Re: [jgroups-dev] ConnectionTableNIO

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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