Re: [jetty-users] JDBCSessionManager dirty operations

[" \"\"" <lord.buddha@xxxxxxxxx>]

Indeed, tomcat uses a concurrent hash map and no explicit synchronisation when accessing/updating session attributes.

And in fact tomcat only uses synchronized in two places, when expiring the session and when fire events to session listeners.

Yeah, I hear that synchronisation "is not such an overhead", but then put large load on big multi socket multicore box and watch it completely fail to scale to the available hardware.

On 27 February 2014 20:35, "" <lord.buddha@xxxxxxxxx> wrote:

Ouch.  Just looked at the   AbstractSessionManager...   Such synchronisation is the tip of the iceberg.  

I wonder if there really needs to be this amount of synchronisation when the order of the requests coming in that might affect a session can be quote arbitrary in themselves.   On AbstractSessionManager synchronisation protection on _attributes is perhaps overkill when a ConcurrentHashMap could be used instead.

On 27 February 2014 20:02, "" <lord.buddha@xxxxxxxxx> wrote:

I don't believe the synchronised block is useful here.   Synchronised should be used to stop things breaking, not to protect against something that is occasionally inefficient.

So this is sufficient and will avoid inconsistent synchronization warnings...

   @Override


   public void removeAttribute(String name) {



      if(getAttribute(name)){
         super.removeAttribute(name);
         _dirty = true;
      }   



   }

On 27 February 2014 10:40, Jan Bartel <janb@xxxxxxxxxxx> wrote:

Cemo,

This will need some refactoring of the implementation of the session
interface, but I'm not opposed to looking into it.

Can you open a bug for this please and assign to me?

thanks
Jan

On 27 February 2014 06:25, Cemo <cemalettin.koc@xxxxxxxxx> wrote:
> Hi,
>
> Current org.eclipse.jetty.server.session.JDBCSessionManager has
> removeAttribute as this:
>
>   public void removeAttribute (String name)
>
>  {
>       super.removeAttribute(name);
>
>
>
>      _dirty=true;
>  }
>
>
> This has a side effect because of making dirty for every removing operation.
> This is causing a lot of trouble because each jstl set ( c:set ) call in JSP
> pages is also calling removeAttribute internally. What I am suggesting is
> that something like this:
>
>
>    @Override
>    public void removeAttribute(String name) {
>
>
>
>       synchronized (this){
>          Object attribute = getAttribute(name);
>
>
>
>          if(attribute != null){
>
>
>
>             super.removeAttribute(name);
>
>
>
>             _dirty = true;
>          }
>       }
>    }
>
> public
>
>
> https://gist.github.com/cemo/9236abe34d2b126242ad
>
> What do you think?
>

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>



--
Jan Bartel <janb@xxxxxxxxxxx>
www.webtide.com
'Expert Jetty/CometD developer,production,operations advice'
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