class ActiveRecord::ConnectionAdapters::ConnectionPool::Queue

def wait_poll(timeout)
  @num_waiting += 1
  t0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  elapsed = 0
  loop do
    ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
      @cond.wait(timeout - elapsed)
    end
    return remove if any?
    elapsed = Process.clock_gettime(Process::CLOCK_MONOTONIC) - t0
    if elapsed >= timeout
      msg = "could not obtain a connection from the pool within %0.3f seconds (waited %0.3f seconds); all pooled connections were in use" %
        [timeout, elapsed]
      raise ConnectionTimeoutError, msg
    end
  end
ensure
  @num_waiting -= 1
end