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https://issues.apache.org/jira/browse/GEODE-4072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16297464#comment-16297464
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nabarun commented on GEODE-4072:
--------------------------------
Order of execution for this race condition to occur.
# _dispatchBatch is trying to dispatch a batch of events but was somehow
unsuccessful
# It silently decides that the remote server may not be ready so it wants to
retry
# Same time we decide to stop the SerialGatewaySenderEventProcessor hence we
call the Stopper Thread.
# Before the threads are started on all the senders / dispatchers it sets the
isStopped flag for the SerialGatewaySenderEventProcessor to true.
# Then the _dispatchBatch method which was in retry mode makes a getConnection
call to get the connection. This method does a check on the
SerialGatewaySenderEventProcessor's isStopped flag. It sees that the flag is
set and this return null.
# This null is stored in the global variable connection for the dispatcher.
# Now that the _dispatchBatch method calls sees that the connection is null it
should raise an exception and destroyConnection.
# Meanwhile there was a AckThreadReader that was running and the stopper thread
for the event processor wants to stop it, but since the connection global
variable was set to null by the get connection method call by _disptachBatch.
# Hence the shutDownAckReaderThreadConnection is executed on null and hence the
AckReaderThread continues to keep running - being stuck on socketRead0.
# But the problem is that the AckReaderThread acquire a
connectionLifeCycle.readLock. to readAcknowledgement, but the destroyConnection
calls from the stopper thread and _dispatchBatch's exception handling code
needs a connectionLifeCycleLock.writeLock which they can't because readLock is
held by the AckReaderThread, causing a deadlock
> Race condition in AckReaderThread.shutdown
> -------------------------------------------
>
> Key: GEODE-4072
> URL: https://issues.apache.org/jira/browse/GEODE-4072
> Project: Geode
> Issue Type: Bug
> Components: wan
> Reporter: nabarun
> Assignee: nabarun
> Fix For: 1.4.0
>
>
> *+Issue+*
> {code:title=AckReaderThread.java}
> if (connection != null) {
> Connection conn = connection;
> shutDownAckReaderConnection();
> if (!conn.isDestroyed()) {
> conn.destroy();
> sender.getProxy().returnConnection(conn);
> }
> }
> {code}
> The global connection variable may be set to null before it is assigned to
> the local variable, resulting in NPE.
> *Solution*:
> --set the local variable to the connection variable and use that local
> variable for null checks.
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