[jboss-jira] [JBoss JIRA] (JGRP-1961) TCP_NIO2: message bundling can lead to corruption of msgs sent asynchronously

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13105962#comment-13105962 ] 

Bela Ban commented on JGRP-1961:
--------------------------------

Modifying {{WriteBuffers}} seems like a bad idea: a low level buffer should not be concerned about copying. I think I'll just go ahead and copy packets at the {{TCP_NIO2}} level, similar to what's currently done with send-queues in {{TCP}}. 
This code will change anyway in 4.0 when we pass a list of buffers to the send() method. Then, the JGroups header could be marshalled into a freshly created buffer as it's small anyway...

> TCP_NIO2: message bundling can lead to corruption of msgs sent asynchronously
> -----------------------------------------------------------------------------
>
>                 Key: JGRP-1961
>                 URL: https://issues.jboss.org/browse/JGRP-1961
>             Project: JGroups
>          Issue Type: Bug
>    Affects Versions: 3.6.5
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>            Priority: Critical
>             Fix For: 3.6.6
>
>
> When a message is sent with a message bundler (in {{TP}}), the output buffer in {{TP.BaseBundler}} is reused for all messages of a given bundle (say {{m1}} and {{m2}}).
> This works for {{TCP}} because a write _blocks_ and - when it returns - we're guaranteed that the buffer has been copied into an OS buffer (TCP's send window).
> However, this is different with {{TCP_NIO2}}: *an async write always returns immediately, irrespective of whether the data was written completely, partially, or not at all !*
> If a write only writes a part of its data, on returning from the write, the message bundler reuses the output buffer and can thus overwrite and corrupt buffers that are in transit, waiting to be written.
> A quick check where buffers were copied fixed the problem.
> TODO: see where we need to copy data when using a bundler. Possibly only copy if a write didn't write all of the data.



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