void unregisterWaiter(Thread waiter) {
WaitNode prev = null;
Object current = state;
while (current != null) {
Object currentWaiter =
current.getClass() == WaitNode.class ? ((WaitNode) current).waiter : current;
Object next = current.getClass() == WaitNode.class ? ((WaitNode) current).next : null;
if (currentWaiter == waiter) {
// it is the item we are looking for, so lets try to remove it
if (prev == null) {
// it's the first item of the stack, so we need to change the head to the next
Object n = next == null ? VOID : next;
// if we manage to CAS we are done, else we need to restart
current = compareAndSetState(current, n) ? null : state;
} else {
// remove the current item (this is done by letting the prev.next point to the next
// instead of current)
prev.next = next;
// end the loop
current = null;
}
} else {
// it isn't the item we are looking for, so lets move on to the next
prev = current.getClass() == WaitNode.class ? (WaitNode) current : null;
current = next;
}
}
}
/**
* Registers a waiter (thread/ExecutionCallback) that gets notified when the future completes.
*
* @param waiter the waiter
* @param executor the {@link Executor} to use in case of an {@link ExecutionCallback}.
* @return VOID if the registration was a success, anything else but void is the response.
*/
private Object registerWaiter(Object waiter, Executor executor) {
WaitNode waitNode = null;
for (; ; ) {
final Object oldState = state;
if (isDone(oldState)) {
return oldState;
}
Object newState;
if (oldState == VOID && (executor == null || executor == defaultExecutor)) {
// nothing is syncing on this future, so instead of creating a WaitNode, we just try to cas
// the waiter
newState = waiter;
} else {
// something already has been registered for syncing, so we need to create a WaitNode
if (waitNode == null) {
waitNode = new WaitNode(waiter, executor);
}
waitNode.next = oldState;
newState = waitNode;
}
if (compareAndSetState(oldState, newState)) {
// we have successfully registered
return VOID;
}
}
}
protected WaitNode extract() {
if (head_ == null) return null;
else {
WaitNode w = head_;
head_ = w.next;
if (head_ == null) tail_ = null;
w.next = null;
return w;
}
}
protected void insert(WaitNode w) {
if (tail_ == null) head_ = tail_ = w;
else {
tail_.next = w;
tail_ = w;
}
}
