/** Tries to artificially match a data node -- used by remove. */
final boolean tryMatchData() {
// assert isData;
Object x = item;
if (x != null && x != this && casItem(x, null)) {
Strand.unpark(waiter, this);
return true;
}
return false;
}
private Object tryMatch(SelectActionImpl sa, Message e, boolean haveData) {
boolean closed = isSendClosed(); // must be read before trying to match so as not to miss puts
for (Node h = head, p = h; p != null; ) { // find & match first node
boolean isData = p.isData;
Object item = p.item;
if (item != p && (item != null) == isData) { // unmatched
if (isData == haveData) // can't match
break;
// avoid deadlock by orderdering lease acquisition:
// if p requires a lease and is of lower hashCode than sa, we return sa's lease, acquire
// p's, and then reacquire sa's.
SelectActionImpl sa2 = p.sa;
boolean leasedp;
if (sa != null && sa2 != null && sa2.selector().id < sa.selector().id) {
sa.returnLease();
leasedp = sa2.lease();
if (!sa.lease()) {
if (leasedp) sa2.returnLease();
return LOST;
}
} else leasedp = p.lease();
if (leasedp) {
if (p.casItem(item, e)) { // match
p.won();
for (Node q = p; q != h; ) {
Node n = q.next; // update by 2 unless singleton
if (head == h && casHead(h, n == null ? q : n)) {
h.forgetNext();
break;
} // advance and retry
if ((h = head) == null || (q = h.next) == null || !q.isMatched())
break; // unless slack < 2
}
Strand.unpark(p.waiter, this);
return item;
} else p.returnLease();
}
}
Node n = p.next;
p = (p != n) ? n : (h = head); // Use head if p offlist
}
if (closed) {
assert !haveData;
setReceiveClosed();
return CHANNEL_CLOSED;
}
return NO_MATCH;
}
private void signalWaitersOnClose() {
for (Node p = head; p != null; ) {
if (!p.isMatched()) {
if (!p.isData) {
if (p.casItem(null, CHANNEL_CLOSED)) // match waiting requesters with CHANNEL_CLOSED
Strand.unpark(p.waiter, this); // ... and wake 'em up
} else p.tryMatchData();
}
Node n = p.next;
if (n != p) p = n;
else p = head;
}
}