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https://issues.apache.org/jira/browse/CASSANDRA-14507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16506789#comment-16506789
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Dinesh Joshi commented on CASSANDRA-14507:
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[~sbtourist] thank you for the bug report.
{quote}3) The writer threads are scheduled back and add to the backlog, but the
channel state is READY at this point, so those writes would sit in the backlog
and expire.
{quote}
I am not clear on how the messages would simply sit in the backlog queue and
expire? Wouldn't they be picked up by the
{{MessageOutHandler::channelWritabilityChanged}} and then get drained? What am
I missing here?
> OutboundMessagingConnection backlog is not fully written in case of race
> conditions
> -----------------------------------------------------------------------------------
>
> Key: CASSANDRA-14507
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14507
> Project: Cassandra
> Issue Type: Bug
> Components: Streaming and Messaging
> Reporter: Sergio Bossa
> Priority: Major
>
> The {{OutboundMessagingConnection}} writes into a backlog queue before the
> connection handshake is successfully completed, and then writes such backlog
> to the channel as soon as the successful handshake moves the channel state to
> {{READY}}.
> This is unfortunately race prone, as the following could happen:
> 1) One or more writer threads see the channel state as {{NOT_READY}} in
> {{#sendMessage()}} and are about to enqueue to the backlog, but they get
> descheduled by the OS.
> 2) The handshake thread is scheduled by the OS and moves the channel state to
> {{READY}}, emptying the backlog.
> 3) The writer threads are scheduled back and add to the backlog, but the
> channel state is {{READY}} at this point, so those writes would sit in the
> backlog and expire.
> Please note a similar race condition exists between
> {{OutboundMessagingConnection#sendMessage()}} and
> {{MessageOutHandler#channelWritabilityChanged()}}, which is way more serious
> as the channel writability could frequently change, luckily it looks like
> {{ChannelWriter#write()}} never gets invoked with {{checkWritability}} at
> {{true}} (so writes never go to the backlog when the channel is not writable).
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