glibc/nptl/DESIGN-barrier.txt

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Barriers pseudocode
===================
int pthread_barrier_wait(barrier_t *barrier);
struct barrier_t {
unsigned int lock:
- internal mutex
unsigned int left;
- current barrier count, # of threads still needed.
unsigned int init_count;
- number of threads needed for the barrier to continue.
unsigned int curr_event;
- generation count
}
pthread_barrier_wait(barrier_t *barrier)
{
unsigned int event;
result = 0;
lll_lock(barrier->lock);
if (!--barrier->left) {
barrier->curr_event++;
futex_wake(&barrier->curr_event, INT_MAX)
result = BARRIER_SERIAL_THREAD;
} else {
event = barrier->curr_event;
lll_unlock(barrier->lock);
do {
futex_wait(&barrier->curr_event, event)
} while (event == barrier->curr_event);
}
if (atomic_increment_val (barrier->left) == barrier->init_count)
lll_unlock(barrier->lock);
return result;
}