Re: [PATCH nft 2/4] gmputil: add nft_gmp_free() to free strings from mpz_get_str()

[Phil Sutter <phil@nwl.cc>]

On Wed, Sep 20, 2023 at 04:46:12PM +0200, Thomas Haller wrote:
> On Wed, 2023-09-20 at 16:05 +0200, Phil Sutter wrote:
> > On Wed, Sep 20, 2023 at 03:13:39PM +0200, Thomas Haller wrote:
> > > 
> > > +       mp_get_memory_functions(NULL, NULL, &free_fcn);
> > 
> > Do we have to expect the returned pointer to change at run-time?
> > Because
> > if not, couldn't one make free_fcn static and call
> > mp_get_memory_functions() only if it's NULL?
> 
> Hi Phil,
> 
> 
> no, it's not expected to EVER change. Users must not change
> mp_set_memory_functions() after any GMP objects were allocated,
> otherwise there would be a mixup of allocators and crashes ahead.
> 
> However, I didn't cache the value, because I don't want to use global
> data without atomic compare-exchange (or thread-local). Doing it
> without regard of thread-safety so would be a code smell (even if
> probably not an issue in practice). And getting it with atomic/thread-
> local would be cumbersome. It's hard to ensure a code base has no
> threading issues, when having lots of places that "most likely are
> 99.99% fine (but not 100%)". Hence, I want to avoid the global.

OK, thanks.

> I think the call to mp_get_memory_functions() should be cheap.

Yes, the function is indeed very simple.

Cheers, Phil