https://bz.apache.org/bugzilla/show_bug.cgi?id=61918
Bug ID: 61918
Summary: Nio2Endpoint may miscount connectionLimitLatch while
closing socket
Product: Tomcat 8
Version: 8.5.16
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P2
Component: Connectors
Assignee: dev@tomcat.apache.org
Reporter: ryan.f...@workday.com
Target Milestone: ----
CentOS 6.6
Tomcat 8.5.16
Connector protocol: org.apache.coyote.http11.Http11Nio2Protocol
We have noticed that the connectionCount jmx value for the nio2 connector
trends upwards on our servers during the week and never drops down to 1.
When we used netstat to trace these connections, we found the expected handful
of connections active but not the value shown by jmx. We also enabled tomcat
debug logging to see if any exceptions occurred during socket operations but
found nothing of interest.
We believe that our data center's network configuration is causing sockets to
be closed independently of the Tomcat Coyote handling but do not know what
specifically is triggering it. We also found a suspicious line in Nio2Endpoint
connector which could explain this false floor that keeps rising.
I can artificially re-create this situation by forcefully closing the socket in
a Spring MVC controller handling. Every time this endpoint is called, we
prevent Tomcat from decrementing the connection count upon close. See
Nio2Endpoint.closeSocket, line 358, only decrements the connection limit latch
when the socket is open.
Please see the attachment for:
* MyController.java - artificial recreation using Spring mvc and test framework
(easily placed in a servlet if you also include org.springframework:spring-test
module from maven)
* jmx.png - screenshot of jmx statistic we are monitoring
* connectionCounts.png - dashboard view of our server pool connection count for
a week
* Nio2Endpoint.java.patch - proposed patch for this situation
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