Memory leak exception

Question

can anyone help me with this exception :

Jul 23, 2012 11:00:57 AM org.apache.catalina.loader.WebappClassLoader loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load com.mchange.v2.sql.SqlUtils.  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.
java.lang.IllegalStateException
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1597)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1556)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:531)
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
    at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:78)
    at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
    at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
    at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
    at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
    at net.customware.gwt.dispatch.server.AbstractDispatch.doExecute(AbstractDispatch.java:81)
    at net.customware.gwt.dispatch.server.AbstractDispatch.execute(AbstractDispatch.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:569)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at com.google.inject.servlet.ServletDefinition.doService(ServletDefinition.java:216)
    at com.google.inject.servlet.ServletDefinition.service(ServletDefinition.java:141)
    at com.google.inject.servlet.ManagedServletPipeline.service(ManagedServletPipeline.java:93)
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:63)
    at com.google.inject.servlet.ManagedFilterPipeline.dispatch(ManagedFilterPipeline.java:122)
    at com.google.inject.servlet.GuiceFilter.doFilter(GuiceFilter.java:110)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

And also provide the possible solution for it..?

Thanks in advance...

Answer 1

the basic issue is that tomcat creates a new ClassLoader for each webapp and disables the classloader when you reset the app, e.g. by hot deploying a new version. c3p0 creates helper threads. if c3p0 has been loaded within the web app's class loader and then the app is reset, c3p0's threads may still be live and hold references to objects loaded from the now defunct ClassLoader, leading to the kind of error you see when a new Class must be loaded.

interactions between multithreaded components and tomcat's "hot" ClassLoading scheme can be challenging. some suggestions:

1) if your web app constructs its own c3p0 DataSource (for example in an ContextListener), be sure that the DataSource is also close()ed when the app is shut down (in the same ContextListener)

2) try to have c3p0 and your JDBC driver classes loaded in something other than the web-app specific ClassLoader. put the c3p0 jar file, the change-commons-java jar file, and your JDBC driver jar file where either the common, system, or bootstrap ClassLoader will find it. Be sure to take these files out out your webapp's lib directory, because the web app ClassLoader is tried first. See http://tomcat.apache.org/tomcat-6.0-doc/class-loader-howto.html for more.

I hope this helps!