[jboss-jira] [JBoss JIRA] Commented: (JGRP-590) FC: messages > max_credits will block forever

[Bela Ban (JIRA)]

    [ http://jira.jboss.com/jira/browse/JGRP-590?page=comments#action_12375615 ] 
            
Bela Ban commented on JGRP-590:
-------------------------------

The above description is not correct: when we block on credits, as soon as we have received credits, we actually do send the blocked message, but the credits might become negative. Example:
- credits=50000
- we send message M1 with 70000 bytes
- we block until new credits are received
- even if the new credits + remaining credits are 50000, we *send* the message
- now (remaining) credits are -20000
- the next message will block again

So, while we don't block forever, we should still implement the proposed changes, as they prevent misconfiguration, and too many blockings due to messages which are too large

> FC: messages > max_credits will block forever
> ---------------------------------------------
>
>                 Key: JGRP-590
>                 URL: http://jira.jboss.com/jira/browse/JGRP-590
>             Project: JGroups
>          Issue Type: Task
>            Reporter: Bela Ban
>         Assigned To: Bela Ban
>             Fix For: 2.6, 2.5.1, 2.4.1 SP5
>
>
> FC.down checks for the message size. If that size is greater than the credits left, we block until we get more credits from the receiver(s). However, if the message size is greater than *max_credits*, we will *never* have more than max_credits available to send the message, so we'd block forever !
> To prevent running into this, we need to check (at startup time) in FC that
> - a fragmentation protocol is available (somewhere above the FC protocol) 
> - that the max fragmentation size of the fragmentation protocol is smaller than max_credits
> We should also log a (fatal) error message if we receive a message whose size is greater than max_credits (this should *not* happen anymore though after the proposed change above)

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