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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Installing APR based Apache Tomcat Native Library
Date Wed, 03 Feb 2016 15:02:48 GMT
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Yuval,

On 2/2/16 6:11 PM, Yuval Schwartz wrote:
> Thanks. Answers below
> 
> On Tuesday, 2 February 2016, Christopher Schultz < 
> chris@christopherschultz.net 
> <javascript:_e(%7B%7D,'cvml','chris@christopherschultz.net');>>
> wrote:
> 
> Yuval,
> 
> On 2/2/16 9:28 AM, Yuval Schwartz wrote:
>>>> On Tue, Feb 2, 2016 at 4:15 PM, Christopher Schultz < 
>>>> chris@christopherschultz.net> wrote:
>>>> 
>>>> Yuval,
>>>> 
>>>> On 2/2/16 6:21 AM, Yuval Schwartz wrote:
>>>>>>> Hello again Christoph,
>>>>>>> 
>>>>>>> I think there is a problem with the way that I
>>>>>>> installed the APR library. If you recall, I installed a
>>>>>>> compiled version from the distros with the commands yum
>>>>>>> install apr-devel openssl-devel tomcat-native
>>>>>>> 
>>>>>>> I get the desired "Loaded APR based library" in my
>>>>>>> logs. However, every time I shut down tomcat I get a
>>>>>>> warning:
>>>>>>> 
>>>>>>> WARNING [main] 
>>>>>>> org.apache.tomcat.util.net.AbstractEndpoint.shutdownExecutor
>>>>>>>
>>>>>>> 
The executor associated with thread pool [http-apr-8080] has
>>>>>>> not fully shutdown. Some application threads may still
>>>>>>> be running
>>>>>>> 
>>>>>>> If I remove the packages that I installed (yum remove 
>>>>>>> apr-devel openssl-devel tomcat-native) then this
>>>>>>> warning goes away.
>>>>>>> 
>>>>>>> Is there something that I forgot to configure when
>>>>>>> installing the APR library?
>>>> 
>>>> What makes you think that something is wrong with the
>>>> library? Perhaps you are getting that WARNING because you
>>>> have still-running request-processing threads?
>>>> 
>>>> 
>>>>> Thanks, any ideas on how I can look into this then? I've
>>>>> tried looking at thread dumps and at the threads that are
>>>>> created and destroyed in my ServletContextListener's
>>>>> contextInitialize and contextDestroyed methods.
> 
> So, just to confirm, when you attempt to shut-down Tomcat, you get 
> that WARNING and if you take a thread dump after that warning, you 
> have threads still running contextInitialized and
> contextDestroyed?
> 
> 
>> When I shut down I get that message (I am able to shut down
>> successfully, I just get that message right before). I can't take
>> a thread dump after I get the message because tomcat is no longer
>> running (i.e. There are no Java processes taking place for me to 
>> perform a thread dump on).

Try this. Before you are ready to shut down, take note of the pid of
the JVM process. Then run this command:

$ CATALINA_HOME/bin/shutdown.sh && sleep 2 && jstack [pid] > stack.txt

This should request a Tomcat shutdown and take a thread dump 2 seconds
later. If that doesn't work, adjust the sleep time until you get a
good snapshot. You should see a thread with a name like
http-apr-8080-[#] that is doing something inside your application.
then its up to you to figure out why it's still running.

>> I mentioned contextInitialized and contextDestroyed simply
>> because I used those methods to print information about threads
>> that were running in order to try to get a better idea of what's
>> going on (i.e. Using Thread.getAllStackTraces()).

Well, if you are using contextInitialized and contextDestroyed to dump
the stacks of all threads, then of course those methods will be listed
- -- they are currently running (to generate the thread dumps).

> The thread the WARNING is talking about will be one of the HTTP 
> request processor threads (it even tells you which thread pool is 
> still in use: http-apr-8080). If you have some long-running
> requests, you may get that WARNING during shutdown, but shutdown
> can still succeed after those threads complete.
> 
> 
>> When I take a thread dump while the application is running I see
>> threads called http-apr-8080-exec-1, http-apr-8080-exec-2, etc.
>> do these threads belong to the pool that the warning is referring
>> to?

Yes, but while the server is running, you should be expecting to
handle requests from clients, right? The fact that those threads are
running is not out of the ordinary. Remember that even threads not
actively servicing requests will have a non-null stack trace: they'll
be waiting for new requests.

>> Are you saying I don't need to pay attention to this warning? As
>> a side question: why should it concern me that a thread might
>> stay open when tomcat is shutting down? If tomcat is shutting
>> down then won't all threads be destroyed anyway?

If a request is in-progress when you ask Tomcat to shut down, Tomcat
will wait for a certain amount of time for those requests to complete.
If they don't complete within a certain amount of time (configurable:
see the Configuration section of the user's guide), Tomcat will stop
them anyway and shut down.

If you get this error every time you shut down, you should find out
which thread is running long and figure out why.

>>>> If the library loads, I think you installed it properly ;)
>>>> 
>>>> 
>>>>> Yes, I just reinstalled by compiling the source code and I
>>>>> still get the same error...so it's not the library.
> 
> If you are okay with the library version available from your Linux 
> distro, you should stick with that.
> 
>> I mentioned this point because, interestingly, when I don't use
>> the apr library (i.e. I use the standard nio) then I don't see
>> the warning that we're discussing.

So if you use the BIO connector, you never get this warning?

What is your connector configuration?

- -chris
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