields_tbl_copy(clone, orig);
} }
@ -1053,9 +1053,7 @@ rb_mod_init_copy(VALUE clone, VALUE orig)
struct clone_method_arg arg; struct clone_method_arg arg;
arg.old_klass = orig; arg.old_klass = orig;
arg.new_klass = clone; arg.new_klass = clone;
// TODO: use class_initialize_method_table() instead of RCLASS_SET_M_TBL_* class_initialize_method_table(clone);
// after RCLASS_SET_M_TBL is protected by write barrier
RCLASS_SET_M_TBL_EVEN_WHEN_PROMOTED(clone, rb_id_table_create(0));
rb_id_table_foreach(RCLASS_M_TBL(orig), clone_method_i, &arg); 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"); rb_bug("non iclass between module/class and origin");
} }
clone_p = class_alloc(T_ICLASS, METACLASS_OF(p)); 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)); RCLASS_SET_M_TBL(clone_p, RCLASS_M_TBL(p));
rb_class_set_super(prev_clone_p, clone_p); rb_class_set_super(prev_clone_p, clone_p);
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)) { if (klass_had_no_origin && klass_origin_m_tbl == RCLASS_M_TBL(subclass)) {
// backfill an origin iclass to handle refinements and future prepends // backfill an origin iclass to handle refinements and future prepends
rb_id_table_foreach(RCLASS_M_TBL(subclass), clear_module_cache_i, (void *)subclass); 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)); VALUE origin = rb_include_class_new(klass_origin, RCLASS_SUPER(subclass));
rb_class_set_super(subclass, origin); rb_class_set_super(subclass, origin);
RCLASS_SET_INCLUDER(origin, RCLASS_INCLUDER(subclass)); RCLASS_SET_INCLUDER(origin, RCLASS_INCLUDER(subclass));

17
internal/class.h
View file

@ -259,9 +259,6 @@ static inline void RCLASSEXT_SET_INCLUDER(rb_classext_t *ext, VALUE klass, VALUE
static inline void RCLASS_SET_SUPER(VALUE klass, VALUE super); static inline void RCLASS_SET_SUPER(VALUE klass, VALUE super);
static inline void RCLASS_WRITE_SUPER(VALUE klass, VALUE super); static inline void RCLASS_WRITE_SUPER(VALUE klass, VALUE super);
// TODO: rename RCLASS_SET_M_TBL_WORKAROUND (and _WRITE_) to RCLASS_SET_M_TBL with write barrier
static inline void RCLASS_SET_M_TBL_WORKAROUND(VALUE klass, struct rb_id_table *table, bool check_promoted);
static inline void RCLASS_WRITE_M_TBL_WORKAROUND(VALUE klass, struct rb_id_table *table, bool check_promoted);
static inline void RCLASS_SET_CONST_TBL(VALUE klass, struct rb_id_table *table, bool shared); static inline void RCLASS_SET_CONST_TBL(VALUE klass, struct rb_id_table *table, bool shared);
static inline void RCLASS_WRITE_CONST_TBL(VALUE klass, struct rb_id_table *table, bool shared); static inline void RCLASS_WRITE_CONST_TBL(VALUE klass, struct rb_id_table *table, bool shared);
static inline void RCLASS_WRITE_CALLABLE_M_TBL(VALUE klass, struct rb_id_table *table); static inline void RCLASS_WRITE_CALLABLE_M_TBL(VALUE klass, struct rb_id_table *table);
@ -594,25 +591,15 @@ RCLASS_FIELDS_COUNT(VALUE obj)
return 0; return 0;
} }
#define RCLASS_SET_M_TBL_EVEN_WHEN_PROMOTED(klass, table) RCLASS_SET_M_TBL_WORKAROUND(klass, table, false)
#define RCLASS_SET_M_TBL(klass, table) RCLASS_SET_M_TBL_WORKAROUND(klass, table, true)
static inline void static inline void
RCLASS_SET_M_TBL_WORKAROUND(VALUE klass, struct rb_id_table *table, bool check_promoted) RCLASS_SET_M_TBL(VALUE klass, struct rb_id_table *table)
{ {
RUBY_ASSERT(!check_promoted || !RB_OBJ_PROMOTED(klass));
RCLASSEXT_M_TBL(RCLASS_EXT_PRIME(klass)) = table; RCLASSEXT_M_TBL(RCLASS_EXT_PRIME(klass)) = table;
} }
#define RCLASS_WRITE_M_TBL_EVEN_WHEN_PROMOTED(klass, table) RCLASS_WRITE_M_TBL_WORKAROUND(klass, table, false)
#define RCLASS_WRITE_M_TBL(klass, table) RCLASS_WRITE_M_TBL_WORKAROUND(klass, table, true)
static inline void static inline void
RCLASS_WRITE_M_TBL_WORKAROUND(VALUE klass, struct rb_id_table *table, bool check_promoted) RCLASS_WRITE_M_TBL(VALUE klass, struct rb_id_table *table)
{ {
RUBY_ASSERT(!check_promoted || !RB_OBJ_PROMOTED(klass));
// TODO: add write barrier here to guard assigning m_tbl
// see commit 28a6e4ea9d9379a654a8f7c4b37fa33aa3ccd0b7
RCLASSEXT_M_TBL(RCLASS_EXT_WRITABLE(klass)) = table; RCLASSEXT_M_TBL(RCLASS_EXT_WRITABLE(klass)) = table;
} }