DMD 1.029 and 2.013 releases

[Russell Lewis]

Sean Kelly wrote:
> 1) The cost of acquiring or committing a lock is generally roughly equivalent to
>      a memory synchronization, and sometimes less than that (futexes, etc).  So
>      it's not insignificant, but also not as bad as people seem to think.  I suspect
>      that locked operations are often subject to premature optimization.

What exactly do you mean by "memory synchronization?"  Just a write 
barrier instruction, or something else?

If what you mean is a write barrier, then what you said isn't 
necessarily true, especially as we head toward more and more cores, and 
thus more and more caches.  Locks are almost always atomic 
read/modify/write operations, and those can cause terrible cache 
bouncing problems.  If you have N cores (each with its own cache) race 
for the same lock (even if they are trying to get shared locks), you can 
have up to N^2 bounces of the cache line around.