They can't be final. The whole point of injecting stuff is that components go through
a lifecycle:
1) Configure. This is where components are created and wired together.
2) Start.
Now in between 1 and 2, if someone still has a reference to the Configuration instance and
changes some stuff, these changes would need to be reflected in the runtime. Which means
some components may need to be re-injected with different implementations.
In terms of safe publishing, you can consider this safe since in the start method of the
ComponentRegistry, internal volatile fields (including some locks) are touched, which
means a JMM fence [1] is crossed. So even non-volatile variables would be properly
published by this time since all out-of-order operations need to complete for the fence.
Now normally this would be considered hackish since subsequent writes to the variables in
question may not be published properly, however we ensure that the ComponentRegistry is
the only component capable of injecting stuff, and the CR will make sure there is a fence
every time.
HTH
Manik
[1]
http://en.wikipedia.org/wiki/Memory_barrier
On 22 Jul 2010, at 17:22, Mircea Markus wrote:
Hi,
I have this problem with the the dependency injection fwk in infinispan: many times
I'd like to declare the injected dependencies as final fields in order to take
advantage[1] of "final" semantics in Java's memory model. I cannot/don't
know how to do that, can I annotate an constructor with @Inject? If not I think that would
be useful.
[1] @Inject methods are called by the thread that starts the CM. The injected
dependencies are cached as local fields and will be accessed by a different application
thread. So they'd need volatile/synchronise for proper publishing: afaik volatile is
less performant that publishing with final.
wdyt?
Cheers,
Mircea
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Manik Surtani
manik(a)jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
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