Re: [infinispan-dev] Infinispan's dependency injection fwk
>> 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?
Piggybacking is a valid strategy and is used in some core JDK constructs including
AbstractQueuedSynchronizer, which is used to build locks, etc. See Java Concurrency in
Practice, section 16.1.4:
http://codeidol.com/java/java-concurrency/The-Java-Memory-Model/What-is-a...
More fun reading:
http://gee.cs.oswego.edu/dl/jmm/cookbook.html
Piggybacking still requires a
sync/volatile variable to be touched by both threads in order for the publishing to to be
correct (int the AbstractQueueSynchronizer/FutureTaks example, a volatile variable is set
to null when reading/writing state, just to enforce happens-before).
To be more specific, here the safe publishing issue that concerns me:
T1 creates the Cache on DCM.getCache(). This calls @Inject method on CacheDelegate that
would set CacheDelegate.invoker::InterceptorChain. N.B. invoker is not final nor
volatile!
T2 calls CacheDelegate.put, which uses the invoker field set by T1. What guarantee do we
have that invoker was correctly published by T1 and seen by T2?
Looking at the code, the safe publishing takes place in DefaultCacheManager.caches field:
this is CHM where T1 added the cache and T2 got it from - so we're safe (published)!
One more detail, in the same class DefautlCacheManager.globalComponentRegistry doesn't
seem to be correctly published (it is not a immutable object as well): this is created by
T1 on new DCM and read by T2 when a Cache is instantiated, with no happens-before in
between. I think we should declare it volatile.
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