Friday, October 2, 2020

Introducing Swift Atomics

Karoy Lorentey (Hacker News):

I’m delighted to announce Swift Atomics, a new open source package that enables direct use of low-level atomic operations in Swift code. The goal of this library is to enable intrepid systems programmers to start building synchronization constructs (such as concurrent data structures) directly in Swift.


This is enabled by SE-0282, a recently accepted Swift Evolution proposal that explicitly adopted a C/C++-style memory model for Swift, and (informally) described how regular Swift code interoperates with atomic operations. In fact, most APIs in this new package come from previous incarnations of the SE-0282 proposal: they were originally developed by an extremely productive collaborative effort on the Evolution forum.


Atomic access is implemented in terms of dedicated atomic storage representations that are kept distinct from the corresponding regular (non-atomic) type. (E.g., the actual integer value underlying the counter above isn’t directly accessible.)


All atomic operations exposed by this package are guaranteed to have lock-free implementations. Lock-freedom means that the atomic operations are non-blocking – they don’t ever need to wait on the progress of some other thread to complete their own task.


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