SwiftUI Performance Audit - Corrected Findings

[alltheseas]

SwiftUI Performance Audit - Corrected Findings

⚠️ Profile-Driven Analysis with Test Requirements

This audit identified 5 confirmed SwiftUI performance issues through code analysis. All issues require Instruments profiling + failing tests before implementation.

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🟡 P1 - High Priority (3 issues)

2. Duplicate action bar task creation

Issue: damus-obn
Files: EventView.swift:116 + EventActionBar.swift:256

// EventView.swift:116 - Task #1
func make_actionbar_model(ev: NoteId, damus: DamusState) -> ActionBarModel {
    let model = ActionBarModel.empty()
    Task { await model.update(damus: damus, evid: ev) }
    return model
}

// EventActionBar.swift:256 - Task #2 (duplicate!)
.onAppear {
    Task.detached(priority: .background) {
        await self.bar.update(damus: damus_state, evid: self.event.id)
    }
}

Impact: Every timeline event creates 2 Tasks doing the same work (100 events = 200 Tasks).

Critical Dependencies:

• EventDetailBar.swift:22 relies on make_actionbar_model Task
• SelectedEventView.swift:32 gates UI on bar initialization
• Fix MUST NOT break these dependencies

Requirements:

• Add hasBeenUpdated flag to ActionBarModel
• Guard duplicate update in onAppear
• Test EventDetailBar still works
• Instruments showing reduced Task count

3. NotificationsView: DispatchQueue.main.async cleanup

Issue: damus-9dv
File: NotificationsView.swift:185-190

.background(GeometryReader { proxy -> Color in
    DispatchQueue.main.async {
        handle_scroll_queue(proxy, queue: self.notifications)
    }
    return Color.clear
})

Impact: Anti-pattern (mutates non-@published property), not infinite loop. Code health improvement.

Requirements:

• Refactor to PreferenceKey or onChange
• Test no functional regression
• Verify performance unchanged

4. EventActionBar: @State mutation from detached task

Issue: damus-fa7
Files: EventActionBar.swift:240-242, 257

@State var event_relay_url_strings: [RelayURL] = []

func updateEventRelayURLStrings() async {
    let newValue = await fetchEventRelayURLStrings()
    self.event_relay_url_strings = newValue  // ❌ @State from background
}

.onAppear {
    Task.detached(priority: .background) {
        await self.updateEventRelayURLStrings()
    }
}

Impact: Thread safety violation. @State MUST be updated on MainActor.

Note: lnurl property (line 45) is SAFE - correctly uses DispatchQueue.main.async.

Requirements:

• Thread Sanitizer failing test
• Fix with @mainactor or MainActor.run
• Thread Sanitizer passing
• Instruments validation

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🟢 P2 - Medium Priority (1 issue)

5. DateFormatter in detail views

Issue: damus-r56
Files: SelectedEventView.swift:61, IAPProductStateView.swift:89,96

func format_date(created_at: UInt32) -> String {
    let dateFormatter = DateFormatter()  // Created every call
    dateFormatter.timeStyle = time_style
    dateFormatter.dateStyle = .short
    return dateFormatter.string(from: date)
}

Impact: DateFormatter creation is expensive. Only affects detail views (NOT timeline rendering).

Requirements:

• Instruments showing DateFormatter cost
• Create static cached formatters
• Instruments showing improvement

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📋 Hard Requirements for ALL Fixes

Every PR MUST include:

1. Instruments trace showing the issue exists
2. Failing test demonstrating the problem
3. Fix that makes the test pass
4. Instruments trace showing improvement
5. No functional regressions

Test + Instruments validation = 99% merge rate

---

📚 Reference Documents

Correction History:

• .beads/AUDIT_CORRECTIONS_v3.md - Complete error analysis (16 errors across 3 rounds)
• .beads/AUDIT_CORRECTIONS_v2.md - Round 2 corrections
• .beads/AUDIT_CORRECTIONS.md - Round 1 corrections
• .beads/SwiftUI_Performance_Audit_Report.md - Original (SUPERSEDED, contains errors)

Key Lessons:

• ✅ Profile with Instruments FIRST
• ✅ Trace actual call sites
• ✅ Verify @published status for render claims
• ✅ Check ALL dependencies before suggesting changes
• ✅ Test assertions must work for edge cases
• ❌ Don't assume - counts ≠ bottlenecks without data

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🎯 Next Steps

1. Start with P0: Fix ProfileView infinite loop (damus-1gh)
2. Validate with tools: Instruments + Thread Sanitizer
3. Test-driven: Failing test → Fix → Passing test
4. Measure impact: Before/after FPS, Task counts, memory

Bottom Line: Profile-driven, test-verified fixes only. No assumptions.

[linear]

IOS-2308

[alltheseas]

1. ProfileView: DispatchQueue.main.async infinite render loop is not a real world bug.