How to disable monitoring thread?

Hi,
My code is using some threads and in order to test that I need to wait until all threads finished, but the monitoring's thread never finish or takes long time to finish.

So I'm trying to disable the monitoring using

Mongo::Client.new([ '127.0.0.1:27017' ], :database => 'test', :monitoring => false)

but it always create a sleeping monitoring thread.

there is a way to disable the monitoring thread?