My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

Showing the changes to java/pkg/java/util/concurrent/LinkedBlockingQueue.java (1 of 18352 files). Show all

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	1	+/*
	2	+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	3	+ *
	4	+ * This code is free software; you can redistribute it and/or modify it
	5	+ * under the terms of the GNU General Public License version 2 only, as
	6	+ * published by the Free Software Foundation. Oracle designates this
	7	+ * particular file as subject to the "Classpath" exception as provided
	8	+ * by Oracle in the LICENSE file that accompanied this code.
	9	+ *
	10	+ * This code is distributed in the hope that it will be useful, but WITHOUT
	11	+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	12	+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	13	+ * version 2 for more details (a copy is included in the LICENSE file that
	14	+ * accompanied this code).
	15	+ *
	16	+ * You should have received a copy of the GNU General Public License version
	17	+ * 2 along with this work; if not, write to the Free Software Foundation,
	18	+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	19	+ *
	20	+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	21	+ * or visit www.oracle.com if you need additional information or have any
	22	+ * questions.
	23	+ */
	24	+
	25	+/*
	26	+ * This file is available under and governed by the GNU General Public
	27	+ * License version 2 only, as published by the Free Software Foundation.
	28	+ * However, the following notice accompanied the original version of this
	29	+ * file:
	30	+ *
	31	+ * Written by Doug Lea with assistance from members of JCP JSR-166
	32	+ * Expert Group and released to the public domain, as explained at
	33	+ * http://creativecommons.org/publicdomain/zero/1.0/
	34	+ */
	35	+
	36	+package java.util.concurrent;
	37	+
	38	+import java.util.concurrent.atomic.AtomicInteger;
	39	+import java.util.concurrent.locks.Condition;
	40	+import java.util.concurrent.locks.ReentrantLock;
	41	+import java.util.AbstractQueue;
	42	+import java.util.Collection;
	43	+import java.util.Iterator;
	44	+import java.util.NoSuchElementException;
	45	+
	46	+/**
	47	+ * An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
	48	+ * linked nodes.
	49	+ * This queue orders elements FIFO (first-in-first-out).
	50	+ * The <em>head</em> of the queue is that element that has been on the
	51	+ * queue the longest time.
	52	+ * The <em>tail</em> of the queue is that element that has been on the
	53	+ * queue the shortest time. New elements
	54	+ * are inserted at the tail of the queue, and the queue retrieval
	55	+ * operations obtain elements at the head of the queue.
	56	+ * Linked queues typically have higher throughput than array-based queues but
	57	+ * less predictable performance in most concurrent applications.
	58	+ *
	59	+ * <p> The optional capacity bound constructor argument serves as a
	60	+ * way to prevent excessive queue expansion. The capacity, if unspecified,
	61	+ * is equal to {@link Integer#MAX_VALUE}. Linked nodes are
	62	+ * dynamically created upon each insertion unless this would bring the
	63	+ * queue above capacity.
	64	+ *
	65	+ * <p>This class and its iterator implement all of the
	66	+ * <em>optional</em> methods of the {@link Collection} and {@link
	67	+ * Iterator} interfaces.
	68	+ *
	69	+ * <p>This class is a member of the
	70	+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
	71	+ * Java Collections Framework</a>.
	72	+ *
	73	+ * @since 1.5
	74	+ * @author Doug Lea
	75	+ * @param <E> the type of elements held in this collection
	76	+ *
	77	+ */
	78	+public class LinkedBlockingQueue<E> extends AbstractQueue<E>
	79	+ implements BlockingQueue<E>, java.io.Serializable {
	80	+ private static final long serialVersionUID = -6903933977591709194L;
	81	+
	82	+ /*
	83	+ * A variant of the "two lock queue" algorithm. The putLock gates
	84	+ * entry to put (and offer), and has an associated condition for
	85	+ * waiting puts. Similarly for the takeLock. The "count" field
	86	+ * that they both rely on is maintained as an atomic to avoid
	87	+ * needing to get both locks in most cases. Also, to minimize need
	88	+ * for puts to get takeLock and vice-versa, cascading notifies are
	89	+ * used. When a put notices that it has enabled at least one take,
	90	+ * it signals taker. That taker in turn signals others if more
	91	+ * items have been entered since the signal. And symmetrically for
	92	+ * takes signalling puts. Operations such as remove(Object) and
	93	+ * iterators acquire both locks.
