| Methods Summary |
|---|
| public boolean | add(E e)Inserts the specified element at the tail of this queue.
return offer(e);
|
| private boolean | casHead(java.util.concurrent.ConcurrentLinkedQueue$Node cmp, java.util.concurrent.ConcurrentLinkedQueue$Node val)
return headUpdater.compareAndSet(this, cmp, val);
|
| private boolean | casTail(java.util.concurrent.ConcurrentLinkedQueue$Node cmp, java.util.concurrent.ConcurrentLinkedQueue$Node val)
return tailUpdater.compareAndSet(this, cmp, val);
|
| public boolean | contains(java.lang.Object o)Returns true if this queue contains the specified element.
More formally, returns true if and only if this queue contains
at least one element e such that o.equals(e).
if (o == null) return false;
for (Node<E> p = first(); p != null; p = p.getNext()) {
E item = p.getItem();
if (item != null &&
o.equals(item))
return true;
}
return false;
|
| java.util.concurrent.ConcurrentLinkedQueue$Node | first()Returns the first actual (non-header) node on list. This is yet
another variant of poll/peek; here returning out the first
node, not element (so we cannot collapse with peek() without
introducing race.)
for (;;) {
Node<E> h = head;
Node<E> t = tail;
Node<E> first = h.getNext();
if (h == head) {
if (h == t) {
if (first == null)
return null;
else
casTail(t, first);
} else {
if (first.getItem() != null)
return first;
else // remove deleted node and continue
casHead(h, first);
}
}
}
|
| public boolean | isEmpty()Returns true if this queue contains no elements.
return first() == null;
|
| public java.util.Iterator | iterator()Returns an iterator over the elements in this queue in proper sequence.
The returned iterator is a "weakly consistent" iterator that
will never throw {@link ConcurrentModificationException},
and guarantees to traverse elements as they existed upon
construction of the iterator, and may (but is not guaranteed to)
reflect any modifications subsequent to construction.
return new Itr();
|
| public boolean | offer(E e)Inserts the specified element at the tail of this queue.
if (e == null) throw new NullPointerException();
Node<E> n = new Node<E>(e, null);
for (;;) {
Node<E> t = tail;
Node<E> s = t.getNext();
if (t == tail) {
if (s == null) {
if (t.casNext(s, n)) {
casTail(t, n);
return true;
}
} else {
casTail(t, s);
}
}
}
|
| public E | peek() // same as poll except don't remove item
for (;;) {
Node<E> h = head;
Node<E> t = tail;
Node<E> first = h.getNext();
if (h == head) {
if (h == t) {
if (first == null)
return null;
else
casTail(t, first);
} else {
E item = first.getItem();
if (item != null)
return item;
else // remove deleted node and continue
casHead(h, first);
}
}
}
|
| public E | poll()
for (;;) {
Node<E> h = head;
Node<E> t = tail;
Node<E> first = h.getNext();
if (h == head) {
if (h == t) {
if (first == null)
return null;
else
casTail(t, first);
} else if (casHead(h, first)) {
E item = first.getItem();
if (item != null) {
first.setItem(null);
return item;
}
// else skip over deleted item, continue loop,
}
}
}
|
| private void | readObject(java.io.ObjectInputStream s)Reconstitute the Queue instance from a stream (that is,
deserialize it).
// Read in capacity, and any hidden stuff
s.defaultReadObject();
head = new Node<E>(null, null);
tail = head;
// Read in all elements and place in queue
for (;;) {
E item = (E)s.readObject();
if (item == null)
break;
else
offer(item);
}
|
| public boolean | remove(java.lang.Object o)Removes a single instance of the specified element from this queue,
if it is present. More formally, removes an element e such
that o.equals(e), if this queue contains one or more such
elements.
Returns true if this queue contained the specified element
(or equivalently, if this queue changed as a result of the call).
if (o == null) return false;
for (Node<E> p = first(); p != null; p = p.getNext()) {
E item = p.getItem();
if (item != null &&
o.equals(item) &&
p.casItem(item, null))
return true;
}
return false;
|
| public int | size()Returns the number of elements in this queue. If this queue
contains more than Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Beware that, unlike in most collections, this method is
NOT a constant-time operation. Because of the
asynchronous nature of these queues, determining the current
number of elements requires an O(n) traversal.
int count = 0;
for (Node<E> p = first(); p != null; p = p.getNext()) {
if (p.getItem() != null) {
// Collections.size() spec says to max out
if (++count == Integer.MAX_VALUE)
break;
}
}
return count;
|
| public java.lang.Object[] | toArray()Returns an array containing all of the elements in this queue, in
proper sequence.
The returned array will be "safe" in that no references to it are
maintained by this queue. (In other words, this method must allocate
a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based
APIs.
// Use ArrayList to deal with resizing.
ArrayList<E> al = new ArrayList<E>();
for (Node<E> p = first(); p != null; p = p.getNext()) {
E item = p.getItem();
if (item != null)
al.add(item);
}
return al.toArray();
|
| public T[] | toArray(T[] a)Returns an array containing all of the elements in this queue, in
proper sequence; the runtime type of the returned array is that of
the specified array. If the queue fits in the specified array, it
is returned therein. Otherwise, a new array is allocated with the
runtime type of the specified array and the size of this queue.
If this queue fits in the specified array with room to spare
(i.e., the array has more elements than this queue), the element in
the array immediately following the end of the queue is set to
null.
Like the {@link #toArray()} method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a queue known to contain only strings.
The following code can be used to dump the queue into a newly
allocated array of String:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to
toArray().
// try to use sent-in array
int k = 0;
Node<E> p;
for (p = first(); p != null && k < a.length; p = p.getNext()) {
E item = p.getItem();
if (item != null)
a[k++] = (T)item;
}
if (p == null) {
if (k < a.length)
a[k] = null;
return a;
}
// If won't fit, use ArrayList version
ArrayList<E> al = new ArrayList<E>();
for (Node<E> q = first(); q != null; q = q.getNext()) {
E item = q.getItem();
if (item != null)
al.add(item);
}
return (T[])al.toArray(a);
|
| private void | writeObject(java.io.ObjectOutputStream s)Save the state to a stream (that is, serialize it).
// Write out any hidden stuff
s.defaultWriteObject();
// Write out all elements in the proper order.
for (Node<E> p = first(); p != null; p = p.getNext()) {
Object item = p.getItem();
if (item != null)
s.writeObject(item);
}
// Use trailing null as sentinel
s.writeObject(null);
|
