Feature #18919: Ractor: can't share #Method objects

• Status: Assigned
• Assignee: ko1 (Koichi Sasada)
• Target version: -

[chucke (Tiago Cardoso)]

The following is not shareable:

> meth = ::Kernel.method(:BigDecimal)
=> #<Method: Kernel.BigDecimal(*)>
<internal:ractor>:816:in `make_shareable': can not make shareable object for #<Method: Kernel.BigDecimal(*)> (Ractor::Error)

I understand that procs have the issue of accessing outer-scope variables, but does the same apply to methods converted to procs?

[shan (Shannon Skipper)]

This is just an aside, but for what it's worth you can pass the class and method name and reconstitute a Method instance inside a Ractor.

require 'bigdecimal'

meth = Kernel.method(:BigDecimal)

ractor = Ractor.new(meth.owner, meth.name) do |meth_owner, meth_name|
  meth_owner.method(meth_name)
end

ractor.take.call(42)
#=> 0.42e2

[Eregon (Benoit Daloze)]

I don't see a .to_proc call in the description.
Either way, both Method and Proc objects can't be shared, they have mutable state.

For Method/UnboundMethod they could potentially be made immutable and therefore shareable (sounds good to me), but it would be a potentially-breaking change.

[chucke (Tiago Cardoso)]

• Subject changed from Ractor: can't share method-to-proc objects to Ractor: can't share #Method objects

Indeed, I didn't mean "to-proc", Method objects, as per the usage example, is the one I meant.

[ko1 (Koichi Sasada)]

• Assignee set to ko1 (Koichi Sasada)

Now Method object is not shareable, but if the receiver is shareable, we can make it shareable.
Matz asked me to make it shareable, so we can consider the spec.

[hsbt (Hiroshi SHIBATA)]

• Status changed from Open to Assigned

[jeremyevans0 (Jeremy Evans)]

• Tracker changed from Bug to Feature
• Backport deleted (2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN)