[jboss-jira] [JBoss JIRA] (JGRP-1577) UNICAST / UNICAST2: add better synchronization around ReceiverEntries

[Bela Ban (JIRA)]

Bela Ban created JGRP-1577:
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             Summary: UNICAST / UNICAST2: add better synchronization around ReceiverEntries
                 Key: JGRP-1577
                 URL: https://issues.jboss.org/browse/JGRP-1577
             Project: JGroups
          Issue Type: Bug
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.3


When A gets unicast messages from B, then A creates a ReceiverEntry in its recv_table for B. The creation (or fetching of the existing ReceiverEntry) is done under a lock, however, the adding and subsequent removal of messages is not done under a lock (well, actually, adding messages to ReceiverEntry.win is locked).

What could happen is the following:
* B sends messages 1,2,3 (conn-id=5)
* B closes the connection to A
* B sends messages 1,2,3 to A (new conn-id=6)
* A receives messages 1,2,3 with conn-id=5
* A grabs the ReceiverEntry for B and starts adding 1,2,3 to win
* Messages 1-3 from B with conn-id=6 are received
* This creates a new ReceiverEntry for B
* A now starts removing and passing up messages 1-3 from B with the old conn-id 5
* A receives messages 1-3 from B with conn-id=5
* Subsequently, A also receives messages 1-3 from B with conn-id=6

Not sure if this really constitutes a bug, but I nevertheless need to take a look.
Possible solution:
* Create receiverEntry for B only *once*
* Remove ReceiverEntry for B only when the view excludes B, but *not* when B sends messages with a different conn-id
* Instead, lock on the ReceiverEntry for B when messages are received:
** When a message with a different conn-id is received, only change the contents of ReceiverEntry (e.g. conn-id, reset win etc), but *don't* remove the ReceiverEntry from recv_table and create a new one




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