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Re: [bug #60774] make hangs on fcntl lock when using -O and stdout is /d

From: Dmitry Goncharov
Subject: Re: [bug #60774] make hangs on fcntl lock when using -O and stdout is /dev/null
Date: Sun, 25 Jul 2021 16:04:51 -0400

On Sun, Jul 25, 2021 at 3:25 PM Paul Smith <psmith@gnu.org> wrote:
> I have no problem with make refusing to write to a device that's locked
> in general.  If users don't want that to happen, they can just not use
> the -O option.

True, as long as the user knows that when -O is specified make is
going to lock stdout.

> It's clear that /dev/null is a special case, however, because the order
> in which data is written to it cannot be detected so what's the point
> in preserving any order?

Maybe Mike can tell us.

> What I'm saying is that IF make can detect that its stdout is going to
> /dev/null then it shouldn't lock at all, because it's not necessary to
> do so in order to meet the goals of the -O option, and doing so
> introduces unnecessary latency in the build.

Even if we come up with a portable mechanism to detect /dev/null, what
about other files?
What about /dev/stdout or /dev/pts/5?
i don't think, it is possible or even reasonable to attempt to special
case all these files.

> The  question is what to do about supporting -O on these systems.

A private temp file will work.

> That's true but there are, unfortunately, some edge cases where Windows
> and POSIX systems behave differently.

True. Is this case really one of those edge cases?

>  The goal is to provide  the best implementation of make for the GNU system

What do you think we should do about this bug report?

regards, Dmitry

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