1 #include "pthread_impl.h"
6 * Waiter objects have automatic storage on the waiting thread, and
7 * are used in building a linked list representing waiters currently
8 * waiting on the condition variable or a group of waiters woken
9 * together by a broadcast or signal; in the case of signal, this is a
10 * degenerate list of one member.
12 * Waiter lists attached to the condition variable itself are
13 * protected by the lock on the cv. Detached waiter lists are never
14 * modified again, but can only be traversed in reverse order, and are
15 * protected by the "barrier" locks in each node, which are unlocked
16 * in turn to control wake order.
18 * Since process-shared cond var semantics do not necessarily allow
19 * one thread to see another's automatic storage (they may be in
20 * different processes), the waiter list is not used for the
21 * process-shared case, but the structure is still used to store data
22 * needed by the cancellation cleanup handler.
26 struct waiter *prev, *next;
27 int state, barrier, mutex_ret;
29 pthread_mutex_t *mutex;
34 /* Self-synchronized-destruction-safe lock functions */
36 static inline void lock(volatile int *l)
40 do __wait(l, 0, 2, 1);
41 while (a_cas(l, 0, 2));
45 static inline void unlock(volatile int *l)
51 static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
54 if (w) __wake(l, 1, 1);
55 else __syscall(SYS_futex, l, FUTEX_REQUEUE|128, 0, 1, r) != -EINVAL
56 || __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
65 static void unwait(void *arg)
67 struct waiter *node = arg;
70 pthread_cond_t *c = node->cond;
71 pthread_mutex_t *m = node->mutex;
72 if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
73 __wake(&c->_c_waiters, 1, 0);
74 node->mutex_ret = pthread_mutex_lock(m);
78 int oldstate = a_cas(&node->state, WAITING, LEAVING);
80 if (oldstate == WAITING) {
81 /* Access to cv object is valid because this waiter was not
82 * yet signaled and a new signal/broadcast cannot return
83 * after seeing a LEAVING waiter without getting notified
84 * via the futex notify below. */
86 pthread_cond_t *c = node->cond;
89 if (c->_c_head == node) c->_c_head = node->next;
90 else if (node->prev) node->prev->next = node->next;
91 if (c->_c_tail == node) c->_c_tail = node->prev;
92 else if (node->next) node->next->prev = node->prev;
97 if (a_fetch_add(node->notify, -1)==1)
98 __wake(node->notify, 1, 1);
101 /* Lock barrier first to control wake order. */
102 lock(&node->barrier);
105 node->mutex_ret = pthread_mutex_lock(node->mutex);
107 if (oldstate == WAITING) return;
109 if (!node->next) a_inc(&node->mutex->_m_waiters);
111 /* Unlock the barrier that's holding back the next waiter, and
112 * either wake it or requeue it to the mutex. */
114 unlock_requeue(&node->prev->barrier,
115 &node->mutex->_m_lock,
116 node->mutex->_m_type & 128);
118 a_dec(&node->mutex->_m_waiters);
122 int pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
124 struct waiter node = { .cond = c, .mutex = m };
125 int e, seq, *fut, clock = c->_c_clock;
127 if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
130 if (ts && ts->tv_nsec >= 1000000000UL)
133 pthread_testcancel();
139 a_inc(&c->_c_waiters);
143 seq = node.barrier = 2;
145 node.state = WAITING;
146 node.next = c->_c_head;
148 if (!c->_c_tail) c->_c_tail = &node;
149 else node.next->prev = &node;
154 pthread_mutex_unlock(m);
156 do e = __timedwait(fut, seq, clock, ts, unwait, &node, !node.shared);
157 while (*fut==seq && (!e || e==EINTR));
158 if (e == EINTR) e = 0;
162 return node.mutex_ret ? node.mutex_ret : e;
165 int __private_cond_signal(pthread_cond_t *c, int n)
167 struct waiter *p, *first=0;
171 for (p=c->_c_tail; n && p; p=p->prev) {
172 if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
180 /* Split the list, leaving any remainder on the cv. */
182 if (p->next) p->next->prev = 0;
190 /* Wait for any waiters in the LEAVING state to remove
191 * themselves from the list before returning or allowing
192 * signaled threads to proceed. */
193 while ((cur = ref)) __wait(&ref, 0, cur, 1);
195 /* Allow first signaled waiter, if any, to proceed. */
196 if (first) unlock(&first->barrier);