Re: [jgroups-dev] ConnectionTableNIO

Thanks for pointing this out; I made the method closeSocket() 
synchronized. I want to change this whole code anyway in the 
not-so-distant future...

Rob Eden wrote:
> Hi all -
>
> There is a race condition in ConnectionTableNIO that results in a null 
> pointer if timed just right (we actually seem to be hitting it quite a 
> bit).
>
> The closeSocket() method looks like this (comment added by me):
>
>       void closeSocket()
>       {
>
>          if (sock_ch != null)
>          {
>             try
>             {
>                // sock_ch can be null here!!!
>                if(sock_ch.isConnected() && sock_ch.isOpen()) {
>                   sock_ch.close();
>                }
>             }
>             catch (Exception e)
>             {
>                log.error("error closing socket connection", e);
>             }
>             sock_ch = null;
>          }
>       }
>
> The problem occurs when sock_ch is nulled out in between the original 
> null check and the calls to isConnected and isOpen. There are a couple 
> ways to fix the problem, including simply synchronizing the 
> closeSocket() method. However, a better (lock-free) solution might be 
> to change sock_ch to an AtomicReference. Then the closeSocket() method 
> becomes:
>
>       void closeSocket()
>       {
>  final SocketChannel sock_ch = this.sock_ch.get();
>          if (sock_ch != null)
>          {
>             try
>             {
>                if(sock_ch.isConnected() && sock_ch.isOpen()) {
>                   sock_ch.close();
>                }
>             }
>             catch (Exception e)
>             {
>                log.error("error closing socket connection", e);
>             }
>     this.sock_ch.compareAndSet( sock_ch, null );
>          }
>       }
>
> Rob
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>
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-- 
Bela Ban
Lead JGroups / JBoss Clustering team
JBoss - a division of Red Hat


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