1#include "pthread_impl.h"
  2
  3static int pshared_barrier_wait(pthread_barrier_t *b)
  4{
  5	int limit = (b->_b_limit & INT_MAX) + 1;
  6	int ret = 0;
  7	int v, w;
  8
  9	if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD;
 10
 11	while ((v=a_cas(&b->_b_lock, 0, limit)))
 12		__wait(&b->_b_lock, &b->_b_waiters, v, 0);
 13
 14	/* Wait for <limit> threads to get to the barrier */
 15	if (++b->_b_count == limit) {
 16		a_store(&b->_b_count, 0);
 17		ret = PTHREAD_BARRIER_SERIAL_THREAD;
 18		if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
 19	} else {
 20		a_store(&b->_b_lock, 0);
 21		if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
 22		while ((v=b->_b_count)>0)
 23			__wait(&b->_b_count, &b->_b_waiters2, v, 0);
 24	}
 25
 26	__vm_lock();
 27
 28	/* Ensure all threads have a vm lock before proceeding */
 29	if (a_fetch_add(&b->_b_count, -1)==1-limit) {
 30		a_store(&b->_b_count, 0);
 31		if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
 32	} else {
 33		while ((v=b->_b_count))
 34			__wait(&b->_b_count, &b->_b_waiters2, v, 0);
 35	}
 36	
 37	/* Perform a recursive unlock suitable for self-sync'd destruction */
 38	do {
 39		v = b->_b_lock;
 40		w = b->_b_waiters;
 41	} while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v);
 42
 43	/* Wake a thread waiting to reuse or destroy the barrier */
 44	if (v==INT_MIN+1 || (v==1 && w))
 45		__wake(&b->_b_lock, 1, 0);
 46
 47	__vm_unlock();
 48
 49	return ret;
 50}
 51
 52struct instance
 53{
 54	volatile int count;
 55	volatile int last;
 56	volatile int waiters;
 57	volatile int finished;
 58};
 59
 60int pthread_barrier_wait(pthread_barrier_t *b)
 61{
 62	int limit = b->_b_limit;
 63	struct instance *inst;
 64
 65	/* Trivial case: count was set at 1 */
 66	if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
 67
 68	/* Process-shared barriers require a separate, inefficient wait */
 69	if (limit < 0) return pshared_barrier_wait(b);
 70
 71	/* Otherwise we need a lock on the barrier object */
 72	while (a_swap(&b->_b_lock, 1))
 73		__wait(&b->_b_lock, &b->_b_waiters, 1, 1);
 74	inst = b->_b_inst;
 75
 76	/* First thread to enter the barrier becomes the "instance owner" */
 77	if (!inst) {
 78		struct instance new_inst = { 0 };
 79		int spins = 200;
 80		b->_b_inst = inst = &new_inst;
 81		a_store(&b->_b_lock, 0);
 82		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
 83		while (spins-- && !inst->finished)
 84			a_spin();
 85		a_inc(&inst->finished);
 86		while (inst->finished == 1)
 87			__syscall(SYS_futex,&inst->finished,FUTEX_WAIT|FUTEX_PRIVATE,1,0) != -ENOSYS
 88			|| __syscall(SYS_futex,&inst->finished,FUTEX_WAIT,1,0);
 89		return PTHREAD_BARRIER_SERIAL_THREAD;
 90	}
 91
 92	/* Last thread to enter the barrier wakes all non-instance-owners */
 93	if (++inst->count == limit) {
 94		b->_b_inst = 0;
 95		a_store(&b->_b_lock, 0);
 96		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
 97		a_store(&inst->last, 1);
 98		if (inst->waiters)
 99			__wake(&inst->last, -1, 1);
100	} else {
101		a_store(&b->_b_lock, 0);
102		if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
103		__wait(&inst->last, &inst->waiters, 0, 1);
104	}
105
106	/* Last thread to exit the barrier wakes the instance owner */
107	if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
108		__wake(&inst->finished, 1, 1);
109
110	return 0;
111}