[Info-vax] VMS process communication

[Simon Clubley]

On 2022-09-13, Bob Gezelter <gezelter at rlgsc.com> wrote:
>
> My compliments. I know all too well how much effort it takes to produce such a compendium.
>
> As has been observed, mailboxes are not included.
>
> DECnet Task-to-Task would also make a useful addition. While DECnet does
> not include encryption, an omission that I have been quietly outraged by
> for decades, when tunneled over an encrypted IP tunnel OR used locally, it
> is quite useful. DECnet logical links are message-based, unlike
> stream-based TCP sockets, which does simplify programming to an extent.

However, encryption only protects the data while it is in transit. It does
nothing to stop attacks against the protocol stack in the target server
itself if the client has access to the target server.

>
> Both network-based techniques have a significant synchronization
> advantage over shared memory techniques. When either partner of a TCP
> socket or a DECnet logical link exits, the corresponding partner is
> automatically notified, allowing the appropriate steps to be taken.
> Detecting a failed correspondent is far more complex with shared memory
> techniques. Network links are also atomic. A message is sent or not, there
> are no partial messages. Shared memory approaches have the inherent danger
> that an update may be incomplete, corrupting the shared data structure.
>

The no-partial-message guarantee is only true for stream protocols if you
implement something on top of the stream protocol that guarantees you have
received a full message.

In a stream protocol, just because the transmitter sent 4000 bytes, there's
no guarantee that all 4000 bytes were delivered to the receiver before
some connection interruption occurred.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.