Re: sync on local variable

From:

Roedy Green <see_website@mindprod.com.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 25 Mar 2010 10:27:31 -0700

Message-ID:

<a47nq51m191qtusob63173kp3lgk3jafla@4ax.com>

On Thu, 25 Mar 2010 00:06:56 -0400, Eric Sosman
<esosman@ieee-dot-org.invalid> wrote, quoted or indirectly quoted
someone who said :

  AppToWatch row;
  synchronized ( ALL_ROWS )
                 {
                 row = ALL_ROWS.get( rowIndex );
                 state = row.getState();
                 }
...
   synchronized ( row )
                     {
                     url = row.getVersionURL();
                     marker = row.getMarker();
                     }

Are you sure you didn't misread IntelliJ's complaint? The
thing that strikes me as odd about this code is that there are
three method calls made on row's object, only two of which are
synchronized on that object. It's conceivable that this is all
right, but it sure looks strange to me -- and perhaps IntelliJ
thinks it peculiar, too.

I corrected the code to read:

   AppToWatch row;
   synchronized ( ALL_ROWS )
                  {
                  row = ALL_ROWS.get( rowIndex );
                  synchronized ( row )
                      {
                      state = row.getState();
                      }
                  }
...
    synchronized ( row )
                      {
                      url = row.getVersionURL();
                      marker = row.getMarker();
                      }

Now I get TWO message about synchorizing on row.
--
Roedy Green Canadian Mind Products
http://mindprod.com

If you tell a computer the same fact in more than one place, unless you have an automated mechanism to ensure they stay in sync, the versions of the fact will eventually get out of sync.