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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: [OT] No movement at Debug mode
Date Fri, 26 Jan 2018 20:38:10 GMT
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All,

On 1/23/18 10:58 AM, Christopher Schultz wrote:
> The MySQL Connector/J simply has a bug. Upgrade to the latest
> version to see if they have fixed it.
> 
> I gave up trying to convince them that it was a problem and that
> they needed to fix it, because I guess they fundamentally don't
> understand what it means to want to be able to "completely
> deregister the driver and shutdown all threads".

I've been reading the release-notes for some of the more resent
versions of MySQL Connector/J, and this[1] looks interesting:

"
... [blaming Tomcat for our problems blah blah]...

The implementation of AbandonedConnectionCleanupThread has now been
improved, so that there are now four ways for developers to deal with
the situation:


* When the default Tomcat configuration is used [...] Connector/J now
detects the stopping of the web application within 5 seconds and kills
AbandonedConnectionCleanupThread

* When Tomcat's context is configured with the attribute
clearReferencesStopThreads="true" [... blah blah Tomcat does stupid
stuff blah blah ...]

* When a ServletContextListener is implemented within each web
application that calls
AbandonedConnectionCleanupThread.checkedShutdown() on context
destruction, Connector/J now, again, skips this operation if the
driver is potentially shared with other applications. No warning about
the thread being unstoppable is issued to Tomcat's error log in this
case.

* When AbandonedConnectionCleanupThread.uncheckedShutdown() is called,
the AbandonedConnectionCleanupThread is closed even if Connector/J is
shared with other applications. However, it may not be possible to
restart the thread afterwards.

"

It would be nice to know (a) how Connector/J determines (in scenario
#3) whether or not Connector/J is being "shared with other
applications". How do they stop Tomcat from logging a warning in this
case?

It would also be nice to know why (in scenario #4) the
AbandonedConnectionCleanupThread cannot be restarted if necessary.
This seems like bad design to me, and a continued failure to
understand what is going on and how developers need to interact with
the libraries they use.

I also don't understand why the thread is *always* launched.
Connector/J claims that "only queries issued with execution-timeouts
cause that thread to be launched" bug I don't have an application that
uses any query-timeouts and that thread is ALWAYS running.

- -chris

[1] https://dev.mysql.com/doc/relnotes/connector-j/5.1/en/news-5-1-41.ht
ml
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