MGLMapView - Mapbox注解崩溃问题排查求助

Hey there, let's break down this intermittent crash you're seeing with Mapbox. From your code and the Crashlytics context, this almost certainly boils down to thread safety issues with Mapbox's UI-related APIs.

The Root Cause #

Mapbox's MGLMapView (and its properties like annotations) is a UI component, and all interactions with it—including reading properties like annotations—must happen on the main thread. Your current code accesses self?.mapView.annotations from a global background queue (DispatchQueue.global(qos: .userInitiated)).

Most of the time this might work, but occasionally, the main thread could be updating the map's annotations at the same time your background thread is reading them. This creates a race condition, leading to the intermittent crash in Mapbox's internal code.

Fixing the Code #

To resolve this, split your work to respect thread safety rules:

1. Safely read the annotations property on the main thread
2. Handle heavy lifting (filtering, creating new annotations) in the background
3. Update the map with changes back on the main thread

Here's the adjusted code:

// First, safely fetch current annotations on the main thread
DispatchQueue.main.async {
    guard let mapView = self?.mapView, let currentAnnotations = mapView.annotations else {
        return
    }
    // Filter annotations to remove (safe to do on main thread)
    let annotsToRemove = currentAnnotations.filter { $0 is MapDangerAnnotation }
    
    // Move annotation creation to background to avoid blocking the main thread
    DispatchQueue.global(qos: .userInitiated).async {
        let annotsToAdd = dangers.map { MapDangerAnnotation(danger: $0) }
        
        // Finally, update the map on the main thread (required for Mapbox UI operations)
        DispatchQueue.main.async {
            mapView.removeAnnotations(annotsToRemove)
            mapView.addAnnotations(annotsToAdd)
        }
    }
}

Additional Verification Steps #

• Check your Crashlytics crash stack: If it shows exceptions like EXC_BAD_ACCESS or NSInternalInconsistencyException originating from Mapbox's internal annotations handling methods, that confirms the thread safety issue.
• Reference Mapbox's official docs: All UI-related operations for MGLMapView are explicitly marked as main-thread only—any off-main access is unsupported and will lead to intermittent, hard-to-reproduce crashes.

内容的提问来源于stack exchange，提问作者Libor Zapletal