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1 files changed, 480 insertions, 0 deletions

diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/ConcurrentLinkedQueue.java b/libjava/classpath/external/jsr166/java/util/concurrent/ConcurrentLinkedQueue.java
new file mode 100644
index 000000000..000f4a4c9
--- /dev/null
+++ b/libjava/classpath/external/jsr166/java/util/concurrent/ConcurrentLinkedQueue.java
@@ -0,0 +1,480 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+import java.util.*;
+import java.util.concurrent.atomic.*;
+
+
+/**
+ * An unbounded thread-safe {@linkplain Queue queue} based on linked nodes.
+ * This queue orders elements FIFO (first-in-first-out).
+ * The <em>head</em> of the queue is that element that has been on the
+ * queue the longest time.
+ * The <em>tail</em> of the queue is that element that has been on the
+ * queue the shortest time. New elements
+ * are inserted at the tail of the queue, and the queue retrieval
+ * operations obtain elements at the head of the queue.
+ * A <tt>ConcurrentLinkedQueue</tt> is an appropriate choice when
+ * many threads will share access to a common collection.
+ * This queue does not permit <tt>null</tt> elements.
+ *
+ * <p>This implementation employs an efficient &quot;wait-free&quot;
+ * algorithm based on one described in <a
+ * href="http://www.cs.rochester.edu/u/michael/PODC96.html"> Simple,
+ * Fast, and Practical Non-Blocking and Blocking Concurrent Queue
+ * Algorithms</a> by Maged M. Michael and Michael L. Scott.
+ *
+ * <p>Beware that, unlike in most collections, the <tt>size</tt> method
+ * is <em>NOT</em> a constant-time operation. Because of the
+ * asynchronous nature of these queues, determining the current number
+ * of elements requires a traversal of the elements.
+ *
+ * <p>This class and its iterator implement all of the
+ * <em>optional</em> methods of the {@link Collection} and {@link
+ * Iterator} interfaces.
+ *
+ * <p>Memory consistency effects: As with other concurrent
+ * collections, actions in a thread prior to placing an object into a
+ * {@code ConcurrentLinkedQueue}
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * actions subsequent to the access or removal of that element from
+ * the {@code ConcurrentLinkedQueue} in another thread.
+ *
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
+ * Java Collections Framework</a>.
+ *
+ * @since 1.5
+ * @author Doug Lea
+ * @param <E> the type of elements held in this collection
+ *
+ */
+public class ConcurrentLinkedQueue<E> extends AbstractQueue<E>
+        implements Queue<E>, java.io.Serializable {
+    private static final long serialVersionUID = 196745693267521676L;
+
+    /*
+     * This is a straight adaptation of Michael & Scott algorithm.
+     * For explanation, read the paper.  The only (minor) algorithmic
+     * difference is that this version supports lazy deletion of
+     * internal nodes (method remove(Object)) -- remove CAS'es item
+     * fields to null. The normal queue operations unlink but then
+     * pass over nodes with null item fields. Similarly, iteration
+     * methods ignore those with nulls.
+     *
+     * Also note that like most non-blocking algorithms in this
+     * package, this implementation relies on the fact that in garbage
+     * collected systems, there is no possibility of ABA problems due
+     * to recycled nodes, so there is no need to use "counted
+     * pointers" or related techniques seen in versions used in
+     * non-GC'ed settings.
+     */
+
+    private static class Node<E> {
+        private volatile E item;
+        private volatile Node<E> next;
+
+        private static final
+            AtomicReferenceFieldUpdater<Node, Node>
+            nextUpdater =
+            AtomicReferenceFieldUpdater.newUpdater
+            (Node.class, Node.class, "next");
+        private static final
+            AtomicReferenceFieldUpdater<Node, Object>
+            itemUpdater =
+            AtomicReferenceFieldUpdater.newUpdater
+            (Node.class, Object.class, "item");
+
+        Node(E x) { item = x; }
+
+        Node(E x, Node<E> n) { item = x; next = n; }
+
+        E getItem() {
+            return item;
+        }
+
+        boolean casItem(E cmp, E val) {
+            return itemUpdater.compareAndSet(this, cmp, val);
+        }
+
+        void setItem(E val) {
+            itemUpdater.set(this, val);
+        }
+
+        Node<E> getNext() {
+            return next;
+        }
+
+        boolean casNext(Node<E> cmp, Node<E> val) {
+            return nextUpdater.compareAndSet(this, cmp, val);
+        }
+
+        void setNext(Node<E> val) {
+            nextUpdater.set(this, val);
+        }
+
+    }
+
+    private static final
+        AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
+        tailUpdater =
+        AtomicReferenceFieldUpdater.newUpdater
+        (ConcurrentLinkedQueue.class, Node.class, "tail");
+    private static final
+        AtomicReferenceFieldUpdater<ConcurrentLinkedQueue, Node>
+        headUpdater =
+        AtomicReferenceFieldUpdater.newUpdater
+        (ConcurrentLinkedQueue.class,  Node.class, "head");
+
+    private boolean casTail(Node<E> cmp, Node<E> val) {
+        return tailUpdater.compareAndSet(this, cmp, val);
+    }
+
+    private boolean casHead(Node<E> cmp, Node<E> val) {
+        return headUpdater.compareAndSet(this, cmp, val);
+    }
+
+
+    /**
+     * Pointer to header node, initialized to a dummy node.  The first
+     * actual node is at head.getNext().
