allow to access ivars of classes/modules

if an ivar of a class/module refer to a shareable object, this ivar
can be read from non-main Ractors.

benchmark/vm_ivar_of_class.yml

@@ -0,0 +1,12 @@
+prelude: |
+  class C
+    @a = 1
+    def self.a
+      _a = @a; _a = @a; _a = @a; _a = @a; _a = @a;
+      _a = @a; _a = @a; _a = @a; _a = @a; _a = @a;
+    end
+  end
+benchmark:
+  vm_ivar_of_class: |
+    a = C.a
+loop_count: 30000000

bootstraptest/test_ractor.rb

@@ -928,7 +928,7 @@ assert_equal 'ArgumentError', %q{
 }
 
 # ivar in shareable-objects are not allowed to access from non-main Ractor
-assert_equal 'can not access instance variables of classes/modules from non-main Ractors', %q{
+assert_equal "can not get unshareable values from instance variables of classes/modules from non-main Ractors", %q{
   class C
     @iv = 'str'
   end
@@ -1022,6 +1022,53 @@ assert_equal '11', %q{
   }.join
 }
 
+# and instance variables of classes/modules are accessible if they refer shareable objects
+assert_equal '333', %q{
+  class C
+    @int = 1
+    @str = '-1000'.dup
+    @fstr = '100'.freeze
+
+    def self.int = @int
+    def self.str = @str
+    def self.fstr = @fstr
+  end
+
+  module M
+    @int = 2
+    @str = '-2000'.dup
+    @fstr = '200'.freeze
+
+    def self.int = @int
+    def self.str = @str
+    def self.fstr = @fstr
+  end
+
+  a = Ractor.new{ C.int }.take
+  b = Ractor.new do
+    C.str.to_i
+  rescue Ractor::IsolationError
+    10
+  end.take
+  c = Ractor.new do
+    C.fstr.to_i
+  end.take
+
+  d = Ractor.new{ M.int }.take
+  e = Ractor.new do
+    M.str.to_i
+  rescue Ractor::IsolationError
+    20
+  end.take
+  f = Ractor.new do
+    M.fstr.to_i
+  end.take
+
+
+  # 1 + 10 + 100 + 2 + 20 + 200
+  a + b + c + d + e + f
+}
+
 # cvar in shareable-objects are not allowed to access from non-main Ractor
 assert_equal 'can not access class variables from non-main Ractors', %q{
   class C

bootstraptest/test_yjit.rb

@@ -2023,14 +2023,14 @@ assert_normal_exit %q{
   foo([1]) rescue nil
 }
 
-# test ractor exception on when getting ivar
+# test ractor exception on when setting ivar
 assert_equal '42',  %q{
   class A
     def self.foo
       _foo = 1
       _bar = 2
       begin
-        @bar
+        @bar = _foo + _bar
       rescue Ractor::IsolationError
         42
       end

variable.c

@@ -908,7 +908,7 @@ IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(ID id)
 {
     if (UNLIKELY(!rb_ractor_main_p())) {
         if (rb_is_instance_id(id)) { // check only normal ivars
-            rb_raise(rb_eRactorIsolationError, "can not access instance variables of classes/modules from non-main Ractors");
+            rb_raise(rb_eRactorIsolationError, "can not set instance variables of classes/modules by non-main Ractors");
         }
     }
 }
@@ -1185,6 +1185,54 @@ gen_ivtbl_count(const struct gen_ivtbl *ivtbl)
     return n;
 }
 
