Re: confusion about message passing between the tasks

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> You cannot program in a procedural way with PO. You can implement
> equivalent semantics, possibly, but not the program structure.
>
> An extreme scenario (unfortunately not Ada's annex E), a distributed system
> could be decomposed around rendezvous between tasks running on physically
> distributed nodes. This cannot be done with PO.

I implemented such a system (distributed tasks) for Ada 83.

The main problem is shared variables:  In Ada, you can't tell which
variables are shared.  And shared variables across a distributed
system either don't work, or are grossly inefficient.

Annex E solves that problem:  No shared variables across partitions
(except in the special case of Shared_Passive, which presumes the
partitions are on the same machine, so can map shared areas of memory).

- Bob