Sure looks like a potential threading problem. Beyond that, I can't
say much unfortunately as I, like most everyone else on the planet, used to
assume Double Check locks were thread safe.
--- Pat
PS Now they tell me x++ isn't thread safe either and I need to use
AtomicInteger.incrementAndGet() instead. The JVM designers need to make up
their minds :).
> -----Original Message-----
> From: Michael Prescott [mailto:[EMAIL PROTECTED]
> Sent: Wednesday, December 14, 2005 2:02 PM
> To: [email protected]
> Subject: 3.0.3: Double-checked locking on enhancement
>
> We're coming across an unusual exception that occurs when our
> application is under load. Below is an example stack trace, although
> the problem can occur while enhancing any of a number of things, so it
> doesn't seem specific to one part of our application. The root
> exception is always the same, however:
>
> javassist.CannotCompileException: duplicate method: <init>
>
> Since it seemed to be related to concurrency, we were reading through
> the Tapestry classes along this stack, and found what looks like a
> threading problem in DefaultComponentClassEnhancer.java:
>
> public Class getEnhancedClass(IComponentSpecification specification,
> String className)
> {
> Class result = getCachedClass(specification);
>
> if (result == null)
> {
> synchronized (this)
> {
> result = getCachedClass(specification);
> if (result == null)
> {
> result = constructComponentClass(specification,
> className);
> storeCachedClass(specification, result);
> }
> }
> }
>
> return result;
> }
>
> This is double-checked locking, which isn't safe given instruction
> reordering and thread-specific copies of variables, and all that
> multi-CPU magic. This problem is occurring on an 8-CPU server, which
> I'm guessing is enough processors to expose the subtle ways in which
> double-checked locking can fail.
>
> Does this ring any bells for anyone? I realize this is a somewhat
> nebulous query.
>
> Michael
>
> org.apache.tapestry.ApplicationRuntimeException: A code generation error
> occured while enhancing class org.apache.tapestry.link.GenericLink.
> at
> org.apache.tapestry.enhance.DefaultComponentClassEnhancer.constructCompo
> nentClass(DefaultComponentClassEnhancer.java:151)
> at
> org.apache.tapestry.enhance.DefaultComponentClassEnhancer.getEnhancedCla
> ss(DefaultComponentClassEnhancer.java:97)
> at
> org.apache.tapestry.pageload.PageLoader.instantiateComponent(PageLoader.
> java:603)
> at
> org.apache.tapestry.pageload.PageLoader.createImplicitComponent(PageLoad
> er.java:569)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.createImplicitComponent(
> BaseComponentTemplateLoader.java:295)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:237)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:172)
> at
> org.apache.tapestry.BaseComponent.readTemplate(BaseComponent.java:100)
> at
> org.apache.tapestry.BaseComponent.finishLoad(BaseComponent.java:135)
> at
> org.apache.tapestry.pageload.PageLoader.constructComponent(PageLoader.ja
> va:519)
> at
> org.apache.tapestry.pageload.PageLoader.createImplicitComponent(PageLoad
> er.java:576)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.createImplicitComponent(
> BaseComponentTemplateLoader.java:295)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:237)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:172)
> at
> org.apache.tapestry.BaseComponent.readTemplate(BaseComponent.java:100)
> at
> org.apache.tapestry.BaseComponent.finishLoad(BaseComponent.java:135)
> at
> org.apache.tapestry.pageload.PageLoader.constructComponent(PageLoader.ja
> va:519)
> at
> org.apache.tapestry.pageload.PageLoader.createImplicitComponent(PageLoad
> er.java:576)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.createImplicitComponent(
> BaseComponentTemplateLoader.java:295)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:237)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:172)
