> That wasn't my point.  My point was that there is no return channel.
> If you want to know when your write is done, you have to use a lock
> or a memory barrier.  Both are very expensive.

Barriers of synchronisation are a little expensive (one of the main 
drawbacks with a too restricted way of communication) but have many
advantages as deadlock free and possibility to optimized the 
"communications" (copy of the data in the shared memory or juste the 
pointer).

FG