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https://issues.apache.org/jira/browse/KAFKA-16768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18062171#comment-18062171
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Christo Lolov commented on KAFKA-16768:
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Hello [~cyh2012aa] and [~jainamshah102]! I am happy to review efforts on this
ticket. For my understanding, did you consider a second draining in
Processor#close? Something like:
{color:#0033b3}def {color}{color:#00627a}close{color}(): Unit = {
{color:#0033b3}try {color}{
beginShutdown()
{color:#871094}thread{color}.join()
{color:#0033b3}if
{color}({color:#000000}!{color}{color:#871094}started{color}.get) {
{color:#000000}Utils{color}.swallow({color:#0033b3}this{color}.{color:#871094}logger{color}.{color:#000000}underlying{color},
{color:#000000}Level{color}.{color:#871094}ERROR{color}, () => closeAll())
}
{color:#8c8c8c} closeStraggleConnections() // <-- Second pass at draining
connections
{color}{color:#8c8c8c} {color}} {color:#0033b3}finally {color}{
{color:#871094}metricsGroup{color}.removeMetric({color:#067d17}"IdlePercent"{color},
{color:#000000}Map{color}({color:#067d17}"networkProcessor" {color}->
{color:#000000}id{color}.toString).asJava)
{color:#000000}metrics{color}.removeMetric({color:#871094}expiredConnectionsKilledCountMetricName{color})
}
}
> SocketServer leaks accepted SocketChannel instances due to race condition
> -------------------------------------------------------------------------
>
> Key: KAFKA-16768
> URL: https://issues.apache.org/jira/browse/KAFKA-16768
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 3.8.0
> Reporter: Greg Harris
> Assignee: Chang-Yu Huang
> Priority: Major
> Labels: newbie
>
> The SocketServer has threads for Acceptors and Processors. These threads
> communicate via Processor#accept/Processor#configureNewConnections and the
> `newConnections` queue.
> During shutdown, the Acceptor and Processors are each stopped by setting
> shouldRun to false, and then shutdown proceeds asynchronously in all
> instances together. This leads to a race condition where an Acceptor accepts
> a SocketChannel and queues it to a Processor, but that Processor instance has
> already started shutting down and has already drained the newConnections
> queue.
> KAFKA-16765 is an analogous bug in NioEchoServer, which uses a completely
> different implementation but has the same flaw.
> An example execution order that includes this leak:
> 1. Acceptor#accept() is called, and a new SocketChannel is accepted.
> 2. Acceptor#assignNewConnection() begins
> 3. Acceptor#close() is called, which sets shouldRun to false in the Acceptor
> and attached Processor instances
> 4. Processor#run() checks the shouldRun variable, and exits the loop
> 5. Processor#closeAll() executes, and drains the `newConnections` variable
> 6. Processor#run() returns and the Processor thread terminates
> 7. Acceptor#assignNewConnection() calls Processor#accept(), which adds the
> SocketChannel to `newConnections`
> 8. Acceptor#assignNewConnection() returns
> 9. Acceptor#run() checks the shouldRun variable and exits the loop, and the
> Acceptor thread terminates.
> 10. Acceptor#close() joins all of the terminated threads, and returns
> At the end of this sequence, there are still open SocketChannel instances in
> newConnections, which are then considered leaked.
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