> Rails 4 is. It turns on thread safe mode by default Rails have been thread-safe for quite some time (yehuda says after fall 2008, so even before the whole me

> Rails 4 is. It turns on thread safe mode by default Rails have been thread-safe for quite some time (yehuda says after fall 2008, so even before the whole merb merger thing). (see http://yehudakatz.com/2010/08/14/threads-in-ruby-enough-already/ http://yehudakatz.com/2010/08/14/threads-in-ruby-enough-alre... comment section)