Avoid holding MergeStorage lock across continuation registration - #444
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thliu21 wants to merge 2 commits into
Open
Avoid holding MergeStorage lock across continuation registration#444thliu21 wants to merge 2 commits into
thliu21 wants to merge 2 commits into
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FranzBusch
reviewed
Jul 22, 2026
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We really should remove all the manual lock/unlock calls now and only use withLock
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I think we should also split this function up, as we did for AsyncStream and MPSC Channel.
NotTheNHK
reviewed
Jul 22, 2026
| // The continuation is registered after `next()` releases the lock. While | ||
| // it was unlocked, an upstream may have produced an element or finished. | ||
| if let element = buffer.popFirst() { | ||
| state = .merging( |
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I think it would be a good idea to eventually refactor this into a single type. We can do that in a separate PR.
thliu21
marked this pull request as ready for review
July 22, 2026 15:48
FranzBusch
approved these changes
Jul 23, 2026
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Summary
MergeStoragedownstream continuations after releasing the thread-affine lockRoot cause
MergeStorage.next()previously held its lock while enteringwithUnsafeThrowingContinuation. Swift 6.0–6.3.3 could re-enqueue before that closure executed, allowing a thread-affine lock to be unlocked from a different thread. The state machine now owns the race window explicitly, so continuation registration is protected by a short lock acquisition instead.Validation
swift test --filter TestMerge— 32 tests passedswift test— 362 tests passedgit diff --checkFixes #430.