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https://issues.apache.org/jira/browse/GEODE-9122?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17320377#comment-17320377
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ASF subversion and git services commented on GEODE-9122:
--------------------------------------------------------
Commit 69834d5e81875850b1dde759d04a485f8b3aa461 in geode's branch
refs/heads/feature/GEODE-7665 from Alberto Gomez
[ https://gitbox.apache.org/repos/asf?p=geode.git;h=69834d5 ]
GEODE-9122: Avoid possible ConcurrentModificationException with
group-transaction-events=true (#6278)
When group-transaction-events is set to true
if the SerialGatewaySenderQueue.peekEventsFromIncompleteTransactions
or ParallelGatewaySenderQueue.peekEventsFromIncompleteTransactions contain
more than one TransactionId, and one of them is removed,
the ConcurrentModificationException will occur.
> Setting group-transaction-events=true can cause
> ConcurrentModificationExceptions
> --------------------------------------------------------------------------------
>
> Key: GEODE-9122
> URL: https://issues.apache.org/jira/browse/GEODE-9122
> Project: Geode
> Issue Type: Bug
> Components: wan
> Reporter: Barrett Oglesby
> Assignee: Alberto Gomez
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.15.0
>
>
> The
> SerialWANStatsDUnitTest.testReplicatedSerialPropagationHAWithGroupTransactionEvents
> test can throw a ConcurrentModificationException like:
> {noformat}
> [warn 2021/04/04 02:55:53.253 GMT <Event Processor for GatewaySender_ln>
> tid=0x15d] An Exception occurred. The dispatcher will continue.
> java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445)
> at java.util.HashMap$KeyIterator.next(HashMap.java:1469)
> at
> org.apache.geode.internal.cache.wan.serial.SerialGatewaySenderQueue.peekEventsFromIncompleteTransactions(SerialGatewaySenderQueue.java:476)
> at
> org.apache.geode.internal.cache.wan.serial.SerialGatewaySenderQueue.peek(SerialGatewaySenderQueue.java:453)
> at
> org.apache.geode.internal.cache.wan.AbstractGatewaySenderEventProcessor.processQueue(AbstractGatewaySenderEventProcessor.java:518)
> at
> org.apache.geode.internal.cache.wan.serial.SerialGatewaySenderEventProcessor.run(SerialGatewaySenderEventProcessor.java:223)
> {noformat}
> If the SerialGatewaySenderQueue.peekEventsFromIncompleteTransactions contains
> more than one TransactionId, and one of them is removed, the
> ConcurrentModificationException will occur.
> Both the SerialGatewaySenderQueue and ParallelGatewaySenderQueue
> peekEventsFromIncompleteTransactions have the same implementation.
> These methods do:
> {noformat}
> while (true) {
> 1. -> for (TransactionId transactionId : incompleteTransactionIdsInBatch) {
> ...
> if (...) {
> ...
> 2. -> incompleteTransactionIdsInBatch.remove(transactionId);
> }
> }
> }
> {noformat}
> The for-each loop (1) cannot be paired with the remove from the
> incompleteTransactionIdsInBatch set (2). As soon as the remove is called, the
> ConcurrentModificationException will be thrown the next time through the
> loop. Since this for loop is in a while (true) loop, it is an infinite loop.
> One way to address this would be to use an Iterator and call remove on the
> Iterator like:
> {noformat}
> 1. -> for (Iterator<TransactionId> i =
> incompleteTransactionIdsInBatch.iterator(); i.hasNext();) {
> TransactionId transactionId = i.next();
> ...
> 2. -> i.remove();
> {noformat}
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