RE : Concurrent FAQ

Question

Hello,
I was reading one of the forum topics today where I came across the link for ["Concurrent Programming FAQ"|http://forums.sun.com/ann.jspa?annID=9] , there in the explanation of difference between "volatile & synchronized" is explained with the example.
volatile boolean cancelled = false;
void cancel() { cancelled = true; }
void run() {
while (!cancelled) {
doWork();
}{code}
In the above, cancelled should be volatile otherwise, the compiler can
(HotSpot -server does) hoist it out of the loop, and transform the code
into:
{code:java}
if (!cancelled)
while (true)
doWork();
{code}
And even when I was reading some article on volatile , I found out that from Java 5 , the behavior of volatile is tightened?
Can anyone help me understand these ?
Thanks in advance.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

Answer 1

The question I was trying to raise was ,
volatile boolean cancelled = false;
  void cancel() { cancelled = true; }
  void run() {
     while (!cancelled) {
        doWork();
{code}
if the varibale cancelled in the above code is not declared as volatile then how would it transform to
{code}
In the above, cancelled should be volatile otherwise, the compiler can
(HotSpot -server does) hoist it out of the loop, and transform the code
into:
if (!cancelled)
    while (true)
       doWork();{code}
And about volatile behavior after Java 5 , I read  [Volatile Keyword in Java|http://www.javamex.com/tutorials/synchronization_volatile.shtml] 
which states that "atomic updates of Volatile variables is possible after Java 5." but volatile variables are directly fetched and put into the main memory instead of
local thread memories.I find that atomic operation only. So what is the difference?
Thanks in advance.