Plone 5.2rc3 ValueError: signal only works in main thread

[dieter (Dieter Maurer)]

@tkimnguyen

...
File "/Users/kimnguyen/src/5.2rc3-buildout/eggs/Products.SiteErrorLog-5.3-py3.7.egg/Products/SiteErrorLog/SiteErrorLog.py", line 360, in IPubFailureSubscriber
    error_log.raising(event.exc_info)
  File "/Users/kimnguyen/src/5.2rc3-buildout/eggs/Products.PDBDebugMode-2.0-py3.7.egg/Products/PDBDebugMode/errorlog.py", line 22, in raising
    pdb.post_mortem(info[2])
  File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pdb.py", line 1622, in post_mortem
    p.interaction(None, t)
  File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pdb.py", line 344, in interaction
    signal.signal(signal.SIGINT, Pdb._previous_sigint_handler)
  File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/signal.py", line 47, in signal
    handler = _signal.signal(_enum_to_int(signalnum), _enum_to_int(handler))
ValueError: signal only works in main thread

As you can see, this is a secondary error. It is caused when Products.PDBDebugMode tries to display a traceback.

The traceback seems to indicate that the error actually comes from Python's pdb module -- or the module Python.Framework which might have been monkey patched into pdb. Apparently, the pair no longer expects that pdb can be used inside a thread.