This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
I recommend that you consider having your threads do real work -- maybe even storing the result in some public instance variable. For on some platforms, the optimizer does a good job removing useless code.