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Fix NSHostingView async rendering cycle on macOS #898

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Merged
Kyle-Ye merged 1 commit into from
Jun 7, 2026
Merged

Fix NSHostingView async rendering cycle on macOS #898

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51 changes: 26 additions & 25 deletions Sources/OpenSwiftUI/Integration/Hosting/AppKit/View/NSHostingView.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -421,28 +421,22 @@ open class NSHostingView<Content>: NSView, XcodeViewDebugDataProvider where Cont
// TODO
NSAnimationContext.runAnimationGroup { context in
context.allowsImplicitAnimation = false
isUpdating = true
// TODO
render(targetTimestamp: nil)
// TODO
isUpdating = false
// TODO
if needsDeferredUpdate {
if !viewGraph.updateRequiredMainThread {
if isLinkedOnOrAfter(.v3) {
if startAsyncRendering() {
needsDeferredUpdate = false
}
var iteration = 0
repeat {
needsDeferredUpdate = false
isUpdating = true
render(targetTimestamp: nil)
isUpdating = false
if needsDeferredUpdate,
!viewGraph.updateRequiredMainThread,
isLinkedOnOrAfter(.v3),
!viewGraph.mayDeferUpdate {
if startAsyncRendering() {
needsDeferredUpdate = false
}
}
}
if needsDeferredUpdate {
onNextMainRunLoop { [weak self] in
guard let self else { return }
setNeedsUpdate()
}
needsDeferredUpdate = false
}
iteration += 1
} while needsDeferredUpdate && iteration < 8

@augmentcode augmentcode Bot Jun 7, 2026 •
edited
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If needsDeferredUpdate remains true after hitting the iteration < 8 cap, there’s no follow-up scheduling (e.g. another setNeedsUpdate()), so the view could drop an update and get stuck. Is it guaranteed that this condition can’t persist beyond the loop?

Severity: medium

Fix This in Augment

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}
}

Expand Down Expand Up @@ -782,8 +776,12 @@ open class NSHostingView<Content>: NSView, XcodeViewDebugDataProvider where Cont
static func defaultViewGraphOutputs() -> ViewGraph.Outputs { .defaults }

func setNeedsUpdate() {
needsUpdateConstraints = true
needsLayout = true
if isUpdating {
needsDeferredUpdate = true
} else {
needsUpdateConstraints = true
needsLayout = true
}
}

// MARK: - Window Notification Handlers
Expand Down Expand Up @@ -954,10 +952,13 @@ extension NSHostingView: ViewRendererHost {

if adjustedDelay >= 0.25 {
setUpdateTimer(delay: adjustedDelay)
} else if isUpdating {
needsDeferredUpdate = true
} else {
} else if adjustedDelay == 0 || !isUpdating {
setNeedsUpdate()
} else {
onNextMainRunLoop { [weak self] in
guard let self else { return }
setNeedsUpdate()
}
}

// TODO: Notify delegate
Expand Down
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