thedarkone2 / gmail.com wrote: > Adding "atomic" operations to built in `Array`s, `Hash`es etc. is a very bad idea > because that would force that *all* of the methods on `Array`s and `Hash`es be > concurrency friendly and would result in irreparable performance problems for > truly concurrent Ruby VMs (and this again would put an upper limit on Ruby > performance). I do atomic operations all the time in C on arbitrary addresses. Lazy, non-atomic accesses run without speed penalty if I don't need up-to-date data. The uncommon case of Array/Hash shrinkage would require RCU or similar (epoch-based reclamation). But there's no penalty for reads or in-place modifications other than the cost of the atomic and required memory barriers. Ruby swap/cas (in Ruby) should probably raise on non-existent Array/Hash elements.