	94	+ *
	95	+ * Visibility between writers and readers is provided as follows:
	96	+ *
	97	+ * Whenever an element is enqueued, the putLock is acquired and
	98	+ * count updated. A subsequent reader guarantees visibility to the
	99	+ * enqueued Node by either acquiring the putLock (via fullyLock)
	100	+ * or by acquiring the takeLock, and then reading n = count.get();
	101	+ * this gives visibility to the first n items.
	102	+ *
	103	+ * To implement weakly consistent iterators, it appears we need to
	104	+ * keep all Nodes GC-reachable from a predecessor dequeued Node.
	105	+ * That would cause two problems:
	106	+ * - allow a rogue Iterator to cause unbounded memory retention
	107	+ * - cause cross-generational linking of old Nodes to new Nodes if
	108	+ * a Node was tenured while live, which generational GCs have a
	109	+ * hard time dealing with, causing repeated major collections.
	110	+ * However, only non-deleted Nodes need to be reachable from
	111	+ * dequeued Nodes, and reachability does not necessarily have to
	112	+ * be of the kind understood by the GC. We use the trick of
	113	+ * linking a Node that has just been dequeued to itself. Such a
	114	+ * self-link implicitly means to advance to head.next.
	115	+ */
	116	+
	117	+ /**
	118	+ * Linked list node class
	119	+ */
	120	+ static class Node<E> {
	121	+ E item;
	122	+
	123	+ /**
	124	+ * One of:
	125	+ * - the real successor Node
	126	+ * - this Node, meaning the successor is head.next
	127	+ * - null, meaning there is no successor (this is the last node)
	128	+ */
	129	+ Node<E> next;
	130	+
	131	+ Node(E x) { item = x; }
	132	+ }
	133	+
	134	+ /** The capacity bound, or Integer.MAX_VALUE if none */
	135	+ private final int capacity;
	136	+
	137	+ /** Current number of elements */
	138	+ private final AtomicInteger count = new AtomicInteger(0);
	139	+
	140	+ /**
	141	+ * Head of linked list.
	142	+ * Invariant: head.item == null
	143	+ */
	144	+ private transient Node<E> head;
	145	+
	146	+ /**
	147	+ * Tail of linked list.
	148	+ * Invariant: last.next == null
	149	+ */
	150	+ private transient Node<E> last;
	151	+
	152	+ /** Lock held by take, poll, etc */
	153	+ private final ReentrantLock takeLock = new ReentrantLock();
	154	+
	155	+ /** Wait queue for waiting takes */
	156	+ private final Condition notEmpty = takeLock.newCondition();
	157	+
	158	+ /** Lock held by put, offer, etc */
	159	+ private final ReentrantLock putLock = new ReentrantLock();
	160	+
	161	+ /** Wait queue for waiting puts */
	162	+ private final Condition notFull = putLock.newCondition();
	163	+
	164	+ /**
	165	+ * Signals a waiting take. Called only from put/offer (which do not
	166	+ * otherwise ordinarily lock takeLock.)
	167	+ */
	168	+ private void signalNotEmpty() {
	169	+ final ReentrantLock takeLock = this.takeLock;
	170	+ takeLock.lock();
	171	+ try {
	172	+ notEmpty.signal();
	173	+ } finally {
	174	+ takeLock.unlock();
	175	+ }
	176	+ }
	177	+
	178	+ /**
	179	+ * Signals a waiting put. Called only from take/poll.
	180	+ */
	181	+ private void signalNotFull() {
	182	+ final ReentrantLock putLock = this.putLock;
	183	+ putLock.lock();
	184	+ try {
	185	+ notFull.signal();
	186	+ } finally {
	187	+ putLock.unlock();
	188	+ }
	189	+ }
	190	+
	191	+ /**
	192	+ * Links node at end of queue.
	193	+ *
	194	+ * @param node the node
	195	+ */
	196	+ private void enqueue(Node<E> node) {
	197	+ // assert putLock.isHeldByCurrentThread();
	198	+ // assert last.next == null;
	199	+ last = last.next = node;
	200	+ }
	201	+
	202	+ /**
	203	+ * Removes a node from head of queue.
