[jboss-jira] [JBoss JIRA] (JGRP-1871) NPEs due to non-volatile Protocol variables

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12992482#comment-12992482 ] 

Bela Ban commented on JGRP-1871:
--------------------------------

If it's only {{up_prot}} and {{down_prot}}, then that's fine as they're mostly read and only written at stack init time, so that's fast.
However, making other fields {{volatile}} can have a big impact on perf: the memory barriers established by volatile fields potentially trigger a lot of cache line flushes and (especially with false sharing) a lot of reloading. No problem if this is mostly reads, but fields with a lot of writes might slow things down a lot.
Even worse: testing this might yield good perf on one architecture, but bad perf on another; e.g. when cache line sizes differ.
Since 1998 the stack architecture has been the same and no-one has ever run into this except WF...

> NPEs due to non-volatile Protocol variables
> -------------------------------------------
>
>                 Key: JGRP-1871
>                 URL: https://issues.jboss.org/browse/JGRP-1871
>             Project: JGroups
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>    Affects Versions: 3.4.5, 3.5
>            Reporter: Paul Ferraro
>            Assignee: Paul Ferraro
>
> In WildFly a given channel is created in one thread, but is potentially started in a different thread.  Unfortunately, many of the protocol variables that are set during Protocol.init() are non-volatile. This can cause unexpected behavior as seen in WFLY-3727.
> To ensure clean initialization for multi-threaded environments like WF, all non-final variables within every JGroups' Protocol should be volatile.



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