Re: Automake's file locking

[Bruno Haible]

Zack Weinberg wrote:
> There is a potential way forward here.  The *only* place in all of
> Autoconf and Automake where XFile::lock is used, is by autom4te, to
> take an exclusive lock on the entire contents of autom4te.cache.
> For this, open-file locks are overkill; we could instead use the
> battle-tested technique used by Emacs: symlink sentinels.  (See
> https://git.savannah.gnu.org/cgit/emacs.git/tree/src/filelock.c .)

I can confirm that, while flock() is the most basic/elementary locking
facility [1], its emulation in gnulib [2] does not really work on
Solaris. The unit test regularly fails on Solaris.

Therefore I like the idea of merely relying on the atomicity of
file creation / file rename operations.

These files should reside inside the autom4te.cache directory. I would
not like to change all my scripts and Makefiles that do
  rm -rf autom4te.cache
to do something like
  rm -rf autom4te.cache autom4te.tmp.*
instead.

Bruno

[1] https://gavv.github.io/articles/file-locks/
[2] https://www.gnu.org/software/gnulib/manual/html_node/flock.html