I notice that PollingWatchService never checks the file key when it reads a directory to see if it is reading from the same directory that it started with.
I suspect that creates a potential for incorrect behavior if the directory tree is rearranged (between polls) so that the original path accesses a different directory. Specifically, if the original directory remains available via some other path, then someone watching on that path or trying to register using that path will be using a watch service that is reading the wrong directory.
