/* See sem_wait for an explanation of the algorithm. */
int
__new_sem_post (sem_t *sem)
{
struct new_sem *isem = (struct new_sem *) sem;
int private = isem->private;
#if __HAVE_64B_ATOMICS
/* Add a token to the semaphore. We use release MO to make sure that a
thread acquiring this token synchronizes with us and other threads that
added tokens before (the release sequence includes atomic RMW operations
by other threads). */
/* TODO Use atomic_fetch_add to make it scale better than a CAS loop? */
uint64_t d = atomic_load_relaxed (&isem->data);
do
{
if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)
{
__set_errno (EOVERFLOW);
return -1;
}
}
while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));
/* If there is any potentially blocked waiter, wake one of them. */
if ((d >> SEM_NWAITERS_SHIFT) > 0)
futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private);
#else
/* Add a token to the semaphore. Similar to 64b version. */
unsigned int v = atomic_load_relaxed (&isem->value);
do
{
if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)
{
__set_errno (EOVERFLOW);
return -1;
}
}
while (!atomic_compare_exchange_weak_release
(&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));
/* If there is any potentially blocked waiter, wake one of them. */
if ((v & SEM_NWAITERS_MASK) != 0)
futex_wake (&isem->value, 1, private);
#endif
return 0;
}
versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_34);