→⎕LC after setting stops while tracing causes unrecoverable hang

[mkromberg]

Describe the issue you are having

→⎕LC entered from the session while tracing, after setting stops, makes the tracer disappear, but control is lost

Did you connect to an already running interpreter or start the interpreter from RIDE?

Started 18.1.39958 under Windows

How do you reproduce the issue?

)ed foo, create a function with a few lines of code
trace foo
once foo appears, set a stop near the end of the function (if you don't set a stop, all is well)
→⎕lc

Paste the contents of Help → About (Shift+F1)

IDE:
  Version: 4.4.3474
  Platform: Win32
  Date: 2021-01-29 17:14:19 +0100
  Git commit: 9105fc792fb7f507a9b66f0265cd436d2b63565f
  Preferences:{
    "floatSingle":"0",
    "floating":"1",
    "kbdLocale":"da_DK",
    "prefixKey":"<",
    "selectedExe":"C:\\Program Files\\Dyalog\\Dyalog APL-64 18.0 Unicode\\dyalog.exe"
  }

Interpreter:
  Version: 18.1.39958
  Platform: Windows-64
  Edition: Unicode/64
  Date: Feb  2 2021 at 21:10:02

[e9gille]

Looks like a race condition when using floating windows.

[e9gille]

Probably causing #557

[e9gille]

Fixed by #656