[jboss-jira] [JBoss JIRA] Resolved: (JGRP-966) UNICAST: multiple SEND_FIRST_SEQNO messages cause message loss

UNICAST: multiple SEND_FIRST_SEQNO messages cause message loss -------------------------------------------------------------- Key: JGRP-966 URL: https://jira.jboss.org/jira/browse/JGRP-966 Project: JGroups Issue Type: Bug Reporter: Bela Ban Assignee: Bela Ban Fix For: 2.6.10.merge, 2.8 If we have A and B: A: 5 6 7 8 9 and B: - - A sends #5 - # 9 to B, then B will send a SEND_FIRST_SEQNO to A per message for a total of 5 - A resends #5 with a conn-id of (say) 322649 - B creates the receiver window for A with conn-id=322649 and adds #5, then removes it and acks #5 - A receives an ack for #5 and removes #5 from it sender window - A then receives the next (stale) SEND_FIRST_SEQNO request - A now resends #6 with a conn-id=322649 ---> B drops #6 (and all subsequent messages) with conn-id=322649 ! ==> The simple solution is to not drop messages with a conn-id if the receiver window already exists *and* the conn-ids match Potential issue: what if we re-send #6 with conn-id=322649 *before* #5 with conn-id=322649 ? - A message on the sender side is only removed if it received an ACK from the receiver - Reception of an ACK means the receiver window was created - When we receive ACK(5), that means we created a receiver window on B with conn-id=322649 and added #5 - Therefore the re-sending of #6 with conn-id=322649 will *never* happen before the receiver window on B is created for #5 and conn-id=322649 !