static void lock_ool(volatile AO_TS_t *l)
{
int i = 0;
while (AO_test_and_set_acquire(l) == AO_TS_SET)
AO_pause(++i);
}
AO_t *
AO_stack_pop_explicit_aux_acquire(volatile AO_t *list, AO_stack_aux * a)
{
unsigned i;
int j = 0;
AO_t first;
AO_t * first_ptr;
AO_t next;
retry:
first = AO_load(list);
if (0 == first) return 0;
/* Insert first into aux black list. */
/* This may spin if more than AO_BL_SIZE removals using auxiliary */
/* structure a are currently in progress. */
for (i = 0; ; )
{
if (PRECHECK(a -> AO_stack_bl[i])
AO_compare_and_swap_acquire(a->AO_stack_bl+i, 0, first))
break;
++i;
if ( i >= AO_BL_SIZE )
{
i = 0;
AO_pause(++j);
}
}
assert(i < AO_BL_SIZE);
assert(a -> AO_stack_bl[i] == first);
/* First is on the auxiliary black list. It may be removed by */
/* another thread before we get to it, but a new insertion of x */
/* cannot be started here. */
/* Only we can remove it from the black list. */
/* We need to make sure that first is still the first entry on the */
/* list. Otherwise it's possible that a reinsertion of it was */
/* already started before we added the black list entry. */
if (AO_EXPECT_FALSE(first != AO_load(list))) {
AO_store_release(a->AO_stack_bl+i, 0);
goto retry;
}
first_ptr = AO_REAL_NEXT_PTR(first);
next = AO_load(first_ptr);
if (AO_EXPECT_FALSE(!AO_compare_and_swap_release(list, first, next))) {
AO_store_release(a->AO_stack_bl+i, 0);
goto retry;
}
assert(*list != first);
/* Since we never insert an entry on the black list, this cannot have */
/* succeeded unless first remained on the list while we were running. */
/* Thus its next link cannot have changed out from under us, and we */
/* removed exactly one entry and preserved the rest of the list. */
/* Note that it is quite possible that an additional entry was */
/* inserted and removed while we were running; this is OK since the */
/* part of the list following first must have remained unchanged, and */
/* first must again have been at the head of the list when the */
/* compare_and_swap succeeded. */
AO_store_release(a->AO_stack_bl+i, 0);
return first_ptr;
}
