SwiftUI View Tracing

[naftaly]

SwiftUI View Instrumentation

This document states the current implementation of SwiftUI View tracing.

PR: #230

The render loop

On iOS, the system for getting anything from the users code to the screen is called the render loop. It consists of a few parts, some we have control over and others we don’t. The important part is that the render loop refresh rate is pre-determined, but can change at runtime based on the state of the device. Usually, it’s 60hz which ends up being 16ms, called the frame deadline. If we miss the frame deadline, we have what is called a hitch since the system needs to wait another frame to put our content on screen.

source: Apple

Embrace View Instrumentation

• Render Loop: The duration from the first instrumented body in a render loop to the next tick of the run loop. This is a root trace.

  • name: emb-swiftui.view..render-loop
  • parent: none
  1. body: This is the duration it takes to setup the graph of what the OS will need to render.
     • name: emb-swiftui.view..body
     • parent: RenderLoop
  2. onAppear: The duration from the top of the callback to the next tick of the run loop.
     • name: emb-swiftui.view..appear
     • parent: RenderLoop
  3. onDisappear: The duration from the top of the callback to the next tick of the run loop.
     • name: emb-swiftui.view..disappear
     • parent: RenderLoop

• Time To First Render: The duration from the first time the OS initializes this View until the first time it appears on screen. This is a root trace.

  • name: emb-swiftui.view..time-to-first-render
  • parent: none

• Time To First Content Complete: The duration from the first time the OS initializes this View until the first time the user flags the content as complete. This is a root trace.

  • name: emb-swiftui.view..time-to-first-content-complete
  • parent: none
  • notes: Not available in the macro.

Example

Only the Photo surface is instrumented.

Session as a Gantt chart:

SwiftUI Performance Gantt Chart.pdf

Session in Embrace Dash:

https://dash.embrace.io/app/wnrhv/grouped_sessions/last_1_hour/54F35B20EF7C41F5ADC0668C1F34DA63/8192029933B74B9896ADD165F48C45A7@/8192029933B74B9896ADD165F48C45A7?first=9C393D0FBD3740E38DC28F60C4496358&last=2D3323E6C2FE479D867903D2C70BF2EB&source=session

API

Parameters:

• name: Required. autodetected in macro.
• attributes: Optional. key value pairs.
• contentComplete: Optional. an Equatable value that when changed, will cause the time to first content complete span to end.

View Wrapper

struct MyView: View {

	@State
	var loaded: Bool = false

	var body: some View {
		EmbraceTraceView(
	    		"MyView", 
	    		attributes: [:], 
	    		contentComplete: loaded
			) {
        			Text("Hello World")
        			Button("FInish Load") {
            				loaded = true
        			}
    			}
		}
	}
}

View Modifier

struct MyView: View {
	@State
	var loaded: Bool = false

	var body: some View {
    		Group {
        		Text("Hello World")
        		Button("Finish Load") {
            			loaded = true
        		}
    		}
    		.embraceTrace("MyView", attributes: [:], contentComplete: loaded)
	}
}

Macro. At this time, the macro cannot take any arguments. We may allow this in the future.

@EmbraceTrace
struct MyView: View {
	var body: some View {
		Text("Hello World")
	}
}

[github-actions]

Dependency Review

The following issues were found:

• ✅ 0 vulnerable package(s)
• ✅ 0 package(s) with incompatible licenses
• ✅ 0 package(s) with invalid SPDX license definitions
• ⚠️ 1 package(s) with unknown licenses.

See the Details below.

License Issues

Package.resolved

Package	Version	License	Issue Type
github.com/swiftlang/swift-syntax	509.1.1	Null	Unknown License

OpenSSF Scorecard

Package	Version	Score	Details
swift/github.com/swiftlang/swift-syntax	509.1.1	Unknown	Unknown

Scanned Files

• Package.resolved

[github-actions]

	Warnings
⚠️	No CHANGELOG entry added.

Generated by 🚫 Danger Swift against 63929b6

[codecov]

Codecov Report

Attention: Patch coverage is 76.80764% with 170 lines in your changes missing coverage. Please review.

Project coverage is 88.36%. Comparing base (1710885) to head (63929b6).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...rces/EmbraceMacros/Plugins/EmbraceTraceMacro.swift	0.00%	117 Missing ⚠️
Sources/EmbraceCore/SwiftUI/EmbraceTraceView.swift	87.68%	17 Missing ⚠️
...EmbraceCore/SwiftUI/EmbraceTraceViewModifier.swift	0.00%	13 Missing ⚠️
...eCore/SwiftUI/Internal/EmbraceTraceViewState.swift	40.00%	9 Missing ⚠️
...Core/SwiftUI/Internal/EmbraceTraceViewLogger.swift	92.75%	5 Missing ⚠️
Sources/EmbraceConfigInternal/EmbraceConfig.swift	0.00%	3 Missing ⚠️
...figInternal/EmbraceConfigurable/RemoteConfig.swift	0.00%	3 Missing ⚠️
...es/EmbraceMacros/Plugins/EmbraceMacrosPlugin.swift	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #230      +/-   ##
==========================================
- Coverage   88.75%   88.36%   -0.40%     
==========================================
  Files         448      458      +10     
  Lines       30513    31286     +773     
==========================================
+ Hits        27082    27646     +564     
- Misses       3431     3640     +209     

Files with missing lines	Coverage Δ
...onfigurable/RemoteConfig/RemoteConfigPayload.swift	100.00% <100.00%> (ø)
...figuration/EmbraceConfigurable/DefaultConfig.swift	84.21% <100.00%> (+0.87%)	⬆️
...ore/SwiftUI/Internal/EmbraceTraceViewContext.swift	100.00% <100.00%> (ø)
...urable/RemoteConfig/RemoteConfigPayloadTests.swift	100.00% <100.00%> (ø)
...eCoreTests/SwiftUI/EmbraceTraceViewPerfTests.swift	100.00% <100.00%> (ø)
...braceCoreTests/SwiftUI/EmbraceTraceViewTests.swift	100.00% <100.00%> (ø)
Tests/EmbraceMacrosTests/EmbraceMacrosTests.swift	100.00% <100.00%> (ø)
Tests/TestSupport/EditableConfig.swift	90.00% <100.00%> (+0.71%)	⬆️
...ts/TestSupport/Mocks/MockEmbraceConfigurable.swift	55.75% <100.00%> (+3.82%)	⬆️
Sources/EmbraceConfigInternal/EmbraceConfig.swift	71.76% <0.00%> (-2.63%)	⬇️
... and 7 more

... and 2 files with indirect coverage changes

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