2010/7/23 Mircea Markus <mircea.markus(a)jboss.com>:
On 22 Jul 2010, at 19:07, Manik Surtani wrote:
> 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.
changes stuff means it changes the Configuration object itself or some of its
attributes?
> 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.
Afaik safe publishing would only happen if *same* variables are touched by the user's
thread accessing the object, is that the case?
It's ok if the variable is different than the one you're going to send
over, what you have to guarantee is that T1 writes to a variable X
before T2 reads *the same* variable X, but other variables after that
will also get the guarantee of safe publishing.
Here is a good explanation:
http://jeremymanson.blogspot.com/2008/11/what-volatile-means-in-java.html
> 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variables in question may not be published properly, however we ensure that the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
>
http://www.jbosscache.org
>
>
>
>
>
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