/** Unlinks s from the stack. */
void clean(SNode s) {
s.item = null; // forget item
s.waiter = null; // forget thread
/*
* At worst we may need to traverse entire stack to unlink
* s. If there are multiple concurrent calls to clean, we
* might not see s if another thread has already removed
* it. But we can stop when we see any node known to
* follow s. We use s.next unless it too is cancelled, in
* which case we try the node one past. We don't check any
* further because we don't want to doubly traverse just to
* find sentinel.
*/
SNode past = s.next;
if (past != null && past.isCancelled()) past = past.next;
// Absorb cancelled nodes at head
SNode p;
while ((p = head) != null && p != past && p.isCancelled()) casHead(p, p.next);
// Unsplice embedded nodes
while (p != null && p != past) {
SNode n = p.next;
if (n != null && n.isCancelled()) p.casNext(n, n.next);
else p = n;
}
}
