[jboss-jira] [JBoss JIRA] (JGRP-1835) DONT_LOOPBACK flag causes credit exhaustion in MFC

[Bela Ban (JIRA)]

Bela Ban created JGRP-1835:
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             Summary: DONT_LOOPBACK flag causes credit exhaustion in MFC
                 Key: JGRP-1835
                 URL: https://issues.jboss.org/browse/JGRP-1835
             Project: JGroups
          Issue Type: Bug
    Affects Versions: 3.5
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.5


When a message M is multicast by sender P and has the {{DONT_LOOPBACK}} transient flag set, it will not get looped back up the stack.
When M passes MFC on the way down, it decrements the sent credits for P. When M is received by P, the received credits are decrements and possibly credits are sent back to P.
However, M is *never received by P* because {{DONT_LOOPBACK}} causes it to be dropped.
This results in credits for P getting exhausted if we send many messages. Credit requests sent by P (every 5 s by default) do replenish P's credits, but if P sends many messages this is not enough, and slows things down.
SOLUTION:
# Don't use {{DONT_LOOPBACK}} in upper protocols or application space. JGroups itself uses it for discovery (lower protocols)
# Don't maintain credits for self; ie. P doesn't decrement or replenish credits for itself, only for others
# When sending a message tagged as {{DONT_LOOPBACK}}, decrement the *received* credits immediately and send new credits if needed



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