Yeah, unfortunately this is a known problem that we need to solve: https://issues.apache.org/jira/browse/CAY-957
It was partially fixed in Cayenne 3.1: https://issues.apache.org/jira/browse/CAY-1653 But there's still a condition when that can happen. As a workaround you can create nested contexts that are subclasses of DataContext, overriding 'setChannel' (3.0.x) or 'attachToChannel' (3.1.x) to suppress this line: EventUtil.listenForChannelEvents(channel, mergeHandler); This way peer nested context events won't get propagated, and the deadlock should not occur. Andrus On Sep 6, 2012, at 7:16 PM, Ramiro Aparicio wrote: > Hi, > > I have been debugging some strange errors in our web app that seems to be > related to context and threads, let me explain, we are using Cayenne 3.0.1 > using WebApplicationContextFilter to bind the context to threads, in some > parts of the application is not so difficult to be processing several AJAX > request from the same user, and they go to different threads but using the > same context (because of the context per session setup) and this causes race > condition errors from time to time. > To avoid that I have switched to use nested context per request, this allows > us to use the filter as ever but avoid messing contexts in different threads > at the same time, but this only works with single requests, when I get 5 o 6 > threads working at the same time they just reach to a deadlock state every > time I try. > > Every thread stops at: > > Daemon Thread [http-8443-2] (Suspended) > DispatchQueue.dispatchEvent(EventManager$Dispatch) line: 53 > EventManager.dispatchEvent(EventManager$Dispatch) line: 359 > EventManager.postEvent(EventObject, EventSubject) line: 330 > DataContext(BaseContext).fireDataChannelChanged(Object, GraphDiff) line: > 349 > DataContext.fireDataChannelChanged(Object, GraphDiff) line: 1591 > DataContext.onContextFlush(ObjectContext, GraphDiff, boolean) line: 1060 > DataContext(BaseContext).onSync(ObjectContext, GraphDiff, int) line: 300 > DataContext.flushToParent(boolean) line: 1106 > DataContext.commitChanges() line: 1045 > > Except one that stops at: > > Daemon Thread [http-8443-3] (Suspended) > DataContextMergeHandler.graphChanged(GraphEvent) line: 103 > GeneratedMethodAccessor88.invoke(Object, Object[]) line: not available > DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 > Method.invoke(Object, Object...) line: 597 > Invocation.fire(Object[]) line: 202 > EventManager$Dispatch.fire(Invocation) line: 420 > DispatchQueue.dispatchEvent(Collection<Invocation>, Dispatch) line: 156 > DispatchQueue.dispatchEvent(EventManager$Dispatch) line: 57 > EventManager.dispatchEvent(EventManager$Dispatch) line: 359 > EventManager.postEvent(EventObject, EventSubject) line: 330 > DataContext(BaseContext).fireDataChannelChanged(Object, GraphDiff) line: > 349 > DataContext.fireDataChannelChanged(Object, GraphDiff) line: 1591 > DataContext.onContextFlush(ObjectContext, GraphDiff, boolean) line: 1060 > DataContext(BaseContext).onSync(ObjectContext, GraphDiff, int) line: 300 > DataContext.flushToParent(boolean) line: 1106 > DataContext.commitChanges() line: 1045 > > Maybe someone can help me with this deadlock or at least point me to a > different setup to bypass the thread safety errors I am having from time to > time. > > Thanks in advance. > Ramiro Aparicio >
