Hi Ben, thanks for the reply! No, the json object is not stored in the session, but it does traverse a lot of different components. The most likely cause seems to be from separate threads that we use to speed up data loading during a request, but we have not been able to pin it down - naturally we have not been able to reproduce this problem.
I have been considering using a different, thread safe data structure, but it is a lot of code to change. And we see this error only once every 2-3 weeks. We will have to spend more time trying to understand where this could happen. The reason I mentioned it here is that json is used a lot in ajax requests nowadays, so this seems like a problem that could arise in other situations as well. All the best, Adriaan On Tue, 5 Oct 2021 at 18:48, Ben Weidig <b...@netzgut.net> wrote: > Hi, > > is the JSONObject in the Session and do you have Session locking disabled? > See > > https://tapestry.apache.org/session-storage.html#SessionStorage-SessionLocking > > Changing the print-loop to check if keys still exist would just hide the > underlying problem: using a data-structure concurrently that isn't designed > to be used in a concurrent environment. > > Maybe you could use another type of thread-safe data structure in your > session, and convert it to a JSONObject before sending it back to the > client? > > Cheers, > Ben > > > On Tue, Oct 5, 2021 at 2:50 PM Adriaan Joubert <adriaan...@gmail.com> > wrote: > > > Hi, > > > > we intermittently see coercion errors for JSONObject - which we use > > frequently for ajax context information. > > > > The relevant bit of stack trace is > > > > - Caused by: java.util.ConcurrentModificationException > > - at > > > java.base/java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719) > > - at > > > java.base/java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:741) > > - at > org.apache.tapestry5.json.JSONObject.print(JSONObject.java:805) > > - at > > org.apache.tapestry5.json.JSONCollection.toString(JSONCollection.java:46) > > - at > > > org.apache.tapestry5.commons.internal.BasicTypeCoercions$1.coerce(BasicTypeCoercions.java:69) > > - at > > > org.apache.tapestry5.commons.internal.BasicTypeCoercions$1.coerce(BasicTypeCoercions.java:65) > > - at > > > org.apache.tapestry5.commons.services.CoercionTuple$CoercionWrapper.coerce(CoercionTuple.java:57) > > > > > > Overlapping calls mean the json object is modified in one place while it > is > > written elsewhere - as the objects themselves are not thread safe, it is > > quite messy to protect all possible writes. > > > > Copying the keys before the print loop, with a check that the value still > > exists when printing, would narrow the window for this to happen > > considerably. We could not think of any better solutions to solve this > > problem, but any suggestions are welcome. > > > > Cheers, > > > > Adriaan > > >
