Use a monotonically increasing number for object_id

This changes object_id from being based on the objects location in
memory (or a nearby memory location in the case of a conflict) to be
based on an always increasing number.

This number is a Ruby Integer which allows it to overflow the size of a
pointer without issue (very unlikely to happen in real programs
especially on 64-bit, but a nice guarantee).

This changes obj_to_id_tbl and id_to_obj_tbl to both be maps of Ruby
objects to Ruby objects (previously they were Ruby object to C integer)
which simplifies updating them after compaction as we can run them
through gc_update_table_refs.

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index 1511ea3011..f42e098863 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -461,4 +461,12 @@ class TestGc < Test::Unit::TestCase
     skip "finalizers did not get run" if @result.empty?
     assert_equal([:c1, :c2], @result)
   end
+
+  def test_object_ids_never_repeat
+    GC.start
+    a = 1000.times.map { Object.new.object_id }
+    GC.start
+    b = 1000.times.map { Object.new.object_id }
+    assert_empty(a & b)
+  end
 end