+     */
+    private transient volatile Node<E> head = new Node<E>(null, null);
+
+    /** Pointer to last node on list **/
+    private transient volatile Node<E> tail = head;
+
+
+    /**
+     * Creates a <tt>ConcurrentLinkedQueue</tt> that is initially empty.
+     */
+    public ConcurrentLinkedQueue() {}
+
+    /**
+     * Creates a <tt>ConcurrentLinkedQueue</tt>
+     * initially containing the elements of the given collection,
+     * added in traversal order of the collection's iterator.
+     * @param c the collection of elements to initially contain
+     * @throws NullPointerException if the specified collection or any
+     *         of its elements are null
+     */
+    public ConcurrentLinkedQueue(Collection<? extends E> c) {
+        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
+            add(it.next());
+    }
+
+    // Have to override just to update the javadoc
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     *
+     * @return <tt>true</tt> (as specified by {@link Collection#add})
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean add(E e) {
+        return offer(e);
+    }
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     *
+     * @return <tt>true</tt> (as specified by {@link Queue#offer})
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean offer(E e) {
+        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 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,
+                }
+            }
+        }
+    }
+
+    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);
+                }
+            }
+        }
+    }
+
+    /**
+     * 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.)
+     */
+    Node<E> first() {
+        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);
+                }
+            }
+        }
+    }
+
+
+    /**
+     * Returns <tt>true</tt> if this queue contains no elements.
+     *
+     * @return <tt>true</tt> if this queue contains no elements
+     */
+    public boolean isEmpty() {
+        return first() == null;
+    }
+
+    /**
+     * Returns the number of elements in this queue.  If this queue
+     * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
+     * <tt>Integer.MAX_VALUE</tt>.
+     *
+     * <p>Beware that, unlike in most collections, this method is
+     * <em>NOT</em> a constant-time operation. Because of the
+     * asynchronous nature of these queues, determining the current
+     * number of elements requires an O(n) traversal.
+     *
+     * @return the number of elements in this queue
+     */
+    public int size() {
+        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;
+    }
+
+    /**
+     * Returns <tt>true</tt> if this queue contains the specified element.
+     * More formally, returns <tt>true</tt> if and only if this queue contains
+     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
+     *
+     * @param o object to be checked for containment in this queue
+     * @return <tt>true</tt> if this queue contains the specified element
+     */
+    public boolean contains(Object o) {
+        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;
+    }
+
+    /**
+     * Removes a single instance of the specified element from this queue,
+     * if it is present.  More formally, removes an element <tt>e</tt> such
+     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
+     * elements.
+     * Returns <tt>true</tt> if this queue contained the specified element
+     * (or equivalently, if this queue changed as a result of the call).
+     *
+     * @param o element to be removed from this queue, if present
+     * @return <tt>true</tt> if this queue changed as a result of the call
+     */
+    public boolean remove(Object o) {
+        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;
+    }
+
+    /**
+     * 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 an iterator over the elements in this queue in proper sequence
+     */
+    public Iterator<E> iterator() {
+        return new Itr();
+    }
+
+    private class Itr implements Iterator<E> {
+        /**
+         * Next node to return item for.
+         */
+        private Node<E> nextNode;
+
+        /**
+         * nextItem holds on to item fields because once we claim
+         * that an element exists in hasNext(), we must return it in
+         * the following next() call even if it was in the process of
+         * being removed when hasNext() was called.
+         */
+        private E nextItem;
+
+        /**
+         * Node of the last returned item, to support remove.
+         */
+        private Node<E> lastRet;
+
+        Itr() {
+            advance();
+        }
+
+        /**
+         * Moves to next valid node and returns item to return for
+         * next(), or null if no such.
+         */
+        private E advance() {
+            lastRet = nextNode;
+            E x = nextItem;
+
+            Node<E> p = (nextNode == null)? first() : nextNode.getNext();
+            for (;;) {
+                if (p == null) {
+                    nextNode = null;
+                    nextItem = null;
+                    return x;
+                }
+                E item = p.getItem();
+                if (item != null) {
+                    nextNode = p;
+                    nextItem = item;
+                    return x;
+                } else // skip over nulls
+                    p = p.getNext();
+            }
+        }
+
+        public boolean hasNext() {
+            return nextNode != null;
+        }
+
+        public E next() {
+            if (nextNode == null) throw new NoSuchElementException();
+            return advance();
+        }
+
+        public void remove() {
+            Node<E> l = lastRet;
+            if (l == null) throw new IllegalStateException();
+            // rely on a future traversal to relink.
+            l.setItem(null);
+            lastRet = null;
+        }
+    }
+
+    /**
+     * Save the state to a stream (that is, serialize it).
+     *
+     * @serialData All of the elements (each an <tt>E</tt>) in
+     * the proper order, followed by a null
+     * @param s the stream
+     */
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+
+        // 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);
+    }
+
+    /**
+     * Reconstitute the Queue instance from a stream (that is,
+     * deserialize it).
+     * @param s the stream
+     */
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        // 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);
+        }
+    }
+
+}