#include "pthread_impl.h"
+void __vm_lock_impl(int);
+void __vm_unlock_impl(void);
+
+static int pshared_barrier_wait(pthread_barrier_t *b)
+{
+ int limit = (b->_b_limit & INT_MAX) + 1;
+ int ret = 0;
+ int v, w;
+
+ if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD;
+
+ while ((v=a_cas(&b->_b_lock, 0, limit)))
+ __wait(&b->_b_lock, &b->_b_waiters, v, 0);
+
+ /* Wait for <limit> threads to get to the barrier */
+ if (++b->_b_count == limit) {
+ a_store(&b->_b_count, 0);
+ ret = PTHREAD_BARRIER_SERIAL_THREAD;
+ if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
+ } else {
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ while ((v=b->_b_count)>0)
+ __wait(&b->_b_count, &b->_b_waiters2, v, 0);
+ }
+
+ __vm_lock_impl(+1);
+
+ /* Ensure all threads have a vm lock before proceeding */
+ if (a_fetch_add(&b->_b_count, -1)==1-limit) {
+ a_store(&b->_b_count, 0);
+ if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
+ } else {
+ while ((v=b->_b_count))
+ __wait(&b->_b_count, &b->_b_waiters2, v, 0);
+ }
+
+ /* Perform a recursive unlock suitable for self-sync'd destruction */
+ do {
+ v = b->_b_lock;
+ w = b->_b_waiters;
+ } while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v);
+
+ /* Wake a thread waiting to reuse or destroy the barrier */
+ if (v==INT_MIN+1 || (v==1 && w))
+ __wake(&b->_b_lock, 1, 0);
+
+ __vm_unlock_impl();
+
+ return ret;
+}
+
+struct instance
+{
+ int count;
+ int last;
+ int waiters;
+ int finished;
+};
+
int pthread_barrier_wait(pthread_barrier_t *b)
{
- int cur;
+ int limit = b->_b_limit;
+ struct instance *inst;
/* Trivial case: count was set at 1 */
- if (!b->__limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+ if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
- /* Wait for anyone still suspended at previous use of barrier */
- while ((cur=b->__left))
- __wait(&b->__left, &b->__waiters, cur, 0);
+ /* Process-shared barriers require a separate, inefficient wait */
+ if (limit < 0) return pshared_barrier_wait(b);
- /* If we are the last to reach barrier, reset it and wake others */
- if (a_fetch_add(&b->__count, 1) == b->__limit) {
- b->__left = b->__limit;
- b->__count = 0;
- __wake(&b->__count, -1, 0);
+ /* Otherwise we need a lock on the barrier object */
+ while (a_swap(&b->_b_lock, 1))
+ __wait(&b->_b_lock, &b->_b_waiters, 1, 1);
+ 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, 1);
+ 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;
}
- /* Wait for our peers to reach the barrier */
- while ((cur=b->__count))
- __wait(&b->__count, 0, cur, 0);
+ /* 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, 1);
+ a_store(&inst->last, 1);
+ if (inst->waiters)
+ __wake(&inst->last, -1, 1);
+ } else {
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
+ __wait(&inst->last, &inst->waiters, 0, 1);
+ }
- /* If we're the last to wake up and barrier is awaiting reuse */
- if (a_fetch_add(&b->__left, -1) == 1 && b->__waiters)
- __wake(&b->__left, -1, 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, 1);
return 0;
}