Util.readField is not thread-safe

[arjenvanderende]

We're running a high traffic website hosted on Google AppEngine. When saving an object to the datastore we frequently (every few minutes) run into the follow exception:

siena.SienaException: java.lang.SecurityException: Unable to access relation
    at siena.Util.readField(Util.java:307)
    at siena.gae.GaePersistenceManager.update(GaePersistenceManager.java:508)
    at siena.gae.GaePersistenceManager.save(GaePersistenceManager.java:905)
    at siena.core.PersistenceManagerLifeCycleWrapper.save(PersistenceManagerLifeCycleWrapper.java:110)
    at siena.Model.save(Model.java:87)

From the source I see that Util.readField temporarily makes a Field accessible when a field is non-accessible. I believe that the exception we see is a race condition between two threads where the second thread resets the access of a field (after completing it's .get), when the first thread is just about to .get the value of the same field.

I don't expect this issue to be resolved, but I'm documenting it here for future reference.

[ZiglioUK]

I've often seen this error. Good suggestion about a threading situation.
I must have surrounded it with a catch, you can see my latest version here:
https://github.com/siena/siena/tree/async