Re: [javagroups-users] IllegalArgumentException in UNICAST

[Bela B. <be...@ya...>]

Lenny Phan wrote:
> Thanks!  The scenario described below is exactly what's intermittently 
> happening.
> I'm not sure I understand how alternatives #1 and #2 might work for 
> this race condition?

#1 When connect() returned, we are guaranteed that the view has been 
received up and down the stack, including UNICAST. UNICAST updates its 
membership, so the issue you're seeing won't happen.

You could also send down an event Event.ENABLE_UNICASTS_TO (with the 
unicast destination you want to send to), this would prevent UNICAST 
from throwing the exception when sending a message to a dest T which is 
(not yet) in the membership list.

> Bela Ban wrote:
>> No. It could still happen, though less likely. Since pass the view up 
>> the stack first, then down, if the view was placed onto the queue and 
>> processed *before* we send the view down (and thus update UNICAST's 
>> membership), you'd still see the same issue.
>>
>> The offending code is at GMS.java (ll 505-506):
>>
>> 502           // Send VIEW_CHANGE event up and down the stack:
>> 503           Event view_event=new Event(Event.VIEW_CHANGE, 
>> new_view.clone());
>> 504            // changed order of passing view up and down 
>> (http://jira.jboss.com/jira/browse/JGRP-347)
>> 505            up_prot.up(view_event);
>> 506           down_prot.down(view_event); // needed e.g. by failure 
>> detector or UDP
>>
>> Line 505 passes the event up the stack, 506 down the stack. If we 
>> swap the lines, your code will be fine. However, Vladimir swapped 
>> them before, to fix JGRP-347. I've pinged him to find out the reason 
>> why he did that. If it turns out we can swap those lines back, your 
>> code is guaranteed to work, otherwise we'll have to look at 
>> alternatives.
>>
>> Some alternatives that come to mind:
>>
>> #1 Set a flag to true once JChannel.connect() has returned
>> #2 Implement the ChannelListener.channelConnected() callback

-- 
Bela Ban
Lead JGroups / JBoss Clustering team
JBoss - a division of Red Hat