> at
> org.apache.tapestry.BaseComponent.readTemplate(BaseComponent.java:100)
> at
> org.apache.tapestry.BaseComponent.finishLoad(BaseComponent.java:135)
> at
> org.apache.tapestry.pageload.PageLoader.constructComponent(PageLoader.ja
> va:519)
> at
> org.apache.tapestry.pageload.PageLoader.createImplicitComponent(PageLoad
> er.java:576)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.createImplicitComponent(
> BaseComponentTemplateLoader.java:295)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:237)
> at
> org.apache.tapestry.BaseComponentTemplateLoader.process(BaseComponentTem
> plateLoader.java:172)
> at
> org.apache.tapestry.BaseComponent.readTemplate(BaseComponent.java:100)
> at
> org.apache.tapestry.BaseComponent.finishLoad(BaseComponent.java:135)
> at
> org.apache.tapestry.pageload.PageLoader.constructComponent(PageLoader.ja
> va:519)
> at
> org.apache.tapestry.pageload.PageLoader.loadPage(PageLoader.java:764)
> at
> org.apache.tapestry.pageload.PageSource.getPage(PageSource.java:152)
> at
> org.apache.tapestry.engine.RequestCycle.getPage(RequestCycle.java:195)
> at
> org.apache.tapestry.engine.ActionService.service(ActionService.java:125)
> at
> org.apache.tapestry.engine.AbstractEngine.service(AbstractEngine.java:88
> 9)
> at
> org.apache.tapestry.ApplicationServlet.doService(ApplicationServlet.java
> :198)
> at
> net.exchangesolutions.sn.ui.tapestry.SynchronizedServlet.doService(Synch
> ronizedServlet.java:37)
> at
> org.apache.tapestry.ApplicationServlet.doGet(ApplicationServlet.java:159
> )
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:115)
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:92)
> at
> com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChai
> n.java:99)
> at
> net.exchangesolutions.sncore.servlet.StateFilter.doFilter(StateFilter.ja
> va:56)
> at
> com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.
> java:70)
> at
> com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.ja
> va:163)
> at
> com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.j
> ava:208)
> at
> com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:396)
> at
> com.caucho.server.port.TcpConnection.run(TcpConnection.java:363)
> at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:490)
> at com.caucho.util.ThreadPool.run(ThreadPool.java:423)
> at java.lang.Thread.run(Thread.java:595)
> Caused by: org.apache.tapestry.enhance.CodeGenerationException
> at
> org.apache.tapestry.enhance.javassist.ClassFabricator.getByteCode(ClassF
> abricator.java:291)
> at
> org.apache.tapestry.enhance.javassist.EnhancedClass.createEnhancedSubcla
> ss(EnhancedClass.java:130)
> at
> org.apache.tapestry.enhance.ComponentClassFactory.createEnhancedSubclass
> (ComponentClassFactory.java:336)
> at
> org.apache.tapestry.enhance.DefaultComponentClassEnhancer.constructCompo
> nentClass(DefaultComponentClassEnhancer.java:143)
> ... 50 more
> Caused by: javassist.CannotCompileException: duplicate method: <init>
> at
> javassist.bytecode.ClassFile.testExistingMethod(ClassFile.java:488)
> at javassist.bytecode.ClassFile.addMethod(ClassFile.java:472)
> at javassist.CtClassType.addConstructor(CtClassType.java:885)
> at javassist.CtNewClass.addConstructor(CtNewClass.java:55)
> at
> javassist.CtNewClass.inheritAllConstructors(CtNewClass.java:96)
> at javassist.CtNewClass.toBytecode(CtNewClass.java:63)
> at javassist.CtClass.toBytecode(CtClass.java:1021)
> at
> org.apache.tapestry.enhance.javassist.ClassFabricator.getByteCode(ClassF
> abricator.java:279)
> ... 53 more
>
>
> Michael Prescott
> direct: 416.646.7062
>
> main: 416.646.7000
> fax: 416.646.7050
>
> Exchange Solutions Inc.
> 250 Yonge Street, 18th Floor
> Toronto, ON M5B 2L7
> www.exchangesolutions.com
>
>
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