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https://issues.apache.org/jira/browse/GEODE-8195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17145806#comment-17145806
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ASF GitHub Bot commented on GEODE-8195:
---------------------------------------
bschuchardt opened a new pull request #5306:
URL: https://github.com/apache/geode/pull/5306
…tenerImpl
I've replaced the "for" loop using an implicit Iterator with one using an
explicit Iterator so that its safe "remove()" method can be used. The
Iterator method is stated as being the only safe way to modify the
collection while iterating over its contents.
I've also modified a test to validate the fix. The test forces a
failure to send two messages to an address. The failures are then
handled in the code that was throwing the
ConcurrentModificationException and, since there are two failures,
it causes two removals to be performedon the failedMessages collection.
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> ConcurrentModificationException from
> LocatorMembershipListenerImpl$DistributeLocatorsRunnable.run
> -------------------------------------------------------------------------------------------------
>
> Key: GEODE-8195
> URL: https://issues.apache.org/jira/browse/GEODE-8195
> Project: Geode
> Issue Type: Bug
> Components: membership
> Reporter: Bill Burcham
> Assignee: Bruce J Schuchardt
> Priority: Major
>
> this WAN code in
> {{LocatorMembershipListenerImpl$DistributeLocatorsRunnable.run}}:
> {code}
> Set<LocatorJoinMessage> joinMessages = entry.getValue();
> for (LocatorJoinMessage locatorJoinMessage : joinMessages) {
> if (retryMessage(targetLocator, locatorJoinMessage, attempt)) {
> joinMessages.remove(locatorJoinMessage);
> } else {
> {code}
> modifies the {{joinMessages}} set as it is iterating over the set, resulting
> in a {{ConcurrentModificationException}}.
> This bug will cause (inter-site) notification of locators (of the presence of
> a new locator) to fail early if retry is necessary. If we have to retry
> notifying any locator, and we succeed, we’ll throw the
> {{ConcurrentModificationException}} and stop trying to notify any of the
> other locators. See the _Discovery For Multi-Site Systems_ section of the
> [Overview of Multi-Site
> Caching|https://geode.apache.org/docs/guide/14/topologies_and_comm/topology_concepts/multisite_overview.html]
> documentation for an overview of the locator's role in WAN.
> Here is a scratch file that illustrates the issue, throwing
> {{ConcurrentModificationException}}:
> {code}
> import java.util.HashSet;
> import java.util.Set;
> class Scratch {
> public static void main(String[] args) {
> final Set<String> joinMessages = new HashSet<>();
> joinMessages.add("one");
> joinMessages.add("two");
> for( final String entry:joinMessages ) {
> if (entry.equals("one"))
> joinMessages.remove(entry);
> }
> }
> }
> {code}
> From looking at the Geode code, {{joinMessages}} is not used outside the loop
> so there is no need to modify it at all—I think we can simply remove this
> line:
> {code}
> joinMessages.remove(locatorJoinMessage);
> {code}
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