Etc is not Ractor-safe currently

ext/etc/etc.c

@@ -1163,14 +1163,27 @@ Init_etc(void)
 {
     VALUE mEtc;
 
-#ifdef HAVE_RB_EXT_RACTOR_SAFE
-    RB_EXT_RACTOR_SAFE(true);
-#endif
     mEtc = rb_define_module("Etc");
     /* The version */
     rb_define_const(mEtc, "VERSION", rb_str_new_cstr(RUBY_ETC_VERSION));
     init_constants(mEtc);
 
+    /* Ractor-safe methods */
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
+    RB_EXT_RACTOR_SAFE(true);
+#endif
+    rb_define_module_function(mEtc, "sysconfdir", etc_sysconfdir, 0);
+    rb_define_module_function(mEtc, "systmpdir", etc_systmpdir, 0);
+    rb_define_module_function(mEtc, "uname", etc_uname, 0);
+    rb_define_module_function(mEtc, "sysconf", etc_sysconf, 1);
+    rb_define_module_function(mEtc, "confstr", etc_confstr, 1);
+    rb_define_method(rb_cIO, "pathconf", io_pathconf, 1);
+    rb_define_module_function(mEtc, "nprocessors", etc_nprocessors, 0);
+
+    /* Non-Ractor-safe methods, see https://bugs.ruby-lang.org/issues/21115 */
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
+    RB_EXT_RACTOR_SAFE(false);
+#endif
     rb_define_module_function(mEtc, "getlogin", etc_getlogin, 0);
 
     rb_define_module_function(mEtc, "getpwuid", etc_getpwuid, -1);
@@ -1186,13 +1199,6 @@ Init_etc(void)
     rb_define_module_function(mEtc, "setgrent", etc_setgrent, 0);
     rb_define_module_function(mEtc, "endgrent", etc_endgrent, 0);
     rb_define_module_function(mEtc, "getgrent", etc_getgrent, 0);
-    rb_define_module_function(mEtc, "sysconfdir", etc_sysconfdir, 0);
-    rb_define_module_function(mEtc, "systmpdir", etc_systmpdir, 0);
-    rb_define_module_function(mEtc, "uname", etc_uname, 0);
-    rb_define_module_function(mEtc, "sysconf", etc_sysconf, 1);
-    rb_define_module_function(mEtc, "confstr", etc_confstr, 1);
-    rb_define_method(rb_cIO, "pathconf", io_pathconf, 1);
-    rb_define_module_function(mEtc, "nprocessors", etc_nprocessors, 0);
 
     sPasswd =  rb_struct_define_under(mEtc, "Passwd",
 				      "name",

test/etc/test_etc.rb

@@ -173,7 +173,49 @@ def test_sysconfdir
     assert_operator(File, :absolute_path?, Etc.sysconfdir)
   end if File.method_defined?(:absolute_path?)
 
-  def test_ractor
+  # All Ractor-safe methods should be tested here
+  def test_ractor_parallel
+    assert_ractor(<<~RUBY, require: 'etc')
+      20.times.map do
+        Ractor.new do
+          1000.times do
+            raise unless String === Etc.sysconfdir
+            raise unless String === Etc.systmpdir
+            raise unless Hash === Etc.uname
+            if defined?(Etc::SC_CLK_TCK)
+              raise unless Integer === Etc.sysconf(Etc::SC_CLK_TCK)
+            end
+            if defined?(Etc::CS_PATH)
+              raise unless String === Etc.confstr(Etc::CS_PATH)
+            end
+            if defined?(Etc::PC_PIPE_BUF)
+              IO.pipe { |r, w|
+                val = w.pathconf(Etc::PC_PIPE_BUF)
+                raise unless val.nil? || val.kind_of?(Integer)
+              }
+            end
+            raise unless Integer === Etc.nprocessors
+          end
+        end
+      end.each(&:take)
+    RUBY
+  end
+
+  def test_ractor_unsafe
+    assert_ractor(<<~RUBY, require: 'etc')
+      r = Ractor.new do
+        begin
+          Etc.passwd
+        rescue => e
+          e.class
+        end
+      end.take
+      assert_equal Ractor::UnsafeError, r
+    RUBY
+  end
+
+  def test_ractor_passwd
+    omit("https://bugs.ruby-lang.org/issues/21115")
     return unless Etc.passwd # => skip test if no platform support
     Etc.endpwent
 
@@ -197,4 +239,18 @@ def test_ractor
       assert_equal(name2, name)
     RUBY
   end
+
+  def test_ractor_getgrgid
+    omit("https://bugs.ruby-lang.org/issues/21115")
+
+    assert_ractor(<<~RUBY, require: 'etc')
+      20.times.map do
+        Ractor.new do
+          1000.times do
+            raise unless Etc.getgrgid(Process.gid).gid == Process.gid
+          end
+        end
+      end.each(&:take)
+    RUBY
+  end
 end