+static int
+lock_st_lookup(st_table *tab, st_data_t key, st_data_t *value)
+{
+    int r;
+    RB_VM_LOCK_ENTER();
+    {
+        r = st_lookup(tab, key, value);
+    }
+    RB_VM_LOCK_LEAVE();
+    return r;
+}
+
+static int
+lock_st_delete(st_table *tab, st_data_t *key, st_data_t *value)
+{
+    int r;
+    RB_VM_LOCK_ENTER();
+    {
+        r = st_delete(tab, key, value);
+    }
+    RB_VM_LOCK_LEAVE();
+    return r;
+}
+
+static int
+lock_st_is_member(st_table *tab, st_data_t key)
+{
+    int r;
+    RB_VM_LOCK_ENTER();
+    {
+        r = st_is_member(tab, key);
+    }
+    RB_VM_LOCK_LEAVE();
+    return r;
+}
+
+static int
+lock_st_insert(st_table *tab, st_data_t key, st_data_t value)
+{
+    int r;
+    RB_VM_LOCK_ENTER();
+    {
+        r = st_insert(tab, key, value);
+    }
+    RB_VM_LOCK_LEAVE();
+    return r;
+}
+
 VALUE
 rb_ivar_lookup(VALUE obj, ID id, VALUE undef)
 {
@@ -1211,10 +1259,15 @@ rb_ivar_lookup(VALUE obj, ID id, VALUE undef)
         {
             st_data_t val;
 
-            IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(id);
             if (RCLASS_IV_TBL(obj) &&
-                st_lookup(RCLASS_IV_TBL(obj), (st_data_t)id, &val)) {
+                lock_st_lookup(RCLASS_IV_TBL(obj), (st_data_t)id, &val)) {
-                return (VALUE)val;
+                if (rb_is_instance_id(id) &&
+                    UNLIKELY(!rb_ractor_main_p()) &&
+                    !rb_ractor_shareable_p(val)) {
+                    rb_raise(rb_eRactorIsolationError,
+                             "can not get unshareable values from instance variables of classes/modules from non-main Ractors");
+                }
+                return val;
             }
             else {
                 break;
@@ -1270,7 +1323,7 @@ rb_ivar_delete(VALUE obj, ID id, VALUE undef)
         IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(id);
 	if (RCLASS_IV_TBL(obj)) {
             st_data_t id_data = (st_data_t)id, val;
-            if (st_delete(RCLASS_IV_TBL(obj), &id_data, &val)) {
+            if (lock_st_delete(RCLASS_IV_TBL(obj), &id_data, &val)) {
                 return (VALUE)val;
             }
         }
@@ -1554,8 +1607,7 @@ rb_ivar_defined(VALUE obj, ID id)
 	break;
       case T_CLASS:
       case T_MODULE:
-        IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(id);
+        if (RCLASS_IV_TBL(obj) && lock_st_is_member(RCLASS_IV_TBL(obj), (st_data_t)id))
-	if (RCLASS_IV_TBL(obj) && st_is_member(RCLASS_IV_TBL(obj), (st_data_t)id))
 	    return Qtrue;
 	break;
       default:
@@ -1747,8 +1799,12 @@ rb_ivar_foreach(VALUE obj, rb_ivar_foreach_callback_func *func, st_data_t arg)
       case T_MODULE:
         IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(0);
 	if (RCLASS_IV_TBL(obj)) {
+            RB_VM_LOCK_ENTER();
+            {
                 st_foreach_safe(RCLASS_IV_TBL(obj), func, arg);
             }
+            RB_VM_LOCK_LEAVE();
+	}
 	break;
       default:
 	if (FL_TEST(obj, FL_EXIVAR)) {
@@ -1909,7 +1965,7 @@ rb_obj_remove_instance_variable(VALUE obj, VALUE name)
       case T_MODULE:
         IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(id);
 	n = id;
-	if (RCLASS_IV_TBL(obj) && st_delete(RCLASS_IV_TBL(obj), &n, &v)) {
+	if (RCLASS_IV_TBL(obj) && lock_st_delete(RCLASS_IV_TBL(obj), &n, &v)) {
 	    return (VALUE)v;
 	}
 	break;
@@ -3708,7 +3764,7 @@ rb_class_ivar_set(VALUE obj, ID key, VALUE value)
     }
 
     st_table *tbl = RCLASS_IV_TBL(obj);
-    int result = st_insert(tbl, (st_data_t)key, (st_data_t)value);
+    int result = lock_st_insert(tbl, (st_data_t)key, (st_data_t)value);
     RB_OBJ_WRITTEN(obj, Qundef, value);
     return result;
 }