gistfile1.rb

running = true
mutex = Mutex.new
thr = Thread.new do
  while mutex.synchronize{running}
    sleep 1
  end
end

sleep 2
#what is better
mutex.synchronize{running = false}

# or #1
running = false

# or #2
thr[:running] = false

#or #3
mutex.synchronize{thr[:running = false]}