#include "pthread_impl.h"
/*
* struct waiter
*
* Waiter objects have automatic storage on the waiting thread, and
* are used in building a linked list representing waiters currently
* waiting on the condition variable or a group of waiters woken
* together by a broadcast or signal; in the case of signal, this is a
* degenerate list of one member.
*
* Waiter lists attached to the condition variable itself are
* protected by the lock on the cv. Detached waiter lists are never
* modified again, but can only be traversed in reverse order, and are
* protected by the "barrier" locks in each node, which are unlocked
* in turn to control wake order.
*
* Since process-shared cond var semantics do not necessarily allow
* one thread to see another's automatic storage (they may be in
* different processes), the waiter list is not used for the
* process-shared case, but the structure is still used to store data
* needed by the cancellation cleanup handler.
*/
struct waiter {
struct waiter *prev, *next;
volatile int state, barrier;
volatile int *notify;
};
/* Self-synchronized-destruction-safe lock functions */
static inline void lock(volatile int *l)
{
if (a_cas(l, 0, 1)) {
a_cas(l, 1, 2);
do __wait(l, 0, 2, 1);
while (a_cas(l, 0, 2));
}
}
static inline void unlock(volatile int *l)
{
if (a_swap(l, 0)==2)
__wake(l, 1, 1);
}
static inline void unlock_requeue(volatile int *l, volatile int *r, int w)
{
a_store(l, 0);
if (w) __wake(l, 1, 1);
else __syscall(SYS_futex, l, FUTEX_REQUEUE|FUTEX_PRIVATE, 0, 1, r) != -ENOSYS
|| __syscall(SYS_futex, l, FUTEX_REQUEUE, 0, 1, r);
}
enum {
WAITING,
SIGNALED,
LEAVING,
};
int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restrict m, const struct timespec *restrict ts)
{
struct waiter node = { 0 };
int e, seq, clock = c->_c_clock, cs, shared=0, oldstate, tmp;
volatile int *fut;
if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
return EPERM;
if (ts && ts->tv_nsec >= 1000000000UL)
return EINVAL;
__pthread_testcancel();
if (c->_c_shared) {
shared = 1;
fut = &c->_c_seq;
seq = c->_c_seq;
a_inc(&c->_c_waiters);
} else {
lock(&c->_c_lock);
seq = node.barrier = 2;
fut = &node.barrier;
node.state = WAITING;
node.next = c->_c_head;
c->_c_head = &node;
if (!c->_c_tail) c->_c_tail = &node;
else node.next->prev = &node;
unlock(&c->_c_lock);
}
__pthread_mutex_unlock(m);
__pthread_setcancelstate(PTHREAD_CANCEL_MASKED, &cs);
if (cs == PTHREAD_CANCEL_DISABLE) __pthread_setcancelstate(cs, 0);
do e = __timedwait_cp(fut, seq, clock, ts, !shared);
while (*fut==seq && (!e || e==EINTR));
if (e == EINTR) e = 0;
if (shared) {
/* Suppress cancellation if a signal was potentially
* consumed; this is a legitimate form of spurious
* wake even if not. */
if (e == ECANCELED && c->_c_seq != seq) e = 0;
if (a_fetch_add(&c->_c_waiters, -1) == -0x7fffffff)
__wake(&c->_c_waiters, 1, 0);
oldstate = WAITING;
goto relock;
}
oldstate = a_cas(&node.state, WAITING, LEAVING);
if (oldstate == WAITING) {
/* Access to cv object is valid because this waiter was not
* yet signaled and a new signal/broadcast cannot return
* after seeing a LEAVING waiter without getting notified
* via the futex notify below. */
lock(&c->_c_lock);
if (c->_c_head == &node) c->_c_head = node.next;
else if (node.prev) node.prev->next = node.next;
if (c->_c_tail == &node) c->_c_tail = node.prev;
else if (node.next) node.next->prev = node.prev;
unlock(&c->_c_lock);
if (node.notify) {
if (a_fetch_add(node.notify, -1)==1)
__wake(node.notify, 1, 1);
}
} else {
/* Lock barrier first to control wake order. */
lock(&node.barrier);
}
relock:
/* Errors locking the mutex override any existing error or
* cancellation, since the caller must see them to know the
* state of the mutex. */
if ((tmp = pthread_mutex_lock(m))) e = tmp;
if (oldstate == WAITING) goto done;
if (!node.next && !(m->_m_type & 8))
a_inc(&m->_m_waiters);
/* Unlock the barrier that's holding back the next waiter, and
* either wake it or requeue it to the mutex. */
if (node.prev) {
int val = m->_m_lock;
if (val>0) a_cas(&m->_m_lock, val, val|0x80000000);
unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & (8|128));
} else if (!(m->_m_type & 8)) {
a_dec(&m->_m_waiters);
}
/* Since a signal was consumed, cancellation is not permitted. */
if (e == ECANCELED) e = 0;
done:
__pthread_setcancelstate(cs, 0);
if (e == ECANCELED) {
__pthread_testcancel();
__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
}
return e;
}
int __private_cond_signal(pthread_cond_t *c, int n)
{
struct waiter *p, *first=0;
volatile int ref = 0;
int cur;
lock(&c->_c_lock);
for (p=c->_c_tail; n && p; p=p->prev) {
if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
ref++;
p->notify = &ref;
} else {
n--;
if (!first) first=p;
}
}
/* Split the list, leaving any remainder on the cv. */
if (p) {
if (p->next) p->next->prev = 0;
p->next = 0;
} else {
c->_c_head = 0;
}
c->_c_tail = p;
unlock(&c->_c_lock);
/* Wait for any waiters in the LEAVING state to remove
* themselves from the list before returning or allowing
* signaled threads to proceed. */
while ((cur = ref)) __wait(&ref, 0, cur, 1);
/* Allow first signaled waiter, if any, to proceed. */
if (first) unlock(&first->barrier);
return 0;
}
weak_alias(__pthread_cond_timedwait, pthread_cond_timedwait);
