[Info-vax] CRTL and RMS vs SSIO

[Lawrence D’Oliveiro]

On Sunday, October 10, 2021 at 5:47:14 AM UTC+13, Stephen Hoffman wrote:
> Punched cards and punched-card-based assumptions are rather more 
> pernicious within OpenVMS and clustering, and mailboxes, and various 
> other areas, alas. For those of us steeped in OpenVMS, the effects of 
> these assumptions can be invisible.

E.g. VMS mailboxes are record-based, whereas on *nix, pipes (both named and unnamed) are stream-based. PF_UNIX sockets can be either stream or datagram (record)-based. As for network connections, TCP is stream-based, but I think UDP is datagram-based. (AppleTalk? I could tell you stories about AppleTalk...)

I have heard tell of newbie TCP programmers assuming that messages they send in one operation will be received in their entirety in one operation ... wonder how long it takes before they discover that’s not true ...

> Back to RMS and SSIO, apps that don't expect punched-card semantics can 
> and variously do perform their own coordination, so sharing the 
> underlying files with apps that do expect punched cards is unnecessary, 
> and counterproductive.

I don’t think it has been traditional on *nix systems to bother with much (if any) locking at all, at least not at the file I/O level. There has never been anything on such systems (that I have seen) like the VMS Lock Manager, distributed or otherwise. Any more elaborate locking protocol needed would be implemented through the subsystem’s own custom server processes.