1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
| | #include "pthread_impl.h"
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();
/* 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();
return ret;
}
struct instance
{
volatile int count;
volatile int last;
volatile int waiters;
volatile 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;
/* Process-shared barriers require a separate, inefficient wait */
if (limit < 0) return pshared_barrier_wait(b);
/* 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 = 200;
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)
__futexcall(&inst->finished,FUTEX_WAIT|FUTEX_PRIVATE,1,0) != -ENOSYS
|| __futexcall(&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, 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);
}
/* 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;
}
|