minecraft server 14w17a "something is taking too long!" related issue

The game is very laggy/bad framerate for any player on the server, or otherwise when joining they are put into an empty space and can't move/do anything, then eventually kicked off the game. This happens for both customised worlds and randomly generated worlds. I have hosted previous versions of minecraft on this machine before without experiencing these issues, so I'm certain that it is related to this particular version of the server.

upon debugging, i get some crazy warnings. I attached the log so you can see for yourself what the problem is. thanks