On Tue, Jul 16, 2019 at 6:47 PM Manuel Dominguez Sarmiento
wrote:
> Hi, we had been running Tomcat 9.0.17 for quite some time on our high-load
> production servers, using the attached server.xml configuration.
>
> Upon upgrading to 9.0.21 we started experiencing many random deadlocks. We
> run performance advertising campaigns, and our conversion rates dropped to
> below half of what they usually are, which was an obvious consequence of
> our servers randomly locking up. Plus, it was very easy to reproduce the
> deadlocks, which seemed to "magically unlock" when opening a second
> tab/window and opening the same URL that was locked on the other
> window/tab. Doing this unlocked both windows/tabs at once, immediately.
>
> We found this was only happening on HTTPS, but NOT on HTTP. Furthermore,
> we found this was only happening when the browser negotiated an upgrade to
> HTTPS/2.0
> Once we found this, we temporarily removed the className="org.apache.coyote.http2.Http2Protocol" /> configuration, and all
> was back to normal.
> However, we need HTTP/2, so we continued to look for a proper solution.
>
> Looking at the Tomcat changelog, we found there have been many changes
> since 9.0.17 related to useAsyncIO and HTTP/2. One particular change for
> 9.0.22 caught our attention:
>
>
> *"Remove a source of potential deadlocks when using HTTP/2 when the
> Connector is configured with useAsyncIO as true. (markt)" *We also found
> the following discussion thread, which describes issues similar to what we
> were experiencing:
>
> http://mail-archives.apache.org/mod_mbox/tomcat-dev/201906.mbox/%3c20190606204631.bab6c8a...@gitbox.apache.org%3e
>
> So we upgraded to 9.0.22 thinking that the deadlock would be gone. But
> alas, it was not. The deadlocks remained.
> We found that 9.0.20 changed the default for useAsyncIO from "false" to
> "true". So we changed useAsyncIO back to what it was when we were running
> 9.0.17 (false) and all is back to normal on 9.0.22
>
> So the conclusion is: there are still deadlock bugs on the NIO connector
> with useAsyncIO="true" and upgrades to HTTP/2.0
> Besides fixing them, we believe that the useAsyncIO default should be
> reverted to "false".
>
> We could find no Java deadlocked threads at all by inspecting jconsole
> (not with the automatic "find deadlocks" functionality, nor by inspection
> of a thread dump). We performed several thread dumps WHILE the deadlock was
> clearly visible on screen (this was very easily reproduceable).
>
> The deadlock is definitely there though and goes away as soon as we turn
> off "useAsyncIO".
> Since we could not find Java-level deadlocks, we believe the problem
> probably lies in the interaction with native code.
> We are using org.apache.catalina.core.AprLifecycleListener as well as
> Tomcat Native 1.2.23 on Linux.
> We could not find any pointers in the Tomcat Native changelog dealing with
> similar issues.
>
> Any ideas? Thanks,
>
To investigate your problem, we would need to have an idea on how to
reproduce it.
If you want to debug it yourself, you can turn on the debug logging in
conf/logging.properties:
org.apache.coyote.http2.level = FINE
It's very verbose though.
Rémy
