[dmd-concurrency] draft 7

[Andrei Alexandrescu]

Fawzi Mohamed wrote:
> I gave a quick reading about the fact that reading needs a lock because 
> otherwise it might not be updated almost forever, this is (as far as I 
> know) wrong.
> Yes the view of one thread might be offset with respect with the one of 
> another, but not indefinitely so.
> The main reason to put the sync is to ensure that one sees a consistent 
> view of the value.
> If a value is always updated in an atomic way then the sync is not needed.

It's a classic that if you read (without handshake) a value in a loop 
thinking you're doing spinning, various compiler and processor 
optimizations will cache the value and spin forever. The synchronization 
in there is needed for the handshake, and can be optimized by the 
compiler if a simple barrier is needed.

But no handshake == incorrect code.


Andrei