lldb hangs in a mutex in dispatch_async

Number:rdar://FB9856118 Date Originated:1/22/2022
Status: Resolved:
Product:Xcode 13.1 Product Version:
Classification:Incorrect/Unexpected Behavior Reproducible:
This has affected every version of Xcode I have used for about the last ten years. I experience it several times a week on both macOS and iOS projects. It has happened to me and my co-workers on different projects at different companies, as well as on my personal side project.

1. Debug a program that uses dispatch_async from multiple queues at the same time
2. Single step a bit and hit continue
3. Do this for a few minutes and it will reproduce

Debugger doesn’t hang

Debugger hangs. Looks like deadlock.


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