This posts are really interesting to understand some aspects about Thread Syncronization.

http://epere4.blogspot.com/2008/04/cmo-funciona-synchronized-en-java.html

http://trevinca.ei.uvigo.es/~formella/doc/cd04/node37.html

http://developer.android.com/intl/es/guide/appendix/faq/commontasks.html#threading