[jboss-jira] [JBoss JIRA] Created: (JGRP-549) ConnectionTable: spurious Connection instances on concurrent connects

[Bela Ban (JIRA)]

ConnectionTable: spurious Connection instances on concurrent connects
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                 Key: JGRP-549
                 URL: http://jira.jboss.com/jira/browse/JGRP-549
             Project: JGroups
          Issue Type: Bug
            Reporter: Bela Ban
         Assigned To: Bela Ban
             Fix For: 2.6


If we have members A and B, and they don't yet have connections to each other, and start sending messages to each other at the exact same time, then we run into the following scenario:
- A attempts to connect to B (new Socket())
- B attempts to connect to A
- A accepts B's connection and adds an entry for B into its table
- B adds an entry for A into its table
- B gets the accept() from A, but doesn't add the new Connection into its table because there is already a Connection. This leads to a spurious Connection object, which will only be closed and garbage collected once A or B leaves the cluster
- We used to close Connections which were already in the table, but this lead to ping-pong effects where concurrent initial senders always closed each others connections
- Even worse: a new Socket() always creates a new Connection object and places it into the table, *regardless* of whether a Connection for a given destination already exists or not !

GOAL:
#1 Have only 1 TCP connection between any 2 members
#2 Establish a handshaking mechanism, to avoid spurious connections

SOLUTION:
- When A establishes a connection to B, A needs to get agreement from B first (and vice versa)



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