code: func (t *Tx) Flush() {
  	if t.next == t.tail {
  		// Nothing to do if there are no pushed buffers.
  		return
  	}
  
  	if t.next != t.head {
  		// The receiver will spin in t.next, so we must make sure that
  		// the slotFree bit is set.
  		t.p.write(t.next, slotFree)
  	}
  
  	t.p.writeAtomic(t.tail, t.tailHeader)
  	t.tail = t.next
  }
docs: // Flush causes all buffers pushed since the last Flush() [or Abort(), whichever
  // is the most recent] to be made visible to the receiver.