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This PR moves us from `Mutex` to `Atomic` for scalar integer values that don't need a full mutex guarding them. On Darwin, we cannot use types from the `Synchronization` module because we need to back-deploy earlier than they are available, so we simulate a subset of the `Atomic` API using a mutex. This is not a performance regression on Darwin since we're already using a mutex there anyway. For this initial PR, I have not attempted to use any atomic orderings other than `.sequentiallyConsistent`. We can revise later on a case-by-case basis.
grynspan
requested review from
briancroom,
harlanhaskins,
jerryjrchen and
stmontgomery
as code owners
grynspan
added
enhancement
jerryjrchen
approved these changes
Mar 2, 2026
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This PR moves us from
MutextoAtomicfor scalar integer values that don't need a full mutex guarding them.On Darwin, we cannot use types from the
Synchronizationmodule because we need to back-deploy earlier than they are available, so we simulate a subset of theAtomicAPI using C atomic intrinsics provided by clang and bubbled up through Stubs.h. Unlike the realAtomictype, we heap-allocate our storage, but we're heap-allocating the current mutex so that isn't a performance regression.I have only implemented the set of functionality we're actually using; adding more functionality isn't hard, but is beyond the scope of this PR. In particular, I have not attempted to implement/use any atomic orderings other than
.sequentiallyConsistent. We can revise orderings later on a case-by-case basis.Checklist: