On Wed, Nov 03, 2021 at 07:23:23PM -0700, Carlo Arenas wrote:
> > diff --git a/run-command.c b/run-command.c
> > index 7ef5cc712a9..a82cf69e7d3 100644
> > --- a/run-command.c
> > +++ b/run-command.c
> > @@ -1099,7 +1099,7 @@ static NORETURN void die_async(const char *err, va_list params)
> > static int async_die_is_recursing(void)
> > {
> > void *ret = pthread_getspecific(async_die_counter);
> > - pthread_setspecific(async_die_counter, (void *)1);
> > + pthread_setspecific(async_die_counter, &ret); /* set to any non-NULL valid pointer */
>
> I guess this would work, since the pointer is never dereferenced, but
> the use of (void *)1 was hacky, and this warning seems like the right
> time to make it less so.
>
> Would a dynamically allocated pthread_local variable be a better
> option, or even a static global, since we don't care about its value
> so no need to worry about any races?
Yeah, I had the same thought. I think what's in the patch above is OK in
practice, but it sure _feels_ wrong to store the address of an auto
variable that goes out of scope.
I'm OK with it as a minimal fix, though, to get things unstuck. The
commit message nicely explains what's going on, and the original (which
it looks like blames to me ;) ) is pretty gross, too.
Keeping an actual counter variable would be the least-confusing thing,
IMHO, but that implies allocating per-thread storage (which means having
to clean it up). And we really only care about counting up to "1", so
the boolean "do we have a pointer" is fine. The static variable you
suggest might be a good middle ground there, and we could even use it
for the comparison to make things more clear. Something like:
static int async_die_is_recursing(void)
{
static int async_recursing_flag;
void *ret = pthread_getspecific(async_die_counter);
pthread_setspecific(async_die_counter, &async_recursing_flag);
return ret == &async_recursing_flag;
}
But I don't feel that strongly either way.
-Peff
