Add a "fork" of musl as //fusl.

fusl/src/thread/pthread_cond_timedwait.c

+#include "pthread_impl.h"
+
+void __pthread_testcancel(void);
+int __pthread_mutex_lock(pthread_mutex_t *);
+int __pthread_mutex_unlock(pthread_mutex_t *);
+int __pthread_setcancelstate(int, int *);
+
+/*
+ * 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|128, 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) 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)
+                unlock_requeue(&node.prev->barrier, &m->_m_lock, m->_m_type & 128);
+        else
+                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);