Re: Make run in parallel mode with output redirected to a regular file can randomly drop output lines

[Frank Heckenbach]

(Sorry, I can't reply properly; I'm not subscribed, just saw the
message on the web archive.)

Stefano Lattarini wrote:

> Make run in parallel mode with output redirected to a regular file
> can randomly drop output lines

Yet another reason to use the new --output-sync feature. :)

I hadn't actually thought about this particular problem when I got
interested in the feature, but it makes sense. Perhaps I had
occasionally lost some messages before and never noticed ...

> The issue is present both in all of make 3.81, make 3.82 and make
> built from latest Git.  Here is a script that demonstrates it:
>
> [...]
>
> and the following suggests it might not be easy to fix:
>
>   <http://lists.gnu.org/archive/html/automake-patches/2009-03/msg00073.html>

As Ralf Wildenhues explains in that mail, it's not really a make
problem, but the behaviour of POSIX files, also "Using O_APPEND
avoids this race", i.e. in your demo script, using ">>" (and
clearing the target file before) would also fix the problem.

> But it's worth nothing that the issue is not present with FreeBSD make (as
> offered by Debian package freebsd-buildutils 9.0-11); maybe the sources of
> that package might suggest how to obtain a fix after all?

I suppose it does something similar to our output-sync, i.e.
directing the output from different jobs to different temp files and
dumping it to the original stdout/stderr synchronized. Or do you
have something else in mind that make should (and could) do?