close_incoming by antoher ractor means there is no other messages
will be sent to the ractor, so Ractor.receive will block forever,
and it should raise and stop.
close_outgoing by antoher ractor means, ... I don't have good idea
to use it. It can be a private method.
Ractor#close calls both, but it does not make sense to call
different purpose methods, so I remove it.
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.
This commit introduces Ractor mechanism to run Ruby program in
parallel. See doc/ractor.md for more details about Ractor.
See ticket [Feature #17100] to see the implementation details
and discussions.
[Feature #17100]
This commit does not complete the implementation. You can find
many bugs on using Ractor. Also the specification will be changed
so that this feature is experimental. You will see a warning when
you make the first Ractor with `Ractor.new`.
I hope this feature can help programmers from thread-safety issues.
