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|128,1,0) != -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}
112