Dear Madame or Sir
we are facing some serious performance issues, caused by the
implementation of the "org.apache.xerces.impl.dv.DTDDVFactory" and the
"org.apache.xerces.impl.dv.ObjectFactory" classes.
Our environment is based on Oracle WebLogic server 10.3.2, Sun JDK
160_16 and Xerces 2.8.1
Basically what we see is an high number of threads blocked by the method
getInstance of the "org.apache.xerces.impl.dv.DTDDVFactory" class.
An example is given here:
---------------------------------- THREAD DUMP START
---------------------------------------------
"[ACTIVE] ExecuteThread: '99' for queue: 'weblogic.kernel.Default
(self-tuning)'" daemon prio=6 tid=0x08597400 nid=0x1444 waiting for
monitor entry [0x4143e000]
java.lang.Thread.State: BLOCKED (on object monitor)
at org.apache.xerces.impl.dv.DTDDVFactory.getInstance(Unknown
Source)
- waiting to lock <0x2a008228> (a java.lang.Class for
org.apache.xerces.impl.dv.DTDDVFactory)
at org.apache.xerces.parsers.XML11Configuration.<init>(Unknown
Source)
at
org.apache.xerces.parsers.XIncludeAwareParserConfiguration.<init>(Unknow
n Source)
at
org.apache.xerces.parsers.XMLGrammarCachingConfiguration.<init>(Unknown
Source)
at
org.apache.xerces.parsers.XMLGrammarCachingConfiguration.<init>(Unknown
Source)
at
sun.reflect.GeneratedConstructorAccessor61.newInstance(Unknown Source)
at
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingCons
tructorAccessorImpl.java:27)
at
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:355)
at java.lang.Class.newInstance(Class.java:308)
at org.apache.xerces.parsers.ObjectFactory.newInstance(Unknown
Source)
at org.apache.xerces.parsers.ObjectFactory.createObject(Unknown
Source)
at org.apache.xerces.parsers.ObjectFactory.createObject(Unknown
Source)
at org.apache.xerces.parsers.DOMParser.<init>(Unknown Source)
at org.apache.xerces.parsers.DOMParser.<init>(Unknown Source)
at org.apache.xerces.jaxp.DocumentBuilderImpl.<init>(Unknown
Source)
at
org.apache.xerces.jaxp.DocumentBuilderFactoryImpl.newDocumentBuilder(Unk
nown Source)
---------------------------------- THREAD DUMP END
---------------------------------------------
Out of 100 threads available 72 are blocked there when the server is
under stress.
To understand the issue, is useful to remember that when a Class.forName
is done (like the ObjectFactory class invoked from the DTDDVFactory
does) it can takes (depending from the dimension of the classpath) up to
2-4 seconds which is a huge time if this is invoked continuosly.
Our suggestion would be to cache the class objects per ClassLoader in
the DTDDVFactory, at least for the default implementation
("org.apache.xerces.impl.dv.dtd.DTDDVFactoryImpl") so that the search of
this class object in the context of a ClassLoader is done only once. If
there is any concern about backward compatibility this could be done
only if a specific System Property is set, which would enable the
feature and/or configure the size of this (LRU) cache.
A similar issue (but less heavy in performance) can be found in the
TransformerFactory.
Would such a change be possible?
Gladly awaiting your answer and feedback.
Kind regards
Carlo de Rossi
