Crash in SDLChoiceSetManager due to multiple threads accessing nonatomic NSSets

[NicoleYarroch]

Bug Report

Experienced a crash in SDLChoiceSetManager due to multiple threads accessing nonatomic NSMutableSets preloadedMutableChoices and pendingMutablePreloadChoices.

Reproduction Steps

This bug is difficult to reproduce due to this being a race condition. I've only seen this bug once.

1. Create multiple choice sets using the Screen Manager API.
2. Connect app to head unit.

Expected Behavior

The app does not crash

Observed Behavior

The app does crash due to multiple threads trying to access preloadedMutableChoices and pendingMutablePreloadChoicesin the SDLChoiceSetManager.

OS & Version Information

• iOS Version: n/a
• SDL iOS Version: 6.5
• Testing Against: n/a

Test Case, Sample Code, and / or Example App

Testing with Livio music player.