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Re: patch to support output synchronization under -j

From: Paul Smith
Subject: Re: patch to support output synchronization under -j
Date: Thu, 14 Apr 2011 15:16:36 -0400

On Thu, 2011-04-14 at 14:08 -0400, David Boyce wrote:
> On Thu, Apr 14, 2011 at 1:29 PM, Paul Smith <address@hidden> 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 <address@hidden>          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

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