Paul Eggert <eggert@xxxxxxxxxxx> writes: > > I'm thinking of older systems. As far as I know SA_RESTART was > > introduced by Solaris. I doubt it is in SVR4.2, for example, though I > > admit that I don't have a way to check. > > Rich Stevens wrote in 1991 that SA_RESTART was in SVID Issue 3, > in SVR4, and in 4.3BSD Reno. See: > <http://groups.google.com/groups?selm=1991Jul31.185303.5583%40noao.edu> Ah, OK. I have SVID Issue 2, which doesn't have it. > > I checked Ultrix 4.0, and it has sigaction but does not have SA_RESTART. > > That was released in 1990, right? It was probably based on 4.3BSD > Tahoe then, and I guess Tahoe didn't have it. Reno came out in June 1990. I think it's actually based on 4.2BSD, with a lot of stuff added on for increased System V compatibility. > > AC_DEFUN([AC_SYS_RESTARTABLE_SYSCALLS], > > [AC_DIAGNOSE([obsolete], > > [$0: System call restartability is now typically set at runtime. > > Remove this `AC_SYS_RESTARTABLE_SYSCALLS' > > and adjust your code to use `sigaction' with `SA_RESTART' instead.])dnl > > Perhaps that's a bit draconian. Can you suggest a better wording for > that diagnostic? How about something like this: $0: AC_SYS_RESTARTABLE_SYSCALLS is only useful when supporting old systems which do not provide `sigaction'. Don't use this macro unless you intend to support very old systems. The point is that people shouldn't check AC_SYS_RESTARTABLE_SYSCALLS because they want restartable system calls. They should check it to see if that is all they can expect. (I think that restartable system calls are a superficially attractive idea which interacts poorly with the Unix I/O interface, because they leave you with no good way to do a timed read or write. If Unix had a standard interface for a timed read/write of up to N characters, then restartable system calls make a lot of sense. Admittedly efficient Unix serial I/O is a black art anyhow.) > Wouldn't it be better for uucp to determine the value dynamically? > That should be fairly easy to do, by running a bit of test code. Then > you wouldn't need to guess, and you wouldn't need > AC_SYS_RESTARTABLE_SYSCALLS either. (You would need an ancient system > to test it on, but I guess if you have Ultrix 4.0 then that is ancient > enough. :-) I couldn't think of any dynamic test which ran quickly. Note that the autoconf test takes a few seconds. It's not worth taking a few seconds to run a dynamic test every time uucico starts up to make a serial connection. Ian
