// use non-blocking sends to fill the buffer).
func timerchandrain(c *hchan) bool {
	// Note: Cannot use empty(c) because we are called
	// while holding c.timer.sendLock, and empty(c) will
	// call c.timer.maybeRunChan, which will deadlock.
	// We are emptying the channel, so we only care about
	// the count, not about potentially filling it up.
	if atomic.Loaduint(&c.qcount) == 0 {
		return false
	}
	lock(&c.lock)