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From Geeth Munasinghe <geeth...@gmail.com>
Subject [Axiom] Encountered OOM issue when service.xml has ServiceTCCL parameter.
Date Wed, 17 Sep 2014 16:25:52 GMT
Hi all,

We are using axis2-1.6.1 version, it uses axiom 1.2.11 version, We recently
encountered a OOM problem with two services which uses ServiceTCCL
parameter. We are using this parameter because both those services use
spring and hibernate with them. Scenario is one service is calling the
other service. So one service acts as the client.

We analyzed the heap dumps and found out that OOM issue was caused by
org.apache.axiom.om.util.
StAXUtils class. There are few weakhashmaps used in that class. Two of them
are

   1. inputFactoryPerCLMap
   2. outputFactoryPerCLMap

And those two weak hashmaps has other weak hashmaps inside of them. Those
inner hashmaps cause the issue.

We found out that when we use ServiceTCCL parameter  in the service.xml, in
AbstractMessageReceiver.java  [1] of axis2 (line number 152 - 170) creates
a new class loader object of the MultiParentClassLoader [2] for every
request. So in StAXUtils class [3] in axiom, methods [4] and [5] uses
inner  weak hashmaps of inputFactoryPerCLMap,  outputFactoryPerCLMap and
fill them with the class loader as the key and XMLInputFactory /
XMLOutputFactory as the value.

Because every request gets a new class loader object of the
MultiParentClassLoader, their hash values are different. So they are keep
getting filled into those inner weak hash maps. Because the same key
(classloder instance) gets inserted into both weak hashmaps, garbage
collector does not remove them. So server goes OOM, When we analyze the
heap dumps we found out that java.util.WeakHashMap fills over 80% of the
memory when it goes OOM.

I have made fix in StAXUtils in axiom as follows.

Instead map.get(cl) I change it to map.get(cl.getClass().getName())

Instead map.put(cl, factory) I changed it to
map.put(cl.getClass().getName(), factory)

I have attached the fix (svn diff) here with email. I am not sure I have
done the correct fix for the issue. But I found that it solves my problem.
Can some one please verify weather I have done the correct fix.

Please consider that upgrading to new axis2 is not a solution for us at the
moment.

[1]
http://svn.apache.org/repos/asf/axis/axis2/java/core/tags/v1.6.1/modules/kernel/src/org/apache/axis2/receivers/AbstractMessageReceiver.java

[2] org.apache.axis2.classloader.MultiParentClassLoader

[3] org.apache.axiom.om.util.StAXUtils

[4] getXMLInputFactory_perClassLoader(StAXParserConfiguration configuration)

[5] getXMLOutputFactory_perClassLoader(StAXWriterConfiguration
configuration)


Thanks in advance.

Geeth

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