Re: Peterson's Algorithm in java, sequencial instruction execution
?
xmarlawx@gmail.com wrote:
....
Thank you all a lot.
I also found on an other book (operating systems) that Peterson's
solutions is not garanteed to work since some hardware platform
optimize the code in a way that could mess up the algorithm.
....
There are many layers of optimization: compiler, JVM, and hardware.
However, you should care about what is guaranteed to your program, not
about how it is achieved.
Effectively, the JLS is a contract. The Java compiler and JVM can do all
the optimization they like as long as the result follows that contract.
On the other hand, they must do whatever it takes to ensure that the
execution of the Java program does follow the JLS even in the face of
lower level optimization. That may mean, for example, adding memory
barrier instructions to code that accesses volatile fields.
I'm an expert on SPARC memory order and cache coherence issues. Even
when running on Sun systems, I've never found that knowledge in the
least bit useful for understanding Java program behavior.
You should aim to understand the ordering rules Peterson's algorithm
needs, and then look at the JLS to see what it takes to achieve those
ordering rules in Java.
Incidentally, I'm assuming you are doing this as an exercise in Java
data sharing, not for any practical use. Synchronized blocks are far
simpler, and likely to be more efficient.
Patricia