dalli: (RuntimeError) "multi_response has completed"

I got this error once. I saw that this exception was raised

https://github.com/mperham/dalli/blob/57943358b4701d814d861409cc01dab237290fe6/lib/dalli/server.rb#L140

Just want to know in what case this might happen?

/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/server.rb:140:in `multi_response_nonblock'
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/options.rb:42:in `block in multi_response_nonblock' 
/home/ubuntu/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/options.rb:41:in `multi_response_nonblock'
 /home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:413:in `block (4 levels) in get_multi_yielder' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:409:in `each'
 /home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:409:in `block (3 levels) in get_multi_yielder' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:385:in `loop'
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:385:in `block (2 levels) in get_multi_yielder'
 /home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/ring.rb:51:in `lock' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:372:in `block in get_multi_yielder' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:316:in `call' /home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:316:in `perform' 

/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:370:in `get_multi_yielder'
 /home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:65:in `block in get_multi' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:64:in `tap' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p247@spaghetti/ruby/2.0.0/gems/dalli-2.7.0/lib/dalli/client.rb:64:in `get_multi'