Perform read/write locking of CDO attribute dictionary
We currently rely on semantic guarantees that the CDO dictionary is used read-only after SEAL; instead, the struct mstro_attribute_dict_
should have an pthread_rwlock_t
member and we accessors should use that.
Currently ThreadSanitizer shows a read/write data race on dictionary reads for local-size and the corresponding 'insert-default' path in some cases (empty CDOs, mainly).