Open Radar

 
Summary:
Sometimes, when I run an app in the simulator that was already running, Xcode gets stuck. An error modal “Simulator in use” - “The Simulator can't be launched because it is already in use.” appears, and the simulator goes black. Once this happens, all subsequent attempts to Run will result in the same dialog until Xcode is restarted.

Steps to Reproduce:
Run an app in the simulator from Xcode.

Expected Results:
The expected behaviour happens 95% of the time - the app starts in the Simulator, even if the Simulator is running.

Actual Results:
Sometimes, Xcode gets stuck, displays the “The Simulator can't be launched because it is already in use” message, and must be restarted.

Regression:
This has happened in previous versions. There are Stack Overflow questions about this issue going back for quite some time.

Notes:
When Xcode is in this state:
- Quitting the Simulator doesn’t fix it.
- Activity Monitor will show “com.apple.CoreSimulator.CoreSimulatorService” running after you quit the Simulator, but even force quitting that process won’t help.
- You can still launch the Simulator from the Xcode context menu, but not from the Run command.
- There is no active debugging process in Xcode to stop.

I would be happy to do some further investigation next this happens, but have yet to figure out how to reliably trigger it, other than “keep working for an hour or two”.