initialize method tables before any GC chance

Author: tagomoris

class.c

@@ -1183,7 +1183,7 @@ static void
 class_initialize_method_table(VALUE c)
 {
     // initialize the prime classext m_tbl
-    RCLASS_SET_M_TBL(c, rb_id_table_create(0));
+    RCLASS_SET_M_TBL_EVEN_WHEN_PROMOTED(c, rb_id_table_create(0));
 }
 
 static void
@@ -1206,9 +1206,12 @@ rb_class_boot(VALUE super)
 {
     VALUE klass = class_alloc(T_CLASS, rb_cClass);
 
-    class_associate_super(klass, super, true);
+    // initialize method table prior to class_associate_super()
+    // because class_associate_super() may cause GC and promote klass
     class_initialize_method_table(klass);
 
+    class_associate_super(klass, super, true);
+
     return (VALUE)klass;
 }
 
@@ -1492,7 +1495,9 @@ rb_mod_init_copy(VALUE clone, VALUE orig)
         struct clone_method_arg arg;
         arg.old_klass = orig;
         arg.new_klass = clone;
-        class_initialize_method_table(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));
         rb_id_table_foreach(RCLASS_M_TBL(orig), clone_method_i, &arg);
     }
 
@@ -1609,6 +1614,9 @@ rb_singleton_class_clone_and_attach(VALUE obj, VALUE attach)
             RBASIC_SET_CLASS(clone, klass_metaclass_clone);
         }
 
+        // initialize method table before any GC chance
+        class_initialize_method_table(clone);
+
         rb_class_set_super(clone, RCLASS_SUPER(klass));
         rb_iv_tbl_copy(clone, klass);
         if (RCLASS_CONST_TBL(klass)) {
@@ -1622,7 +1630,6 @@ rb_singleton_class_clone_and_attach(VALUE obj, VALUE attach)
         if (!UNDEF_P(attach)) {
             rb_singleton_class_attached(clone, attach);
         }
-        class_initialize_method_table(clone);
         {
             struct clone_method_arg arg;
             arg.old_klass = klass;

internal/class.h

@@ -256,8 +256,8 @@ static inline st_table * RCLASS_WRITABLE_IV_HASH(VALUE obj);
 static inline uint32_t RCLASS_IV_COUNT(VALUE obj);
 static inline void RCLASS_SET_IV_HASH(VALUE obj, const st_table *table);
 static inline void RCLASS_WRITE_IV_HASH(VALUE obj, const st_table *table);
-static inline void RCLASS_SET_M_TBL(VALUE klass, struct rb_id_table *table);
-// TODO: rename RCLASS_WRITE_M_TBL_WORKAROUND to RCLASS_WRITE_M_TBL with write barrier
+// 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_WRITE_CONST_TBL(VALUE klass, struct rb_id_table *table, bool shared);
@@ -562,10 +562,13 @@ RCLASS_IV_COUNT(VALUE obj)
     }
 }
 
+#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
-RCLASS_SET_M_TBL(VALUE klass, struct rb_id_table *table)
+RCLASS_SET_M_TBL_WORKAROUND(VALUE klass, struct rb_id_table *table, bool check_promoted)
 {
-    RUBY_ASSERT(!RB_OBJ_PROMOTED(klass));
+    RUBY_ASSERT(!check_promoted || !RB_OBJ_PROMOTED(klass));
     RCLASSEXT_M_TBL(RCLASS_EXT(klass)) = table;
 }