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, 2 insertions, 0 deletions

diff --git a/include/ruby/internal/core/rtypeddata.h b/include/ruby/internal/core/rtypeddata.h
index 3ffe07ec5e..c038e6f2b8 100644
--- a/include/ruby/internal/core/rtypeddata.h
+++ b/include/ruby/internal/core/rtypeddata.h
@@ -52,6 +52,7 @@
 #define RTYPEDDATA_P                 RTYPEDDATA_P
 #define RTYPEDDATA_TYPE              RTYPEDDATA_TYPE
 #define RUBY_TYPED_FREE_IMMEDIATELY  RUBY_TYPED_FREE_IMMEDIATELY
+#define RUBY_TYPED_FROZEN_SHAREABLE  RUBY_TYPED_FROZEN_SHAREABLE
 #define RUBY_TYPED_WB_PROTECTED      RUBY_TYPED_WB_PROTECTED
 #define RUBY_TYPED_PROMOTED1         RUBY_TYPED_PROMOTED1
 /** @endcond */
@@ -59,6 +60,7 @@
 /* bits for rb_data_type_struct::flags */
 enum rbimpl_typeddata_flags {
     RUBY_TYPED_FREE_IMMEDIATELY = 1,
+    RUBY_TYPED_FROZEN_SHAREABLE = RUBY_FL_SHAREABLE,
     RUBY_TYPED_WB_PROTECTED     = RUBY_FL_WB_PROTECTED, /* THIS FLAG DEPENDS ON Ruby version */
     RUBY_TYPED_PROMOTED1        = RUBY_FL_PROMOTED1     /* THIS FLAG DEPENDS ON Ruby version */
 };