Java Memory Model: reordering and concurrent locks

Question

The java meomry model mandates that synchronize blocks that synchronize on the same monitor enforce a before-after-realtion on the variables modified within those b

Answer 1

Yanamon, I am not sure you are correct - but for different reasons than the argument you are making.

The unguardedVariable variable may be re-ordered in thread "a" such that its value is set to 10 after memoryBarrier is set to true.

"There is no guarantee that operations in one thread will be performed in the order given by the program, as long as the reordering is not detectable within that thread - even if the reordering is apparent to other threads"

Java Concurrency in Practise, Brian Goetz, p34

UPDATED: what I said is true in the case of the old memory model. So, if you want write-once-run-anywhere then my argument stands. However, in the new memory model, it is not the case as the semantics surrounding re-ordering of non-volatile variables in the presence of volatile access has become stricter (see http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#volatile).