[hibernate-dev] Fences API to threadsafely initialize no-argument constructor objects

[Sanne Grinovero]

Hi Hardy,
sorry for the late answer, I remember some discussions between us
about the coming of an API to help us with threadsafe objects
which couldn't use contructor initialization (and hence final fields)
but wasn't able to find the API back I spoke about.

The javadoc for jsr166y : http://gee.cs.oswego.edu/dl/jsr166/dist/jsr166ydocs/
but the API I was most interested in somehow disappeared and I
couldn't remember the name.
It is called Fences (at list  the article back) and is an extension of jsr166y
Quoting part of the javadoc:

"With care, a fence may be used to obtain the memory safety effects of
final for a field that cannot be declared as final, because its
primary initialization cannot be performed in a constructor, in turn
because it is used in a framework requiring that all classes have a
no-argument constructor. "

http://gee.cs.oswego.edu/dl/jsr166/dist/docs/java/util/concurrent/atomic/Fences.html

the problem is that jsr166y is a preview of the concurrency APIs of
Java7, and as such can be backported
(there's a jar already you could depend on to make it work on JDK 5
and 6), but the Fences
rely on JVM support so they can't be backported: so they are not
included in jsr166y.
That makes it quite useless for Search and Bean Validation :-( but
it's still interesting to read about it
as Fences documentation is a good reference for all the pitfalls in
design of a "framework requiring that all classes have a no-argument
constructor".

regards,
Sanne