class RSpec::Core::ReentrantMutex

@private
dne - ruby-doc.org/core-1.9.0/Mutex.html<br>exists - ruby-doc.org/core-1.9.1/Mutex.html<br>Depends on Mutex, but Mutex is only available as part of core since 1.9.1:
Based on Monitor as of 2.2 - github.com/ruby/ruby/blob/eb7ddaa3a47bf48045d26c72eb0f263a53524ebc/lib/monitor.rb#L9<br><br>while allowing the thread with the lock to reenter that section.
Allows a thread to lock out other threads from a critical section of code,

def enter
  @mutex.lock if @owner != Thread.current
  @owner = Thread.current
  @count += 1
end

def exit
  @count -= 1
  return unless @count == 0
  @owner = nil
  @mutex.unlock
end

def initialize
  @owner = nil
  @count = 0
  @mutex = Mutex.new
end

def synchronize
  enter
  yield
ensure
  exit
end

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