SE-0410: Atomics

[taylorswift]

@wadetregaskis

Before I read to that part of the proposal, I actually spent a bunch of time trying to figure out how to derive this from the earlier primitives (e.g. Atomic<Unmanaged<T>>) but ran into challenges exactly as the proposal mentions regarding reference counting. It makes me wonder whether the inclusion of Unmanaged (perhaps among others?) in the atomic world should be made private, given how difficult it is to use correctly.

you might be interested in many of the replies to this thread:

Use swift-atomics to track a “largest seen value”?

this is sort of a continuation from How to use swift-atomics to expose non-isolated state of an actor? is there a good algorithm for updating an atomic value only if the new value is larger than the old value? for example, i would like let currentTime:UnsafeAtomic<UInt64> to only update the time if it is larger than the current time, so that the time increases monotonically. one idea i had was to use exchange(_:ordering:) and roll back the change if the old value ended up being greater than…