A possible deadlock was detected when new types are registered during multithreading activity against ObjectDB.
Until this issue is fixed, the recommended workaround is to complete registration of all the persistable types before starting any multithreading activity against ObjectDB.
A single class can be registered by:
emf.getMetamodel().entity(MyClass.class);
All the classes can be registered by:
emf.getMetamodel().getManagedTypes();
The last command will work when ObjectDB can find managed classes automatically.
ObjectDB Support