Ractor.make_shareable(obj)

Introduce new method Ractor.make_shareable(obj) which tries to make
obj shareable object. Protocol is here.

(1) If obj is shareable, it is shareable.
(2) If obj is not a shareable object and if obj can be shareable
    object if it is frozen, then freeze obj. If obj has reachable
    objects (rs), do rs.each{|o| Ractor.make_shareable(o)}
    recursively (recursion is not Ruby-level, but C-level).
(3) Otherwise, raise Ractor::Error. Now T_DATA is not a shareable
    object even if the object is frozen.

If the method finished without error, given obj is marked as
a sharable object.

To allow makng a shareable frozen T_DATA object, then set
`RUBY_TYPED_FROZEN_SHAREABLE` as type->flags. On default,
this flag is not set. It means user defined T_DATA objects are
not allowed to become shareable objects when it is frozen.

You can make any object  shareable by setting FL_SHAREABLE flag,
so if you know that the T_DATA object is shareable (== thread-safe),
set this flag, at creation time for example. `Ractor` object is one
example, which is not a frozen, but a shareable object.

1 files changed, 6 insertions, 0 deletions

diff --git a/ractor.rb b/ractor.rb
index c825fbe0da..936310d645 100644
--- a/ractor.rb
+++ b/ractor.rb
@@ -173,4 +173,10 @@ class Ractor
       rb_ractor_shareable_p(obj) ? Qtrue : Qfalse;
     }
   end
+
+  def self.make_shareable obj
+    __builtin_cexpr! %q{
+      rb_ractor_make_shareable(obj);
+    }
+  end
 end