[398] | 1 | #include "pthread_impl.h"
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| 2 |
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| 3 | void __pthread_testcancel(void);
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| 4 | int __pthread_mutex_lock(pthread_mutex_t *);
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| 5 | int __pthread_mutex_unlock(pthread_mutex_t *);
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| 6 | int __pthread_setcancelstate(int, int *);
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| 7 |
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| 8 | /*
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| 9 | * struct waiter
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| 10 | *
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| 11 | * Waiter objects have automatic storage on the waiting thread, and
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| 12 | * are used in building a linked list representing waiters currently
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| 13 | * waiting on the condition variable or a group of waiters woken
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| 14 | * together by a broadcast or signal; in the case of signal, this is a
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| 15 | * degenerate list of one member.
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| 16 | *
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| 17 | * Waiter lists attached to the condition variable itself are
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| 18 | * protected by the lock on the cv. Detached waiter lists are never
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| 19 | * modified again, but can only be traversed in reverse order, and are
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| 20 | * protected by the "barrier" locks in each node, which are unlocked
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| 21 | * in turn to control wake order.
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| 22 | *
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| 23 | * Since process-shared cond var semantics do not necessarily allow
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| 24 | * one thread to see another's automatic storage (they may be in
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| 25 | * different processes), the waiter list is not used for the
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| 26 | * process-shared case, but the structure is still used to store data
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| 27 | * needed by the cancellation cleanup handler.
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| 28 | */
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| 29 |
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| 30 | struct waiter {
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| 31 | struct waiter *prev, *next;
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| 32 | volatile int state, barrier;
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| 33 | volatile int *notify;
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| 34 | };
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| 35 |
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| 36 | /* Self-synchronized-destruction-safe lock functions */
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| 37 |
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| 38 | static inline void lock(volatile int *l)
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| 39 | {
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| 40 | if (a_cas(l, 0, 1)) {
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| 41 | a_cas(l, 1, 2);
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| 42 | do __wait(l, 0, 2, 1);
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| 43 | while (a_cas(l, 0, 2));
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| 44 | }
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| 45 | }
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| 46 |
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| 47 | static inline void unlock(volatile int *l)
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| 48 | {
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| 49 | if (a_swap(l, 0)==2)
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| 50 | __wake(l, 1, 1);
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| 51 | }
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| 52 |
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| 53 | static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
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| 54 | {
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| 55 | a_store(l, 0);
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| 56 | if (w) __wake(l, 1, 1);
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| 57 | else __syscall(SYS_futex, l, FUTEX_REQUEUE|FUTEX_PRIVATE, 0, 1, r) != -ENOSYS
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| 58 | || __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
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| 59 | }
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| 60 |
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| 61 | enum {
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| 62 | WAITING,
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| 63 | SIGNALED,
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| 64 | LEAVING,
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| 65 | };
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| 66 |
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| 67 | int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
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| 68 | {
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| 69 | struct waiter node = { 0 };
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| 70 | int e, seq, clock = c->_c_clock, cs, shared=0, oldstate, tmp;
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| 71 | volatile int *fut;
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| 72 |
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| 73 | if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
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| 74 | return EPERM;
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| 75 |
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| 76 | if (ts && ts->tv_nsec >= 1000000000UL)
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| 77 | return EINVAL;
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| 78 |
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| 79 | __pthread_testcancel();
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| 80 |
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| 81 | if (c->_c_shared) {
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| 82 | shared = 1;
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| 83 | fut = &c->_c_seq;
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| 84 | seq = c->_c_seq;
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| 85 | a_inc(&c->_c_waiters);
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| 86 | } else {
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| 87 | lock(&c->_c_lock);
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| 88 |
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| 89 | seq = node.barrier = 2;
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| 90 | fut = &node.barrier;
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| 91 | node.state = WAITING;
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| 92 | node.next = c->_c_head;
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| 93 | c->_c_head = &node;
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| 94 | if (!c->_c_tail) c->_c_tail = &node;
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| 95 | else node.next->prev = &node;
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| 96 |
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| 97 | unlock(&c->_c_lock);
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| 98 | }
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| 99 |
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| 100 | __pthread_mutex_unlock(m);
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| 101 |
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| 102 | __pthread_setcancelstate(PTHREAD_CANCEL_MASKED, &cs);
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| 103 | if (cs == PTHREAD_CANCEL_DISABLE) __pthread_setcancelstate(cs, 0);
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| 104 |
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| 105 | do e = __timedwait_cp(fut, seq, clock, ts, !shared);
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| 106 | while (*fut==seq && (!e || e==EINTR));
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| 107 | if (e == EINTR) e = 0;
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| 108 |
