Migrate atomics to Synchronization.Atomic, drop ToolsProtocolsCAtomics#51
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rintaro merged 2 commits intoMay 27, 2026
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ahoppen
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Very nice. We should also be able to get rid of ThreadSafeBox in favor of Mutex.
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Replace the AtomicBool/UInt8/UInt32/Int32 wrapper classes (backed by a small C atomics shim) with Synchronization.Atomic<T>. All sites use .sequentiallyConsistent ordering to match the prior shim's behavior; relaxing per-site is left as a follow-up. The ToolsProtocolsCAtomics target is removed from Package.swift and CMake.
The previous .sequentiallyConsistent ordering on every atomic forced unnecessary barriers (notably dmb ish on ARM). Replace with the minimum ordering each operation actually needs: - ID counters (request/notification/signpost) → .relaxed. Operations only need uniqueness; ordering relative to other memory carries no information. - LoggingScope's "fault logged" once-flag → .relaxed. No associated state rides on the flag. - RequestAndReply.replied → .acquiring on load, .acquiringAndReleasing on exchange. ARC's refcount synchronization in deinit would make .relaxed functionally correct, but acquire/release expresses the operation's intent without leaning on that side-channel.
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hamishknight
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Replace the
AtomicBool/UInt8/UInt32/Int32wrapper classes (backed by a small C atomics shim) withSynchronization.Atomic<T>. TheToolsProtocolsCAtomicstarget is removed from Package.swift and CMake.Also relax atomic memory orderings to
.relaxed. Every atomic in this package is either a unique-ID counter or a "once" flag whose result no other memory reads ride on. None of them synchronize with adjacent non-atomic state, so.relaxedis sufficient and avoids theSEQ_CSTbarriers.