A few example of writing non-blocking thread safe method, mostly using the concept of Idempotency

http://mailinator.blogspot.com/2007/05/readerwriter-in-java-in-nonblocking.html
http://www-128.ibm.com/developerworks/java/library/j-jtp04186/index.html
http://blogs.azulsystems.com/cliff/2007/03/a_nonblocking_h.html
http://lalitpant.blogspot.com/2007/05/efficient-concurrency.html
http://en.wikipedia.org/wiki/Lock-free_and_wait-free_algorithms

Not exactly related, some project about non-blocking IO 
http://twistedmatrix.com/trac/
https://grizzly.dev.java.net/