On Feb 20, 2012, at 16:20 , Christopher Smith wrote: > Message objects *don't* have mutators and are conceptually a copy of the > relevant builder object.
Having attempted to refresh my knowledge of the Java Memory Model, I think there is a subtle difference between an object that has all final fields, and an "immutable" object like the protobuf messages. However, I don't think it matters in reality: As long as the message is "correctly published" to other threads (eg. a synchronized block, volatile reference, concurrent data structure), then everything is fine. Since everyone *should* be doing this already, Messages are safe to use across multiple threads. Evan PS. For language lawyers: I *think* the potential difference is as follows: Writes to final fields in a constructor are guaranteed to be visible to all threads when the constructor exits. So if you had the following: static FinalImmutableObject someRef = ...; Then if another thread sees a non-null value for someRef, it will correctly see all the values of the final fields. On the other hand, if you do this with a protobuf message, it *theoretically* could see a non-null value for someRef, but still see uninitialized or incorrectly initialized values for fields in someRef. This is because this static variable is not synchronized or volatile, so there is no "happens-before" relationship between two threads. Thus, the reads on one thread *could* be reordered before the writes on the other thread. References: http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4 http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.5 -- http://evanjones.ca/ -- You received this message because you are subscribed to the Google Groups "Protocol Buffers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