	204	+ *
	205	+ * @return the node
	206	+ */
	207	+ private E dequeue() {
	208	+ // assert takeLock.isHeldByCurrentThread();
	209	+ // assert head.item == null;
	210	+ Node<E> h = head;
	211	+ Node<E> first = h.next;
	212	+ h.next = h; // help GC
	213	+ head = first;
	214	+ E x = first.item;
	215	+ first.item = null;
	216	+ return x;
	217	+ }
	218	+
	219	+ /**
	220	+ * Lock to prevent both puts and takes.
	221	+ */
	222	+ void fullyLock() {
	223	+ putLock.lock();
	224	+ takeLock.lock();
	225	+ }
	226	+
	227	+ /**
	228	+ * Unlock to allow both puts and takes.
	229	+ */
	230	+ void fullyUnlock() {
	231	+ takeLock.unlock();
	232	+ putLock.unlock();
	233	+ }
	234	+
	235	+// /**
	236	+// * Tells whether both locks are held by current thread.
	237	+// */
	238	+// boolean isFullyLocked() {
	239	+// return (putLock.isHeldByCurrentThread() &&
	240	+// takeLock.isHeldByCurrentThread());
	241	+// }
	242	+
	243	+ /**
	244	+ * Creates a {@code LinkedBlockingQueue} with a capacity of
	245	+ * {@link Integer#MAX_VALUE}.
	246	+ */
	247	+ public LinkedBlockingQueue() {
	248	+ this(Integer.MAX_VALUE);
	249	+ }
	250	+
	251	+ /**
	252	+ * Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity.
	253	+ *
	254	+ * @param capacity the capacity of this queue
	255	+ * @throws IllegalArgumentException if {@code capacity} is not greater
	256	+ * than zero
	257	+ */
	258	+ public LinkedBlockingQueue(int capacity) {
	259	+ if (capacity <= 0) throw new IllegalArgumentException();
	260	+ this.capacity = capacity;
	261	+ last = head = new Node<E>(null);
	262	+ }
	263	+
	264	+ /**
	265	+ * Creates a {@code LinkedBlockingQueue} with a capacity of
	266	+ * {@link Integer#MAX_VALUE}, initially containing the elements of the
	267	+ * given collection,
	268	+ * added in traversal order of the collection's iterator.
	269	+ *
	270	+ * @param c the collection of elements to initially contain
	271	+ * @throws NullPointerException if the specified collection or any
	272	+ * of its elements are null
	273	+ */
	274	+ public LinkedBlockingQueue(Collection<? extends E> c) {
	275	+ this(Integer.MAX_VALUE);
	276	+ final ReentrantLock putLock = this.putLock;
	277	+ putLock.lock(); // Never contended, but necessary for visibility
	278	+ try {
	279	+ int n = 0;
	280	+ for (E e : c) {
	281	+ if (e == null)
	282	+ throw new NullPointerException();
	283	+ if (n == capacity)
	284	+ throw new IllegalStateException("Queue full");
	285	+ enqueue(new Node<E>(e));
	286	+ ++n;
	287	+ }
	288	+ count.set(n);
	289	+ } finally {
	290	+ putLock.unlock();
	291	+ }
	292	+ }
	293	+
	294	+
	295	+ // this doc comment is overridden to remove the reference to collections
	296	+ // greater in size than Integer.MAX_VALUE
	297	+ /**
	298	+ * Returns the number of elements in this queue.
	299	+ *
	300	+ * @return the number of elements in this queue
	301	+ */
	302	+ public int size() {
	303	+ return count.get();
	304	+ }
	305	+
	306	+ // this doc comment is a modified copy of the inherited doc comment,
	307	+ // without the reference to unlimited queues.
	308	+ /**
	309	+ * Returns the number of additional elements that this queue can ideally
	310	+ * (in the absence of memory or resource constraints) accept without
	311	+ * blocking. This is always equal to the initial capacity of this queue
	312	+ * less the current {@code size} of this queue.
	313	+ *
	314	+ * <p>Note that you <em>cannot</em> always tell if an attempt to insert
	315	+ * an element will succeed by inspecting {@code remainingCapacity}
	316	+ * because it may be the case that another thread is about to
	317	+ * insert or remove an element.
