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
