ThreadWithAttributes possible leak

[clebert.suconic]

On this JIRA:

http://jira.jboss.org/jira/browse/JBAS-3074


I have done some research on memory leaks on redeployments for WebServices.

The biggest part of the leakage is already found (look at the JIRA), but there still an issue with ThreadWithAttributes on Tomcat.

I'm not sure how the Class/ClassLoader got set into ThreadWithAttributes, but is it possible to clear it before the Thread goes back to the pool (to sleep).

It's going to be hard to create testcases if we don't clear those variables when these threads are in sleep state.


My idea was to patch ThreadWithAttributes, or make sure that Tomcat is clearing its litter before the Threads goes back to the pool.

In case we decide by the patch, here is my proposal:

public class ThreadWithAttributes extends Thread {
 .....

 class WraperWeak
 {
 public WrapperWeak(Object obj)
 {
 ref=new WeakReference(obj);
 }
 public Object get()
 {
 return ref.get();
 }
 WeakReference ref;
 }

 private HashMap attributes=new HashMap() // Why this needs to be a HashTable if this is a thread-local like structure?
 {
 public void put(Object key, Object value)
 {
 if (value instanceof Class || value instanceof ClassLoader)
 {
 value = new WrapperWeak(value);
 }
 super.put(key,value);
 }
 public void get(Object key)
 {
 value = super.get(key);
 if (value instanceof WrapperWeak)
 {
 return ((WrapperWeak)value).get();
 } else
 {
 return value;
 }
 }
 }

 .....

Any ideas?

[starksm64]

Need to get Remy to comment on how this can be cleaned up.

[clebert.suconic]

This is not a production leakage.

As soon as the Thread is used to some other application, the reference is gone.

This is an issue when running testcases trying to chase leaks.

[clebert.suconic]

Besides, clearing these references wouldn't affect performance either.

[rmaucher]

The attributes hashtable is not called or used anywhere (it is a Tomcat 3.x artifact). As a result, it cannot cause any memory leaks.

[clebert.suconic]

Ok... I kind of agree with attributes on that class.

But where the object Class get referenced within ThreadWithAttributes? I'm clearing seeing references there.

Anywhere in Tomcat, or this could be caused by WebService's code?

[rmaucher]

The reference trace seems to mention ThreadLocals. ThreadWithAttributes extends thread, and doesn't add much, although the version of Tomcat that is used in JBoss still uses the thData object array.