ruby console spinner

spinner.rb

def with_spinner
  finished = false
  working   = Mutex.new
  spinner = Thread.new do
    loop do
      break if working.synchronize {finished}
      ["|","/","-","\\"].each do |glyph|
        print "\r#{glyph}"
        sleep 0.07
        print "\b"
      end
    end
  end
  define_singleton_method(:puts) { |s| super("\b#{s}") }
  yield
  working.synchronize{ finished = true }
  spinner.join
  STDOUT.flush
end


puts "A"
with_spinner{ sleep 2; puts "starting..."; sleep 2 ; puts "stopped"; }
puts "B"

# wanted output while spinning:
# A
# /
# B

# wanted output after:
# A
# started...
# stopped
# B

# output without overriding puts method (line#14)
# A
# |starting...
# |stopped
# B

This little helper method works nicely for displaying a spinner until the block is finished. The only way I could get the block to print was to override the puts method in the block (line 14) to move the cursor back before printing. Is there a nice way to achieve this?