function sleep(t)
  local exitTime = computer.uptime() + (t or 0)
  local events = {}
  repeat
    local d = {computer.pullSignal(exitTime - computer.uptime())}
    if d[1] ~= nil then
      events[#events+1] = d
    end
  until computer.uptime() >= exitTime
  for i = 1, #events do
    computer.pushSignal(table.unpack(events[i]))
  end
end