[cpp-threads] D2335 (sequential consistency proof) revision

[Boehm, Hans]

> From: Chris Thomasson
> 
> [...]
> 
> Taking a lock does not necessarily require a #StoreLoad | #StoreStore 
> barrier. There are asymmetric locking algorithms in which 
> certain thread(s) 
> can take the lock without using interlocked rmw or store/load 
> memory barrier 
> instructions. 
> 
You're presumably talking about cases in which a thread knows that it
held the lock last?  Otherwise you inherently need to do something to
ensure that a lock acquisition and a subsequent memory operation M don't
become visible out of order to the previous thread to release the lock,
i.e. that it doesn't see M before the lock release.  On many
architectures that does require a fence or some other kind of ordered
memory operation, right?

Hans