Add Synchronized guarded-value locks with RAII-style holder handles - #1704
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🦋 Changeset detectedLatest commit: 07dd867 The changes in this PR will be included in the next version bump. This PR includes changesets to release 2 packages
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Lock returns the guarded value and a Holder; Unlock is a method on the handle, so releases match acquisitions exactly (including cross- goroutine handoff). Exclusive-only: with at most one holder, the guarded mutex synchronizes all bookkeeping — no atomics except the waiter count — and the by-value Holder never escapes: 5.5ns per Lock/Unlock with zero allocations (tracked Mutex 6.3ns, native 4.0ns). ScanTrackedLocks reports these locks alongside the existing trackers. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Motivation
Stacked on #1701. Review there surfaced the root problem with any drop-in
sync.Mutextracker: release is keyed by goroutine id, so cross-goroutine unlocks need heuristics (arbitrary eviction — the same policy go-deadlock uses) and holder tracking needs a slot cap.Synchronized[T]is the design that eliminates the class:Lockreturns the guarded value plus aHolderhandle andUnlockis a method on the handle.Design
Exclusive mutex only — and that exclusivity is what keeps it simple: with at most one holder, all holder bookkeeping (gid, acquisition time, optional acquisition stack) is written under the guarded mutex itself, so nothing needs atomics except the waiter count (maintained outside the lock). No holder list. The
Holderis returned by value and never escapes — zero allocations.Synchronized[T]guards its value:v, h := s.Lock()…h.Unlock(). The zero value works.ScanTrackedLocksreports these locks alongside the existing tracker (holder gid,HeldSince, waiter count, acquisition stack whenToggleLockTrackerStackTracesis on), soPopulateHolderStacksand downstream stuck-lock logging work unchanged. The scanner reads bookkeeping without taking the lock, tolerating racy reads exactly like the existinglockTrackerscan.Numbers (Apple M5 Pro, uncontended Lock/Unlock pair)
Intent
Successor primitive for hot, incident-prone exclusive locks (room locks, dispatcher pools) to migrate to incrementally; #1701 remains the drop-in improvement for the existing
utils.Mutex/RWMutexfleet (RW locks are few and keep the slot-based tracking).🤖 Generated with Claude Code