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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