code: func (w *Waker) Assert() {
  	// Nothing to do if the waker is already asserted. This check allows us
  	// to complete this case (already asserted) without any interlocked
  	// operations on x86.
  	if atomic.LoadPointer(&w.s) == usleeper(&assertedSleeper) {
  		return
  	}
  
  	// Mark the waker as asserted, and wake up a sleeper if there is one.
  	switch s := (*Sleeper)(atomic.SwapPointer(&w.s, usleeper(&assertedSleeper))); s {
  	case nil:
  	case &assertedSleeper:
  	default:
  		s.enqueueAssertedWaker(w)
  	}
  }
docs: // Assert moves the waker to an asserted state, if it isn't asserted yet. When
  // asserted, the waker will cause its matching sleeper to wake up.