RFR [9]: default Serialization should issue a fence after reconstructing an Object with final fields

[Chris Hegarty]

Additional note ( forgotten from original mail):

The fence is needed for "final-freeze" is a one-off barrier at the end of deserialization, similar that of constructors . Under normal circumstances the object being deserialized is not visible until deserialization completes, so you don't need a "freeze" until deserialization completes.

-Chris.

On 19 Feb 2015, at 16:25, Chris Hegarty <chris.hegarty at oracle.com> wrote:

> A number of years ago there was a proposal to use Unsafe.put*Volatile methods to set final fields during default deserialisation [1][2], but it never made it due to concerns about the potential negative impact of the additional fences. Now we have a, private, fences API in the platform, I think it is time to revisit this.
> 
> Webrev:
>  http://cr.openjdk.java.net/~chegar/deserialFence/webrev.00/webrev/  
> 
> Note: 
>  - Section 17.5.3 in the JLS [3], “Freezes of a final field occur both
>    at the end of the constructor in which the final field is set, and
>    immediately after each modification of a final field via reflection
>    or other special mechanism.” I believe this is a consequence of
>    the way in which setting of final fields is supported in the public
>    API, Field.setAccessible(), ( as defined by JSR 133 ) and should
>    not restrict an implementation from using a more performant
>    means, as is suggested here.  The statement in the JLS should
>    be revisited.
> 
> - Default Serialization already has a dependency on Unsafe, and
>   I don’t see this additional dependency as making that any worse. 
> 
> - Open question, should we include volatile fields as well as final?
> 
> - The changes in the webrev will issue a fence even if custom
>   deserialization is performed. I think this is ok, as it will be more
>   consuming to try to determine if a custom readObject set a final
>   through reflection, or not.
> 
> -Chris.
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-6647361
> [2] http://mail.openjdk.java.net/pipermail/core-libs-dev/2010-November/005292.html
>     http://mail.openjdk.java.net/pipermail/core-libs-dev/2010-December/005456.html
> [3] http://docs.oracle.com/javase/specs/jls/se8/html/jls-17.html#jls-17.5.3