1. Because it's simpler to explain. That's a weak argument: a textbook could
start with the simple rules in Eric's message and then go into more complex
mechanisms. If pushed, I am even willing to reorganize accordingly the draft.
2. Because it's simpler to implement. Somebody wants to make this case? I
think we still need the same machinery.
3. Because the restriction causes no loss of important function. But I
understand from the Cray people that (put/get, barrier)* style is quite