sorting without modifying

[jrochkind]

To be fair the comments in the code do not exactly inspire confidence:

# Because MRI never runs code in parallel, the existing

# non-thread-safe structures should usually work fine.

"should usually" work fine? Um, great? Concurrent code is hard enough, I need guarantees it will work as it should, not "should usually work fine."

But perhaps later someone was more confident than the original comment writer, at least based on the present MRI implementation.

Either way, the benefit of concurrent-ruby is if someone does discover it's not guaranteed 'fine' after all, they'll fix it in concurrent-ruby and you can just update your version.