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| 109 | if (shared) {
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| 110 | /* Suppress cancellation if a signal was potentially
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| 111 | * consumed; this is a legitimate form of spurious
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| 112 | * wake even if not. */
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| 113 | if (e == ECANCELED && c->_c_seq != seq) e = 0;
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| 114 | if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
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| 115 | __wake(&c->_c_waiters, 1, 0);
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| 116 | oldstate = WAITING;
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| 117 | goto relock;
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| 118 | }
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| 119 |
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| 120 | oldstate = a_cas(&node.state, WAITING, LEAVING);
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| 121 |
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| 122 | if (oldstate == WAITING) {
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| 123 | /* Access to cv object is valid because this waiter was not
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| 124 | * yet signaled and a new signal/broadcast cannot return
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| 125 | * after seeing a LEAVING waiter without getting notified
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| 126 | * via the futex notify below. */
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| 127 |
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| 128 | lock(&c->_c_lock);
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| 129 |
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| 130 | if (c->_c_head == &node) c->_c_head = node.next;
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| 131 | else if (node.prev) node.prev->next = node.next;
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| 132 | if (c->_c_tail == &node) c->_c_tail = node.prev;
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| 133 | else if (node.next) node.next->prev = node.prev;
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| 134 |
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| 135 | unlock(&c->_c_lock);
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| 136 |
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| 137 | if (node.notify) {
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| 138 | if (a_fetch_add(node.notify, -1)==1)
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| 139 | __wake(node.notify, 1, 1);
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| 140 | }
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| 141 | } else {
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| 142 | /* Lock barrier first to control wake order. */
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| 143 | lock(&node.barrier);
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| 144 | }
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| 145 |
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| 146 | relock:
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| 147 | /* Errors locking the mutex override any existing error or
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| 148 | * cancellation, since the caller must see them to know the
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| 149 | * state of the mutex. */
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| 150 | if ((tmp = pthread_mutex_lock(m))) e = tmp;
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| 151 |
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| 152 | if (oldstate == WAITING) goto done;
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| 153 |
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| 154 | if (!node.next) a_inc(&m->_m_waiters);
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| 155 |
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| 156 | /* Unlock the barrier that's holding back the next waiter, and
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| 157 | * either wake it or requeue it to the mutex. */
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| 158 | if (node.prev)
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| 159 | unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
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| 160 | else
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| 161 | a_dec(&m->_m_waiters);
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| 162 |
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| 163 | /* Since a signal was consumed, cancellation is not permitted. */
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| 164 | if (e == ECANCELED) e = 0;
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| 165 |
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| 166 | done:
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| 167 | __pthread_setcancelstate(cs, 0);
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| 168 |
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| 169 | if (e == ECANCELED) {
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| 170 | __pthread_testcancel();
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| 171 | __pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
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| 172 | }
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| 173 |
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| 174 | return e;
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| 175 | }
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| 176 |
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| 177 | int __private_cond_signal(pthread_cond_t *c, int n)
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| 178 | {
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| 179 | struct waiter *p, *first=0;
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| 180 | volatile int ref = 0;
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| 181 | int cur;
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| 182 |
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| 183 | lock(&c->_c_lock);
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| 184 | for (p=c->_c_tail; n && p; p=p->prev) {
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| 185 | if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
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| 186 | ref++;
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| 187 | p->notify = &ref;
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| 188 | } else {
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| 189 | n--;
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| 190 | if (!first) first=p;
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| 191 | }
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| 192 | }
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| 193 | /* Split the list, leaving any remainder on the cv. */
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| 194 | if (p) {
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| 195 | if (p->next) p->next->prev = 0;
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| 196 | p->next = 0;
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| 197 | } else {
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| 198 | c->_c_head = 0;
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| 199 | }
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| 200 | c->_c_tail = p;
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| 201 | unlock(&c->_c_lock);
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| 202 |
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| 203 | /* Wait for any waiters in the LEAVING state to remove
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| 204 | * themselves from the list before returning or allowing
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| 205 | * signaled threads to proceed. */
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| 206 | while ((cur = ref)) __wait(&ref, 0, cur, 1);
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| 207 |
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| 208 | /* Allow first signaled waiter, if any, to proceed. */
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| 209 | if (first) unlock(&first->barrier);
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| 210 |
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| 211 | return 0;
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| 212 | }
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| 213 |
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| 214 | weak_alias(__pthread_cond_timedwait, pthread_cond_timedwait);
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