Re: synchronized block question...

From:
Lew <noone@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 22 Sep 2008 08:56:50 -0400
Message-ID:
<dsOdnSt3xeaOC0rVnZ2dnUVZ_judnZ2d@comcast.com>
Mark Space wrote:

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...

    }
}


Be aware of lock granularity with this. The class literal is, like static
variables, global, which may be wider than you need. You get extra safety -
with a global lock there is no way to get the wrong lock - for a possible loss
in concurrent throughput overall.

The topic of threads and concurrency is a rich one. Read /Java Concurrency in
Practice/ by Brian Goetz, et al., for a good grounding in the subject. The
Javadoc package docs for java.util.concurrent
<http://java.sun.com/javase/6/docs/api/java/util/concurrent/package-summary.html>
hint at more knowledge also.

--
Lew

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