On: Tell HN: C Experts Panel – Ask us anything about C

[rwmj]

I believe the last proposal was in 2008 (ignore the try..finally stuff here): http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1298.pdf

So I guess it needs someone to take that and update it, also to pull up a full list of current Linux software which is using this feature (which as I say these days is a surprising amount).

[eqvinox → rwmj]

Here's our usage: https://github.com/FRRouting/frr/blob/master/lib/privs.h#L14...

  #define frr_with_privs(privs)                                                  \
          for (struct zebra_privs_t *_once = NULL,                               \
                                    *_privs __attribute__(                       \
                                            (unused, cleanup(_zprivs_lower))) =  \
                                            _zprivs_raise(privs, __func__);      \
               _once == NULL; _once = (void *)1)

This gives us a block construct that guarantees elevated privileges are dropped when the block is done:

  frr_with_privs(privs) {
    ... whatever ...
    break;  /* exit block, drop privileges */
    return; /* return, drop privileges */
  }

[rwmj → eqvinox]

We have a nice macro for acquiring locks that only applies to the scope:

https://github.com/libguestfs/nbdkit/blob/e58d28d65bfea3af36...

You end up with code like this:

https://github.com/libguestfs/nbdkit/blob/e58d28d65bfea3af36...

It's so useful to be able to be sure the lock is released on all return paths. Also because it's scope-level you can scope your locks tightly to where they are needed.

[loeg → rwmj]

We use it extensively in our proprietary codebases as well, FWIW. Not real open data for me to point to, but: a few million lines of C, and a handful of billion USD in revenue. If that helps weigh in on "yes, please standardize this common practice."