1 Reply Latest reply on Aug 28, 2002 6:58 AM by manan

concurrent modification problem: java.util.ConcurrentModific

manan Aug 28, 2002 4:42 AM

1. Taskmanager is the servlet class I am using. No code written related to "threads" is being written. I encountered this exception "java.util.ConcurrentModificationException"

This exception may be thrown by methods that have detected concurrent modification of a backing object when such modification is not permissible. For some reasons, two thread are getting started.

I am encountering the following error:

StandardWrapperValve[taskmanager]: Servlet.service()
for servlet taskmanager threw exception java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.next(HashMap.java:736)
at org.apache.catalina.util.Enumerator.nextElement(Enumerator.java:166)
at TaskManager.doPost(TaskManager.java:139)
at TaskManager.doGet(TaskManager.java:54)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperV
alve.java:243)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav
a:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextV
alve.java:190)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:566)
at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve
.java:246)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav
a:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)

at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:
2343)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.j
ava:180)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:566)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatche
rValve.java:170)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:564)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.j
ava:170)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:564)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:
468)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav
a:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineVal
ve.java:174)
at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline
.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.jav
a:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)

at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcesso
r.java:1012)
at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.ja
va:1107)
at java.lang.Thread.run(Thread.java:484)

For some reasons, it seems that a new thread is getting started.

Do I need to specify in some file that no new thread should start-off. How can I get rid of this error?

Any pointers?

1. Re: concurrent modification problem: java.util.ConcurrentMod

manan Aug 28, 2002 6:58 AM (in response to manan)

Relevant Code present for session tracking is:

String enumName = "";
while(sessionNames.hasMoreElements())
{
enumName = (String)sessionNames.nextElement();
session.removeAttribute(enumName);
}

When I uncomment the above code and run my application, it works fine.

Since I need to setattribute also, therefore ,I dont want to use session.invalidate().

Right now ,what it seems different threads get created if I dont comment the code.

How can I run the application without commenting above code on jboss-3.0.0_tomcat-4.0.3?

any pointers?
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