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JavaScriptEventLoop: release the isSpinning latch with defer #809

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JavaScriptEventLoop: release the isSpinning latch with defer #809

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11 changes: 9 additions & 2 deletions Sources/JavaScriptEventLoop/JobQueue.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,15 @@ extension JavaScriptEventLoop {

func runAllJobs() {
assert(queueState.isSpinning)
// `defer`, so the latch is released even if a job throws.
//
// `runSynchronously` can unwind — a Swift runtime trap, or (under
// JavaScriptKit specifically) a JS exception crossing back into wasm.
// Clearing `isSpinning` only by falling off the end of the loop leaves
// it latched `true` on that path, and `insertJobQueue` then never
// schedules another drain: the executor is dead for the lifetime of the
// process, silently.
defer { queueState.isSpinning = false }

@kateinoigakukun kateinoigakukun Aug 25, 2026

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I think for such scenarios where an unwind happens outside of Swift's throws mechanism, the defer block won't be executed, so I don't think this change solves the issue?


while let job = self.claimNextFromQueue() {
#if compiler(>=5.9)
Expand All @@ -50,8 +59,6 @@ extension JavaScriptEventLoop {
job._runSynchronously(on: self.asUnownedSerialExecutor())
#endif
}

queueState.isSpinning = false
}

func claimNextFromQueue() -> UnownedJob? {
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