Concurrent Access to a File

[ebell]

So, I'm in a situation where I have a workflow that assigns a task to a group of pooled users.  What I'm having happening is that User A opens the document about the same time User B opens the document.  User A takes ownership and continues to evaluate the document, while User B does the same in his browser.  Then, User A decides the content is good and clicks on approve.  Meanwhile, User B still has a copy of the content open.  Eventually, User B decides he approves or rejects the content and when he does, he triggers an exception, because the workflow has already progressed past that point. 

Does anyone have some ideas on how I could resolve this? 

For reference, here's the error I'm getting…

2008-06-19 16:02:33,049 INFO  [STDOUT] 16:02:33,045 User:corporate ERROR [ui.common.Utils] A system error happened during the operation: Transition 'approve' is invalid for Workflow task 'jbpm$326'
org.alfresco.service.cmr.workflow.WorkflowException: Transition 'approve' is invalid for Workflow task 'jbpm$326'
   at org.alfresco.repo.workflow.jbpm.JBPMEngine$26.doInJbpm(JBPMEngine.java:1679)
   at org.springmodules.workflow.jbpm31.JbpmTemplate$1.doInHibernate(JbpmTemplate.java:87)
   at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:367)
   at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:333)
   at org.springmodules.workflow.jbpm31.JbpmTemplate.execute(JbpmTemplate.java:80)
   at org.alfresco.repo.workflow.jbpm.JBPMEngine.endTask(JBPMEngine.java:1649)
   at org.alfresco.repo.workflow.WorkflowServiceImpl.endTask(WorkflowServiceImpl.java:488)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:281)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:187)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:154)
   at org.alfresco.repo.security.permissions.impl.AlwaysProceedMethodInterceptor.invoke(AlwaysProceedMethodInterceptor.java:40)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
   at org.alfresco.repo.security.permissions.impl.ExceptionTranslatorMethodInterceptor.invoke(ExceptionTranslatorMethodInterceptor.java:49)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
   at org.alfresco.repo.audit.AuditComponentImpl.audit(AuditComponentImpl.java:241)
   at org.alfresco.repo.audit.AuditMethodInterceptor.invoke(AuditMethodInterceptor.java:69)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
   at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:107)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176)
   at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:210)
   at $Proxy100.endTask(Unknown Source)
   at org.alfresco.web.bean.workflow.ManageTaskDialog.transition(ManageTaskDialog.java:393)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at org.apache.myfaces.el.MethodBindingImpl.invoke(MethodBindingImpl.java:132)
   at org.apache.myfaces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:61)
   at javax.faces.component.UICommand.broadcast(UICommand.java:109)
   at javax.faces.component.UIViewRoot._broadcastForPhase(UIViewRoot.java:97)
   at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:171)
   at org.apache.myfaces.lifecycle.InvokeApplicationExecutor.execute(InvokeApplicationExecutor.java:32)
   at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:95)
   at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:70)
   at javax.faces.webapp.FacesServlet.service(FacesServlet.java:139)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   at org.alfresco.web.app.servlet.AuthenticationFilter.doFilter(AuthenticationFilter.java:81)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
   at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
   at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
   at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
   at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
   at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
   at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
   at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
   at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
   at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
   at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
   at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
   at java.lang.Thread.run(Thread.java:619)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[ebell]

I know that in Alfresco, there's an ability to checkout content.  But, as a workflow is not a type of content, I don't see the ability to checkout a workflow.  The take ownership button prevents the likelihood that an error from concurrently modifying the same workflow task would occur.  However, in the situation I described, this chance still exists. 
I've thought of a possible setup that may solve the problem… essentially, as soon as a task is selected, I want to assign it to the person who viewed the task.  (As if the person who opened the task is unable to approve a document, he or she can always return the task to the pool, permitting another user to look at the task) 
Any ideas?