code: func (c *chainView) BlockLocator(node *blockNode) BlockLocator {
  	c.mtx.Lock()
  	locator := c.blockLocator(node)
  	c.mtx.Unlock()
  	return locator
  }
docs: // BlockLocator returns a block locator for the passed block node.  The passed
  // node can be nil in which case the block locator for the current tip
  // associated with the view will be returned.
  //
  // See the BlockLocator type for details on the algorithm used to create a block
  // locator.
  //
  // This function is safe for concurrent access.