func Sleep(d Duration)

var asynctimerchan = godebug.New("asynctimerchan")

// syncTimer returns c as an unsafe.Pointer, for passing to newTimer.
// If the GODEBUG asynctimerchan has disabled the async timer chan
// code, then syncTimer always returns nil, to disable the special
// channel code paths in the runtime.
func syncTimer(c chan Time) unsafe.Pointer {
	// If asynctimerchan=1, we don't even tell the runtime

	// If the client falls behind while reading, we drop ticks
	// on the floor until the client catches up.
	c := make(chan Time, 1)
	t := (*Ticker)(unsafe.Pointer(newTimer(when(d), int64(d), sendTime, c, syncTimer(c))))
	t.C = c
	return t
}

// Stop turns off a ticker. After Stop, no more ticks will be sent.
// Stop does not close the channel, to prevent a concurrent goroutine