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How to stop threads created by org.asynchttpclient to prevent memory leak?

I am using org.asynchttpclient to post async request.
While shutting down tomcat, I am getting below logs:
SEVERE: The web application [/test] appears to have started a thread named [pool-1-thread-1] but has failed to stop it. This is very likely to create a memory leak.
Jul 04, 2017 10:53:00 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/test] appears to have started a thread named [AsyncHttpClient-2-1] but has failed to stop it. This is very likely to create a memory leak.
Jul 04, 2017 10:53:00 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/test] appears to have started a thread named [AsyncHttpClient-2-2] but has failed to stop it. This is very likely to create a memory leak.
Jul 04, 2017 10:53:00 AM org.apache.catalina.loader.WebappClassLoaderBase checkThreadLocalMapForLeaks
SEVERE: The web application [/test] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal#71513074]) and a value of type [io.netty.util.internal.InternalThreadLocalMap] (value [io.netty.util.internal.InternalThreadLocalMap#4aecc2e8]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
How to close these threads to prevent memory leak.

This is really more of a warning and in most times can be ignored. You will see this error when the context is reloaded or shut down. If you are shutting down the server then the JVM will be shutdown also and the os will clean up any memory.
If you want to try and call close on the AsyncHttpClient which implements Closable it may stop this issue. You will probably have to put a wait in there to let it fully close the connection factory. You can look at the tomcat Lifecycle to add a shutdown handler to handle closing the client.

Tomcat crashes while access large database table

When my database request takes too long tomcat crashes / closes and I find this in my log. I am totally clueless right now :)
Any thoughts ?
SEVERE: The web application [/ir] is still processing a request that
has yet to finish. This is very likely to create a memory leak. You
can control the time allowed for requests to finish by using the
unloadDelay attribute of the standard Context implementation.
Mar 14, 2015 2:14:38 AM org.apache.catalina.loader.WebappClassLoader
clearReferencesThreads
SEVERE: The web application [/ir] appears to have started a thread
named [MySQL Statement Cancellation Timer] but has failed to stop it.
This is very likely to create a memory leak.
What should I be doing ?

Does ojdbc still use CharacterConverter002e.glb?

In my web-based application, we've recently implemented language (utf-8) support. Since we have gotten it working, I have had the following error message spammed in my tomcat output. I don't have to have the web page open, only the application deployed, and this starts printing to the output at exact 30 second intervals, 5 times per interval.
Oct 09, 2013 4:26:46 PM org.apache.catalina.loader.WebappClassLoader findResourceInternal
INFO: Illegal access: this web application instance has been stopped already.
Could not load oracle/sql/converter_xcharset/CharacterConverter002e.glb. The
eventual following stack trace is caused by an error thrown for debugging purposes
as well as to attempt to terminate the thread which caused the illegal access, and
has no functional impact.
I am using ojdbc6 and see that there isn't anything like "CharacterConverter002e.glb" in the library. What is causing my application to look for this? Am I using the wrong ojdbc? It doesn't appear to keep anything from working but it's bothersome.

Tomcat memory leak - Stopping Guava Finalizer thread

I have a Spring web application running on Tomcat.
When trying to shutdown Tomcat with the shutdown.sh script, the java process doesn't end because it has a Thread that's still running. The catalina.log contains
Jul 22, 2013 2:07:50 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/myapp] appears to have started a thread named [com.google.common.base.internal.Finalizer] but has failed to stop it. This is very likely to create a memory leak.
Apparently BoneCP has some Guava integration that causes this thread to block. Is there a clean or intended way to kill this thread?

There's an open issue on Guava for this problem - the issue itself is pretty old but if you check the latest comments you'll see some suggestions from other BoneCP users to resolve this issue
Also check this other issue and this patch

Tomcat 6 memory leaks log entries

Below is outtake of unique entries in my Catalina.out file on CentOS machine. I'm running Tomcat 6 with spring 3 and my application. There is whole bunch of them so I just picked some that keep repeating. This doesn't happen all the time but it happens at least once a week.
The Question is what can I do to prevent the bellow from happening?
Feb 3, 2011 2:37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
SEVERE: The web application [] registered the JBDC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
Feb 3, 2011 2:37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [] appears to have started a thread named [com.iteezy.shared.domain.DirEntry.data] but has failed to stop it. This is very likely to create a memory leak.
Feb 3, 2011 2:37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [] appears to have started a thread named
[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] but has failed to stop it. This is very likely to create a memory leak.
Feb 3, 2011 2:37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [] appears to have started a thread named [File Reaper] but has failed to stop it. This is very likely to create a memory leak.
Feb 3, 2011 2:37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [] appears to have started a thread named [pool-1-thread-22] but has failed to stop it. This is very likely to create a memory leak.
37:48 PM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
b application [] appears to have started a thread named
[org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-2] but has failed to stop it. This is very likely to create a memory leak.
37:48 PM org.apache.catalina.loader.WebappClassLoader clearThreadLocalMap
b application [] created a ThreadLocal with key of type [net.sf.json.AbstractJSON$1] (value [net.sf.json.AbstractJSON$1#40bbb3d6]) and a value of type [java.util.HashSet] (value [[]]) but failed to remove it when the web application was stopped. This is very likely to create a memory leak.

When you define an external flag which a thread is suppose to poll and exit when it's set - it must be volatile. Otherwise the thread might never see the change made by other thread.
However there is already a feature like that in standard API - it is called an interrupt() method and Thread.currentThread().isInterrupted(). No need to duplicate already existing logic. See: Stopping a specific java thread.
That being said calling interrupt() on each and every thread is a bad idea as well because there is no guarantee that all threads respond to it. Examining your exceptions I noticed the following threads not being cleaned up properly:
com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0 - close the C3P0 data source. Since you are using Spring simply add destroy-method="close". We're done with this thread.
File Reaper - as far as I can see this thread is created by FileCleaningTracker. You need to call FileCleaningTracker.exitWhenFinished() explicitly when shutting down your application (or when the class is no longer needed, I never used it) or let Spring to do this (see above). Chances are some 3rd party library uses it and not closing properly - this means it has a bug.
pool-1-thread-22 - this is one of the threads created by Executors utility inside ExecutorService. Make sure you call shutdown() on every such a pool in your application during shutdown.
org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-2 - Quartz worker thread (the one that actually runs jobs). SchedulerFactoryBean closes the scheduler for you automatically, I think Tomcat is mistaken here, I see this error often as well. Nevertheless looks like setting SchedulerFactoryBean.waitForJobsToCompleteOnShutdown to true solves this.
com.iteezy.shared.domain.DirEntry.data - I am not sure about this one. It is either your own thread that needs to be interrupted upon shutdown or H2 database thread (?) Its stack needs to be examined to guess where does it come from.
The bottom line is: don't just kill everything that moves (actually, Tomcat does that for you after issuing this warning) but determine where the threads come from and use framework/library specific close() method to allow further cleanup. Be gentle.

Set up a Servlet to manage this in its destroy() method. The threads can check a flag to see if they must continue or not.
In your servlet, do the following in the destroy method. You will obviously need to be able to have access to a Collection<MyThread> but how you get that really depends on how your system is set up.
destroy() {
for (MyThread thread : myThreads) {
thread.stopProcessing();
}
}
Your MyThread class will have something like this:
public class MyThread {
private boolean finished = false;
#Override
public void run() {
while (!finished) {
//do something
}
}
public void stopProcessing() {
finished = true;
}
}

Shutdown your webapp properly. Don't leave these threads running.
Alternatively, don't keep redeploying the webapp.