libthr shared locks

[Martin Simmons]

>>>>> On Mon, 15 Feb 2016 16:44:10 +0200, Konstantin Belousov said:
> 
> On Mon, Feb 15, 2016 at 02:17:20PM +0000, Martin Simmons wrote:
> > 
> > Also, a general question: why not use some flag in the barrier (and other
> > objects) to indicate pshared, removing the need for __thr_pshared_offpage
> > except in init?
> 
> But where would I keep the object ? All that I have with the current
> ABI is a single pointer, which de facto behaves like the flag which you
> proposed. It is either real pointer or (if set to some specific value
> impossible for a valid pointer) there is an offpage.

I'm probably missing something, but I was thinking pthread_barrier_init would
do something like

if ( attr is PTHREAD_PROCESS_PRIVATE ) {
   bar = calloc(1, sizeof(struct pthread_barrier));
   pshared = 0;
} else {
   bar = __thr_pshared_offpage(barrier, 1);
   pshared = 1;
}
bar->psharedflag = pshared;
*barrier = bar;

Then pthread_barrier_destroy would use the psharedflag slot to decide how to
free it and pthread_barrier_wait would need no changes.