twistd errors with "reactor already installed" when dropin.cache was not created

[shengb]

When running the twistd, if dropin.cache was not created yet, it reports
twistd: The specified reactor cannot be used, failed with error: reactor already installed.

A similar issue with the ticket on:
https://twistedmatrix.com/trac/ticket/3785

[DanielALS]

Is there a solution to this ?
I had to wipe out the dropin.cache to get things working again and hit this problem.

[DanielALS]

UPDATE: Wrote too soon. This solution did not help me.

OK, found the solution to re-generate the cache:

https://twistedmatrix.com/documents/current/core/howto/plugin.html

from twisted.plugin import IPlugin, getPlugins
list(getPlugins(IPlugin))