[TUHS] non-blocking IO

[Paul Ruizendaal]

>     > when you're working below the reliable stream level, you can't just do a > blocking 'read' for a packet; it pretty much has to be asynchronous
> Oh, you should look at the early BBN TCP for V6 Unix - they would have faced the same issue, with their TCP process. They did have the capac() call (which kind of alleviates the need for non-blocking I/O), but that may have only been available for ports/pipes; I'm not sure if the ARPANET device supported it.

I did. There is capac() support also for the IMP interface:
https://www.tuhs.org/cgi-bin/utree.pl?file=BBN-V6/dmr/imp11a.c
(see bottom two functions)

BBN took the same approach as Research: with capac() or select() one can prevent blocking on read() and write().