Re: using C11's _Atomic()

On Mon, May 04, 2026 at 11:39:59AM +1000, Tony Cook wrote:
[scary stuff about C++ compatibility]

Ok, my new plan for now is to add a PERL_ATOMIC() define, but not enabled
by default, nor via a configure probe. Instead it has to be explicitly
enabled via e.g. -Accflags='-DUSE_ATOMIC'. I will then use this to add
atomic to the  PL_sig_* vars, which will allow me to check that

    valgrind --tool=helgrind

runs cleanly. Currently it it is full of noise from the $thead->kill()
tests, thus masking whether there are any other issues.

So perl.h will have this added:

    /* Not ready for production use, so currently only enabled manually
     * rather than via a Configure probe.
     */
    #ifdef USE_ATOMIC
    #  include <stdatomic.h>
       /* 2 indicates guaranteed to be lock-free */
    #  if ATOMIC_INT_LOCK_FREE == 2 && ATOMIC_POINTER_LOCK_FREE == 2
    #    define PERL_ATOMIC(atype) _Atomic(atype)
    #  else
    #    define PERL_ATOMIC(atype) atype
    #  endif
    #else
    #  define PERL_ATOMIC(atype) atype
    #endif