From: Eric Wong Date: 2014-12-13T02:42:08+00:00 Subject: [ruby-core:66821] Re: [Backport200 - Backport #9432] ThreadError [ Attempt to unlock a mutex which is locked by another thread ] Can you show us a small test case? Which version of Sidekiq? Note: this issue seems to not affect Ruby 2.1+ because thread.rb was rewritten in C. I looked briefly and #9132 but I'd rather deal with issues in pure Ruby or C, not C++.