Re: Broken Failover Logic in Livetribe SLP

> There is a bug in the SLP Server code that causes a problem...
>
> TO REPRODUCE (using the standard directory server, and the client and
> servers here: http://livetribe.codehaus.org/SLP-Examples-JMX
>
> (1) Start the directory server, client and server. They should all
> find each other
> (2) Kill the directory server and the client
> (3) Start the directory server, then the client
> ** the client will not find the server**
>
> WHY
>
> When the directory server restarts, it sends advertising messages.
> However, the server doesn't respond as it thinks it has already
> registered with that server. In the meantime, it advertises itself via
> multicast. When the client is restarted, it finds the directory server
> and interrogates it, so doesn't read the server's multicast messages.
>
> CODE
>
> In DirectoryAgentInfoCache, the following method is called when a
> server receives a directory server advertisement:
>
>   public void handle(DirectoryAgentInfo directoryAgent)
>   {
>       if (directoryAgent.isShuttingDown())
>       {
>           DirectoryAgentInfo removed =  
> remove(directoryAgent.getKey());
>           if (removed != null)  
> notifyDirectoryAgentDied(directoryAgent);
>       }
>       else
>       {
>           DirectoryAgentInfo existing = add(directoryAgent);
>           if (existing == null)
> notifyDirectoryAgentBorn(directoryAgent); //*******REMOVE if(existing
> == null)*******
>       }
>   }
>
> In the above situation, existing is not null when the restarted
> directory agent sends its advertisements, so the server never
> responds. To fix this, remove 'if (existing == null)' so the server
> always tells the directory agent what services it has.
>
> Please let me know if you need any more clarification,
>
> Thanks,
>
> Nick
>
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