1#include "pthread_impl.h"
2
3void __pthread_testcancel(void);
4int __pthread_mutex_lock(pthread_mutex_t *);
5int __pthread_mutex_unlock(pthread_mutex_t *);
6int __pthread_setcancelstate(int, int *);
7
8/*
9 * struct waiter
10 *
11 * Waiter objects have automatic storage on the waiting thread, and
12 * are used in building a linked list representing waiters currently
13 * waiting on the condition variable or a group of waiters woken
14 * together by a broadcast or signal; in the case of signal, this is a
15 * degenerate list of one member.
16 *
17 * Waiter lists attached to the condition variable itself are
18 * protected by the lock on the cv. Detached waiter lists are never
19 * modified again, but can only be traversed in reverse order, and are
20 * protected by the "barrier" locks in each node, which are unlocked
21 * in turn to control wake order.
22 *
23 * Since process-shared cond var semantics do not necessarily allow
24 * one thread to see another's automatic storage (they may be in
25 * different processes), the waiter list is not used for the
26 * process-shared case, but the structure is still used to store data
27 * needed by the cancellation cleanup handler.
28 */
29
30struct waiter {
31	struct waiter *prev, *next;
32	volatile int state, barrier;
33	volatile int *notify;
34};
35
36/* Self-synchronized-destruction-safe lock functions */
37
38static inline void lock(volatile int *l)
39{
40	if (a_cas(l, 0, 1)) {
41		a_cas(l, 1, 2);
42		do __wait(l, 0, 2, 1);
43		while (a_cas(l, 0, 2));
44	}
45}
46
47static inline void unlock(volatile int *l)
48{
49	if (a_swap(l, 0)==2)
50		__wake(l, 1, 1);
51}
52
53static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
54{
55	a_store(l, 0);
56	if (w) __wake(l, 1, 1);
57	else __syscall(SYS_futex, l, FUTEX_REQUEUE|128, 0, 1, r) != -ENOSYS
58		|| __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
59}
60
61enum {
62	WAITING,
63	SIGNALED,
64	LEAVING,
65};
66
67int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
68{
69	struct waiter node = { 0 };
70	int e, seq, clock = c->_c_clock, cs, shared=0, oldstate, tmp;
71	volatile int *fut;
72
73	if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
74		return EPERM;
75
76	if (ts && ts->tv_nsec >= 1000000000UL)
77		return EINVAL;
78
79	__pthread_testcancel();
80
81	if (c->_c_shared) {
82		shared = 1;
83		fut = &c->_c_seq;
84		seq = c->_c_seq;
85		a_inc(&c->_c_waiters);
86	} else {
87		lock(&c->_c_lock);
88
89		seq = node.barrier = 2;
90		fut = &node.barrier;
91		node.state = WAITING;
92		node.next = c->_c_head;
93		c->_c_head = &node;
94		if (!c->_c_tail) c->_c_tail = &node;
95		else node.next->prev = &node;
96
97		unlock(&c->_c_lock);
98	}
99
100	__pthread_mutex_unlock(m);
101
102	__pthread_setcancelstate(PTHREAD_CANCEL_MASKED, &cs);
103	if (cs == PTHREAD_CANCEL_DISABLE) __pthread_setcancelstate(cs, 0);
104
105	do e = __timedwait_cp(fut, seq, clock, ts, !shared);
106	while (*fut==seq && (!e || e==EINTR));
107	if (e == EINTR) e = 0;
108
109	if (shared) {
110		/* Suppress cancellation if a signal was potentially
111		 * consumed; this is a legitimate form of spurious
112		 * wake even if not. */
113		if (e == ECANCELED && c->_c_seq != seq) e = 0;
114		if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
115			__wake(&c->_c_waiters, 1, 0);
116		oldstate = WAITING;
117		goto relock;
118	}
119
120	oldstate = a_cas(&node.state, WAITING, LEAVING);
121
122	if (oldstate == WAITING) {
123		/* Access to cv object is valid because this waiter was not
124		 * yet signaled and a new signal/broadcast cannot return
125		 * after seeing a LEAVING waiter without getting notified
126		 * via the futex notify below. */
127
128		lock(&c->_c_lock);
129
130		if (c->_c_head == &node) c->_c_head = node.next;
131		else if (node.prev) node.prev->next = node.next;
132		if (c->_c_tail == &node) c->_c_tail = node.prev;
133		else if (node.next) node.next->prev = node.prev;
134
135		unlock(&c->_c_lock);
136
137		if (node.notify) {
138			if (a_fetch_add(node.notify, -1)==1)
139				__wake(node.notify, 1, 1);
140		}
141	} else {
142		/* Lock barrier first to control wake order. */
143		lock(&node.barrier);
144	}
145
146relock:
147	/* Errors locking the mutex override any existing error or
148	 * cancellation, since the caller must see them to know the
149	 * state of the mutex. */
150	if ((tmp = pthread_mutex_lock(m))) e = tmp;
151
152	if (oldstate == WAITING) goto done;
153
154	if (!node.next) a_inc(&m->_m_waiters);
155
156	/* Unlock the barrier that's holding back the next waiter, and
157	 * either wake it or requeue it to the mutex. */
158	if (node.prev)
159		unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
160	else
161		a_dec(&m->_m_waiters);
162
163	/* Since a signal was consumed, cancellation is not permitted. */
164	if (e == ECANCELED) e = 0;
165
166done:
167	__pthread_setcancelstate(cs, 0);
168
169	if (e == ECANCELED) {
170		__pthread_testcancel();
171		__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
172	}
173
174	return e;
175}
176
177int __private_cond_signal(pthread_cond_t *c, int n)
178{
179	struct waiter *p, *first=0;
180	volatile int ref = 0;
181	int cur;
182
183	lock(&c->_c_lock);
184	for (p=c->_c_tail; n && p; p=p->prev) {
185		if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
186			ref++;
187			p->notify = &ref;
188		} else {
189			n--;
190			if (!first) first=p;
191		}
192	}
193	/* Split the list, leaving any remainder on the cv. */
194	if (p) {
195		if (p->next) p->next->prev = 0;
196		p->next = 0;
197	} else {
198		c->_c_head = 0;
199	}
200	c->_c_tail = p;
201	unlock(&c->_c_lock);
202
203	/* Wait for any waiters in the LEAVING state to remove
204	 * themselves from the list before returning or allowing
205	 * signaled threads to proceed. */
206	while ((cur = ref)) __wait(&ref, 0, cur, 1);
207
208	/* Allow first signaled waiter, if any, to proceed. */
209	if (first) unlock(&first->barrier);
210
211	return 0;
212}
213
214weak_alias(__pthread_cond_timedwait, pthread_cond_timedwait);
215