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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Commented] (QPID-8510) [Broker-J] Incorect use of volatile modifier for array
Date Sat, 08 May 2021 20:17:00 GMT

    [ https://issues.apache.org/jira/browse/QPID-8510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17341403#comment-17341403

ASF GitHub Bot commented on QPID-8510:

asfgit closed pull request #84:
URL: https://github.com/apache/qpid-broker-j/pull/84


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> [Broker-J] Incorect use of volatile modifier for array
> ------------------------------------------------------
>                 Key: QPID-8510
>                 URL: https://issues.apache.org/jira/browse/QPID-8510
>             Project: Qpid
>          Issue Type: Bug
>          Components: Broker-J
>            Reporter: Marek Laca
>            Priority: Minor
>              Labels: Broker, Java
> Based on Java documentation a change of volatile variable is always visible to other
threads. Hence, assignment a new array to the volatile variable guarantees the visibility
of the new array to another threads, but there is not any guarantee of the visibility of a
new element of the array. Because the insertion of a new element into the volatile array is
a change of the internal state of the array.
>  For example there is the method AMQPConnection_1_0Impl::removeTransaction:
> {code:java}
>     private volatile ServerTransaction[] _openTransactions = new ServerTransaction[16];
>     @Override
>     public void removeTransaction(final int txnId)
>     {
>         try
>         {
>             _openTransactions[txnId] = null; // There is not any  guarantee of the visibility,
when the change is propagated to another threads.
>         }
>         catch (ArrayIndexOutOfBoundsException e)
>         {
>             throw new UnknownTransactionException(txnId);
>         }
>     }
> {code}
> The same issue is in other methods of AMQPConnection_1_0Impl class.
> A concurrent collection can be used instead of the volatile array.

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