---------- Forwarded message ---------- From: Tim Murphy <tnmur...@gmail.com> Date: 14 April 2011 20:43 Subject: Re: patch to support output synchronization under -j To: psm...@gnu.org
The reason for splitting stderr and stdout is to do with deadlock and reading pipes. IIRC. e.g. blocking on a read to stderr which will never return because the process is stuck waiting for you to read from it's stdout. I think it's all easier on an os where you can create ptys (is that the term?) i.e. fake "consoles" to which stdout and stderr are both attached. I am going to be lazy and let someone else justify this or shoot it down. Perhaps I will remember why I got into trouble with it a long time ago. In practice the non-interleaving is actually nice in examples I've seen because the context is obvious from the error message itself (otherwise its' a crap error message and needs updating) and the division makes it a little easier to scan for error messages automatically. It's more of a problem where you're running a task that executes some long sub-build. Regards, Tim On 14 April 2011 20:16, Paul Smith <psm...@gnu.org> wrote: > On Thu, 2011-04-14 at 14:08 -0400, David Boyce wrote: >> On Thu, Apr 14, 2011 at 1:29 PM, Paul Smith <psm...@gnu.org> wrote: >> > One example: I think saving stdout and stderr to different files and >> > then printing them separately is problematic; consider if your recipe >> > prints lots of information lines, with errors (to stdout) interspersed. >> > If you throw all the errors to the end you lose a lot of context. >> >> The reason is that the SHELL variable is used not only for recipes but >> also for the $(shell) function. Intermingling stdout and stderr in the >> result of $(shell) is just disastrously wrong (as I found in the first >> iteration of syncsh). I spent some time trying to find a way to >> determine, from inside a child shell, whether we were forked by a >> recipe or by $(shell) but could find no reliable way. Thus syncsh was >> forced to keep them in separate files. Since $(shell) invocations are >> not "jobs" according to make's process model there's no need for them >> to participate in synchronization at all, so it may be that within >> make there's a way to only sync on recipes which in turn would allow >> 2>&1. > > Your latter statement is absolutely correct: it's wrong for $(shell ...) > to synchronize. Shell function output is captured by make, not printed > to stdout, so synchronizing it doesn't make much sense. > >> Of course, either way some context is lost. If you put both into one >> temp file you lose track of which was which; if you keep them in >> separate files you lose ordering instead. So it becomes a matter of >> taste, or perhaps an option though that seems like a bit too much to >> me. > > I agree that adding an option seems like a lot. > > I think it's more important to maintain ordering of stdout/stderr than > it is to allow individual redirection. > > However, you could do both with some heuristics. Hm. Maybe not. I was > going to say you could merge them if stdout and stderr were going to the > same tty or file, but I don't think there's any good way in UNIX to know > whether two file descriptors are pointing at the same file/device. Hrm. > In Linux you can find out via /proc but that's a pretty special case. > > -- > ------------------------------------------------------------------------------- > Paul D. Smith <psm...@gnu.org> Find some GNU make tips at: > http://www.gnu.org http://make.mad-scientist.net > "Please remain calm...I may be mad, but I am a professional." --Mad Scientist > > > _______________________________________________ > Bug-make mailing list > Bug-make@gnu.org > http://lists.gnu.org/mailman/listinfo/bug-make > -- You could help some brave and decent people to have access to uncensored news by making a donation at: http://www.thezimbabwean.co.uk/ -- You could help some brave and decent people to have access to uncensored news by making a donation at: http://www.thezimbabwean.co.uk/ _______________________________________________ Bug-make mailing list Bug-make@gnu.org http://lists.gnu.org/mailman/listinfo/bug-make