> From: Melinda Shore <mshore@xxxxxxxxx>
> "Unix" ... was designed around a few abstractions, like pipes,
> filedescriptors, and processes, and by the time IP was implemented we'd
> pretty much settled on filedescriptors as endpoints for communications.
> We could do things with them like i/o redirection, etc. ... in Unix we
> shouldn't care whether an input or output stream is a terminal, a file,
> or a network data stream
Wow, that tickled some brain cells that have been dormant a very, very long
time! My memory of this goes all the way back to what I believe was the very
first mechanism added to V6 Unix to allow random IPC (i.e. between unrelated
processes), which was a pipe-like mechanism produced, if vague memories
serve, by Rand. This is all probably irrelevant now, but here are a few
memories...
One of the problems I recall we had with the Unix stream paradigm is that it
was not a very good semantic match for unreliable asynchronous communication,
where you had no guarantee that the data you were trying to do a 'read' on
would ever arrive (e.g. things like UDP), nor for things which were
effectively record-based (again, UDP).
Sure, TCP could reasonably well be coerced into a stream paradigm, but just
as RPC has failure modes that a local call doesn't, and therefore needs
extended semantics beyond that of a vanilla local call, so too it is with a
Unix stream (which, in V6, was the only I/O mechanism).
Noel
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