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#include "pthread_impl.h"
struct instance
{
int count;
int last;
int waiters;
int finished;
};
int pthread_barrier_wait(pthread_barrier_t *b)
{
int limit = b->_b_limit;
struct instance *inst;
/* Trivial case: count was set at 1 */
if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
/* Otherwise we need a lock on the barrier object */
while (a_swap(&b->_b_lock, 1))
__wait(&b->_b_lock, &b->_b_waiters, 1, 0);
inst = b->_b_inst;
/* First thread to enter the barrier becomes the "instance owner" */
if (!inst) {
struct instance new_inst = { 0 };
int spins = 10000;
b->_b_inst = inst = &new_inst;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
while (spins-- && !inst->finished)
a_spin();
a_inc(&inst->finished);
while (inst->finished == 1)
__syscall(SYS_futex, &inst->finished, FUTEX_WAIT,1,0);
return PTHREAD_BARRIER_SERIAL_THREAD;
}
/* Last thread to enter the barrier wakes all non-instance-owners */
if (++inst->count == limit) {
b->_b_inst = 0;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
a_store(&inst->last, 1);
if (inst->waiters)
__wake(&inst->last, -1, 0);
} else {
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
__wait(&inst->last, &inst->waiters, 0, 0);
}
/* Last thread to exit the barrier wakes the instance owner */
if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
__wake(&inst->finished, 1, 0);
return 0;
}
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