Re: [PATCH] Correctly initialize 'installed_handlers'

[Junio C Hamano <gitster@pobox.com>]

Carlo Marcelo Arenas Belón <carenas@gmail.com> writes:

> the way this is handled would seem to indicate otherwise
>
> if (!installed_handlers) {
>                 atexit(remove_tmp_objdir);
>                 sigchain_push_common(remove_tmp_objdir_on_signal);
>                 installed_handlers++;
> }

It is a curious piece of code.  

The "prepare a file-scope static and do something and increment it
when it is 0" pattern expects the function to be called many times
and do the guarded thing only once.  However, there is this code:

	if (the_tmp_objdir)
		BUG(...);

before we do anything else, and then before that "arrange to clean
up, but do so just once" block, there is

	the_tmp_objdir = t;

where t is the pointer to a "struct tmp_objdir" instance.  So one
part of the function expects to be called at most once, while
another part is prepared to be called more than once.

Almost all of this function is attributed to 2564d994 (tmp-objdir:
introduce API for temporary object directories, 2016-10-03), so
let's see if Peff remembers anything about this curiosity.

Thanks.