MapViewOSLogExtensions

Opinionated Swift logging of map view events for MapKit, Mapbox & MapLibre. Plays well with Xcode Instruments for millisecond timing of events.

Overview

Measure map view events such as DidFinishLoadingStyle, DidFinishRenderingMap, & DidBecomeIdle using OSLog and os.signpost.

Topics

How to Use

1. Add the package via the Swift Package Manager.

2. Add Opinionated Logs for map view.

See the enumeration mapEvents for suggested strings for your logs.

import OSLog
import MapViewOSLogExtensions

func beginMeasurementInterval() {
  // Construct the map view object
  OSLog.mapView(.begin, "measure some event")
}

func setZoomLevel(_ zoomLevel: Double) {
    // Logs to Xcode console & Xcode Instruments
    OSLog.mapView(.event, "zoomLevel: \(zoomLevel)")
    mapView.zoomLevel = zoomLevel
}

func endMeasurementInterval() {
  // This could be in an event handlers
  OSLog.mapView(.end, "measure some event")
}

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Xcode Instruments

Use Xcode Instruments for filtering logs and measuring event intervals. For more information on Xcode Instruments & signposts, see Measuring Performance Using Logging from WWDC 2018.

Xcode Instruments with the Logging template selected.

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Filter Logs 🦮

If you use the opinionated log strings, such as OSLog.mapEvents.DidFinishLoadingMap, then you filter the Instruments data by using the filter mapview. Through empirical testing, for Mapbox flavored SDKs the log analysis shows that map view events occur in this order, with DidFinishLoadingMap likely the event of when the map is displayed for the user.

00:00.286.828	[com.roblabs.log-mapview] Coordinator init, init(_:), line: 54
00:00.288.457	[com.roblabs.log-mapview] 🦮100. WillStartLoadingMap, mapViewWillStartLoadingMap(_:), line: 59
00:00.292.670	[com.roblabs.log-mapview] 🦮1. WillStartRenderingMap, mapViewWillStartRenderingMap(_:), line: 63
00:00.321.970	[com.roblabs.log-mapview] 🦮2. DidFinishLoadingStyle, mapView(_:didFinishLoading:), line: 67
00:00.531.795	[com.roblabs.log-mapview] 🦮3. DidFinishRenderingMap, mapViewDidFinishRenderingMap(_:fullyRendered:), line: 71
00:00.531.982	[com.roblabs.log-mapview] 🦮4. DidFinishLoadingMap, mapViewDidFinishLoadingMap(_:), line: 75
00:01.129.784	[com.roblabs.log-mapview] 🦮5. DidBecomeIdle, mapViewDidBecomeIdle(_:), line: 79

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Results 📈

Sample data from five runs of Geography Class on a Simulator. This sample project is making use of the OSLog extensions for map views.

Event DidFinishLoadingMap (msec)
531
499
500
529
514
mean = 514

Log vs. Signpost

Logging template with os_log and set input filter by a string.

Making observations on the data, the first entry is for 381 milliseconds, and the first entry for DidBecomeIdle is at 1258 milliseconds. The event DidFinishLoadingMap was at 651 milliseconds. Screen recording of the simulator or device can be useful to show when the map is shown to the customer.

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Logging template with os_signpost and input filter set to filter by the name of the subsystem.

This view of the os_signpost shows that the first entry is for DidBecomeIdle is at 1258 milliseconds. The event DidFinishLoadingMap was at 651 milliseconds. Screen recording of the simulator or device can be useful to show when the map is shown to the customer. The event WillStartLoadingMap started at 401 milliseconds, or about 850 milliseconds. There is also a second DidBecomeIdle event occuring several seconds later.