Re: `message' not outputting the newline "atomically"

[Paul Eggert]

Eli Zaretskii wrote:
> What exactly is the problem you would like to fix here?

$ strace -o /tmp/tr emacs -Q -batch -eval '(message "hello")'
hello
$ grep '^write(2,' /tmp/tr
write(2, "hello", 5)                    = 5
write(2, "\n", 1)                       = 1

There should be just one 'write' system call, not two. Because of this problem, 
if two Emacs processes output the lines "foo" and "bar" to the same file 
descriptor at nearly the same time, the output might be "foobar\n\n" or 
"barfoo\n\n" rather than the more-desirable "foo\nbar\n" or "bar\nfoo\n". This 
can cause the annoying symptoms that Lars reported in 
<https://lists.gnu.org/r/emacs-devel/2019-06/msg00710.html>.

I fixed it on GNU and similar platforms by installing the attached patch into 
Emacs master. I fixed some other minor stdio glitches while I was in the 
neighborhood.

0001-Line-buffer-stderr.patch
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