Re: synchronized block question...

From:

Mark Space <markspace@sbcglobal.net>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 21 Sep 2008 21:01:22 -0700

Message-ID:

<gb75b1$ie8$1@registered.motzarella.org>

grz01 wrote:

So a safer method would be to use a value like: new Date()
for semaphore, that is not likely to get covertly duplicated-by-
caching by the JVM then...?

Lew gave you some good ideas.

1. make the object "final". That way Java will give you an error if you
try to replace it.

2. the conventional object to lock on when you just need a random object
to lock is Object.

And Joshua said:

3. yes, definitely look at Semaphore, Lock, and other stuff in
java.util.concurrent.

Lastly, consider locking on some object you already have, rather than
making a special object to lock on. I think synchronizing on the class
object is the same as synchronizing on a static object, and much harder
to mess up. (Joshua did mention class literals too, now that I look.)

public class ProcessData extends org.apache.struts.action.Action {

     public ActionForward execute(ActionMapping mapping, ActionForm
form,
             HttpServletRequest request, HttpServletResponse response)
             throws Exception {

         // ...some code...
         synchronized ( ProcessData.class )
         {
           // ...more code...
         }
         //...more code...

     }
}