class RSpec::Support::ReentrantMutex

Allows a thread to lock out other threads from a critical section of code, while allowing the thread with the lock to reenter that section.

Based on Monitor as of 2.2 - github.com/ruby/ruby/blob/eb7ddaa3a47bf48045d26c72eb0f263a53524ebc/lib/monitor.rb#L9

Depends on Mutex, but Mutex is only available as part of core since 1.9.1:

exists - http://ruby-doc.org/core-1.9.1/Mutex.html
dne    - http://ruby-doc.org/core-1.9.0/Mutex.html

@private