Re: Redesign of 3.2 to eliminate file descriptor objects Marc Nieper-WiÃkirchen 03 Oct 2020 20:25 UTC
PS call-with-fd tries to achieve something which it cannot guarantee, namely that the fd will be finally closed. So if such a procedure is provided at all (which I wouldn't), it makes more sense to just call it, say, "port-dup" and so that it just returns a duplicated fd. In order to make sure that no resource is claimed forever, we should rather standardize something like guardians for R7RS-large, which will be a solution not only for fds to eventually collect resources. Am Sa., 3. Okt. 2020 um 19:54 Uhr schrieb Marc Nieper-Wißkirchen <email@example.com>: > > Am Sa., 3. Okt. 2020 um 19:26 Uhr schrieb John Cowan <firstname.lastname@example.org>: > > >> The only procedures that remain that deal with > >> fds are fd->port and with-port-fd. It could make sense to move them > >> into a separate lower-level SRFI. > > > > > > fd->port is important because fds are part of the external interface of a program. Normally we only say what use is made of ports 0 and 1, because they are always connected internally. > > I understand its importance. If there won't be a SRFI dealing with the > low-level fds, I agree that it should stay in this SRFI. > > >> Especially `with-port-fd' is fragile > >> and shouldn't be exposed to the user. If a non-continuable exception > >> is raised, while `proc' is executing, [...] > > > > > > That's quite true, and is a general problem with call/cc: it does not interoperate well with anything resembling try-finally or unwind-protect The existing call-with-port procedure has exactly the same issues, as do its trivial derivatives call-with-*-file and with-*-from file. > > call-with-port isn't at all that problematic because the port object > is known to the garbage collector, which will close the port when > there is no reference to it anymore. > > > As an aid to recovery from such situations, I have added back close-fd. I have also renamed with-port-fd to call-with-port-fd and pointed out the symmetry with call-with-port. > > The symmetry seems only superficial. > > >> There is > >> no way to sensibly use `with-port-fd' just with SRFI 170 anyway. > > > > > > That's true, and I am still open to getting rid of it altogether. It is, however, a low-level building block for other SRFIs. > > The latter s certainly true but that does not mean at all that it has > to be exposed to the user-visible API. > > If we see a few other low-level SRFIs like 170, it may very well be > that they may have to communicate with each other behind the scenes > (meaning that their implementations cannot be totally independent), > but that's absolutely fine. With this low-level stuff, I firmly > believe that any goal to allow implementations to be independent up to > the user-visible API is a misguided one when it forces to expose > fragile things like `with-port-fd' to the user.