Issue #8259 has been updated by Vit Z. Eric Wong wrote: > Right. There's no way I will ever advocate a memory barrier of any > kind by default for reads or in-place updates. > > Unfortunately, changing capacity of an array or hash is tricky and > probably requires barriers for most or all cases (unless escape analysis > can elide barriers, but that's pie-in-the-sky territory). My thesis and objection to adding "atomic" methods to `Array` or `Hash` is that it would necessarily entail making them thread-safe as a whole. However making them thread-safe on concurrent Ruby VMs is costly and carries a performance penalty even for a single threaded usage. It will also be impossible to undo (once Ruby declares `Hash` to be safe to use concurrently, there is no going back on this). I am all for addition of `ConcurrentHash` or `Concurrent::Array` (these new data structures would have `cas` and `swap` methods), but for performance reasons plain old `Hash` and `Array` should be kept completely un-thread-safe. ---------------------------------------- Feature #8259: Atomic attributes accessors https://bugs.ruby-lang.org/issues/8259#change-47156 * Author: Yura Sokolov * Status: Open * Priority: Normal * Assignee: * Category: * Target version: Ruby 2.1.0 ---------------------------------------- =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: 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 -- https://bugs.ruby-lang.org/