[bigdecimal] Make bigdecimal Ractor safe

https://github.com/ruby/bigdecimal/commit/93fc392640
https://github.com/ruby/bigdecimal/commit/a90d13c4d0

ext/bigdecimal/bigdecimal.c

@@ -189,11 +189,16 @@ BigDecimal_memsize(const void *ptr)
     return (sizeof(*pv) + pv->MaxPrec * sizeof(BDIGIT));
 }
 
+#ifndef HAVE_RB_EXT_RACTOR_SAFE
+#   undef RUBY_TYPED_FROZEN_SHAREABLE
+#   define RUBY_TYPED_FROZEN_SHAREABLE 0
+#endif
+
 static const rb_data_type_t BigDecimal_data_type = {
     "BigDecimal",
     { 0, BigDecimal_delete, BigDecimal_memsize, },
 #ifdef RUBY_TYPED_FREE_IMMEDIATELY
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_FROZEN_SHAREABLE
 #endif
 };
 
@@ -3351,6 +3356,9 @@ get_vp_value:
 void
 Init_bigdecimal(void)
 {
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
+    rb_ext_ractor_safe(true);
+#endif
     VALUE arg;
 
     id_BigDecimal_exception_mode = rb_intern_const("BigDecimal.exception_mode");
@@ -3617,6 +3625,9 @@ static void VpFormatSt(char *psz, size_t fFmt);
 static int VpRdup(Real *m, size_t ind_m);
 
 #ifdef BIGDECIMAL_DEBUG
+# ifdef HAVE_RB_EXT_RACTOR_SAFE
+#  error Need to make rewiting gnAlloc atomic
+# endif
 static int gnAlloc = 0; /* Memory allocation counter */
 #endif /* BIGDECIMAL_DEBUG */
 

test/bigdecimal/test_ractor.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+require_relative "testbase"
+
+class TestBigDecimalRactor < Test::Unit::TestCase
+  include TestBigDecimalBase
+
+  def setup
+    super
+    skip unless defined? Ractor
+  end
+
+  def test_ractor_shareable
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      $VERBOSE = nil
+      require "bigdecimal"
+      r = Ractor.new BigDecimal(Math::PI, Float::DIG+1) do |pi|
+        BigDecimal('2.0')*pi
+      end
+      assert_equal(2*Math::PI, r.take)
+    end;
+  end
+end