[jira] [Created] (CASSANDRA-14507) OutboundMessagingConnection backlog is not fully written in case of race conditions

["Sergio Bossa (JIRA)" <ji...@apache.org>]

Sergio Bossa created CASSANDRA-14507:
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             Summary: 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


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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