Volatile Read Implications

[wsugarman]

I was recently reading Lazy.cs and noticed that the member _state is volatile. I think this is done to ensure proper acquire semantics and release semantics (as per the language specification) for the Value property. More specifically, if _state is null, it must mean that _value is non-null, because _state is assigned last and none of the other writes like _value can be reordered after it (there are also helpful comments to emphasize this point).

However, does the volatile keyword also imply any behavior about the "freshness" of the other members access by a given thread? Is it possible that an old value of the non-volatile member _value is cached in some register by the time we read it? Perhaps this is processor-specific?

I see that there are really three code paths for Lazy<T> values, so are there "freshness" guarantees made through the use of a lock for LazyThreadSafetyMode.ExecutionAndPublication and Interlocked for LazyThreadSafetyMode.PublicationOnly that are not present for LazyThreadSafetyMode.None?

[huoyaoyuan]

The CLR memory model documentation (#75790) may provide some help for you.