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Feature #8259

Updated by hsbt (Hiroshi SHIBATA) almost 5 years ago

=begin
Motivated by this gist ((<URL:https://gist.github.com/jstorimer/5298581>)) and atomic gem

I propose Class.attr_atomic which will add methods for atomic swap and CAS:

```ruby


class MyNode
attr_accessor :item
attr_atomic :successor

def initialize(item, successor)
@item = item
@successor = successor
end
end
node = MyNode.new(i, other_node)

# attr_atomic ensures at least #{attr} reader method exists. May be, it should
# be sure it does volatile access.
node.successor

# #{attr}_cas(old_value, new_value) do CAS: atomic compare and swap
if node.successor_cas(other_node, new_node)
print "there were no interleaving with other threads"
end

# #{attr}_swap atomically swaps value and returns old value.
# It ensures that no other thread interleaves getting old value and setting
# new one by cas (or other primitive if exists, like in Java 8)
node.successor_swap(new_node)
```


It will be very simple for MRI cause of GIL, and it will use atomic primitives for
other implementations.

Note: both (({#{attr}_swap})) and (({#{attr}_cas})) should raise an error if instance variable were not explicitly set before.

Example for nonblocking queue: ((<URL:https://gist.github.com/funny-falcon/5370416>))

Something similar should be proposed for Structs. May be override same method as (({Struct.attr_atomic}))

Open question for reader:
should (({attr_atomic :my_attr})) ensure that #my_attr reader method exists?
Should it guarantee that (({#my_attr})) provides 'volatile' access?
May be, (({attr_reader :my_attr})) already ought to provide 'volatile' semantic?
May be, semantic of (({@my_attr})) should have volatile semantic (i doubt for that)?
=end

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