	318	+ */
	319	+ public int remainingCapacity() {
	320	+ return capacity - count.get();
	321	+ }
	322	+
	323	+ /**
	324	+ * Inserts the specified element at the tail of this queue, waiting if
	325	+ * necessary for space to become available.
	326	+ *
	327	+ * @throws InterruptedException {@inheritDoc}
	328	+ * @throws NullPointerException {@inheritDoc}
	329	+ */
	330	+ public void put(E e) throws InterruptedException {
	331	+ if (e == null) throw new NullPointerException();
	332	+ // Note: convention in all put/take/etc is to preset local var
	333	+ // holding count negative to indicate failure unless set.
	334	+ int c = -1;
	335	+ Node<E> node = new Node(e);
	336	+ final ReentrantLock putLock = this.putLock;
	337	+ final AtomicInteger count = this.count;
	338	+ putLock.lockInterruptibly();
	339	+ try {
	340	+ /*
	341	+ * Note that count is used in wait guard even though it is
	342	+ * not protected by lock. This works because count can
	343	+ * only decrease at this point (all other puts are shut
	344	+ * out by lock), and we (or some other waiting put) are
	345	+ * signalled if it ever changes from capacity. Similarly
	346	+ * for all other uses of count in other wait guards.
	347	+ */
	348	+ while (count.get() == capacity) {
	349	+ notFull.await();
	350	+ }
	351	+ enqueue(node);
	352	+ c = count.getAndIncrement();
	353	+ if (c + 1 < capacity)
	354	+ notFull.signal();
	355	+ } finally {
	356	+ putLock.unlock();
	357	+ }
	358	+ if (c == 0)
	359	+ signalNotEmpty();
	360	+ }
	361	+
	362	+ /**
	363	+ * Inserts the specified element at the tail of this queue, waiting if
	364	+ * necessary up to the specified wait time for space to become available.
	365	+ *
	366	+ * @return {@code true} if successful, or {@code false} if
	367	+ * the specified waiting time elapses before space is available.
	368	+ * @throws InterruptedException {@inheritDoc}
	369	+ * @throws NullPointerException {@inheritDoc}
	370	+ */
	371	+ public boolean offer(E e, long timeout, TimeUnit unit)
	372	+ throws InterruptedException {
	373	+
	374	+ if (e == null) throw new NullPointerException();
	375	+ long nanos = unit.toNanos(timeout);
	376	+ int c = -1;
	377	+ final ReentrantLock putLock = this.putLock;
	378	+ final AtomicInteger count = this.count;
	379	+ putLock.lockInterruptibly();
	380	+ try {
	381	+ while (count.get() == capacity) {
	382	+ if (nanos <= 0)
	383	+ return false;
	384	+ nanos = notFull.awaitNanos(nanos);
	385	+ }
	386	+ enqueue(new Node<E>(e));
	387	+ c = count.getAndIncrement();
	388	+ if (c + 1 < capacity)
	389	+ notFull.signal();
	390	+ } finally {
	391	+ putLock.unlock();
	392	+ }
	393	+ if (c == 0)
	394	+ signalNotEmpty();
	395	+ return true;
	396	+ }
	397	+
	398	+ /**
	399	+ * Inserts the specified element at the tail of this queue if it is
	400	+ * possible to do so immediately without exceeding the queue's capacity,
	401	+ * returning {@code true} upon success and {@code false} if this queue
	402	+ * is full.
	403	+ * When using a capacity-restricted queue, this method is generally
	404	+ * preferable to method {@link BlockingQueue#add add}, which can fail to
	405	+ * insert an element only by throwing an exception.
	406	+ *
	407	+ * @throws NullPointerException if the specified element is null
	408	+ */
	409	+ public boolean offer(E e) {
	410	+ if (e == null) throw new NullPointerException();
	411	+ final AtomicInteger count = this.count;
	412	+ if (count.get() == capacity)
	413	+ return false;
	414	+ int c = -1;
	415	+ Node<E> node = new Node(e);
	416	+ final ReentrantLock putLock = this.putLock;
	417	+ putLock.lock();
	418	+ try {
	419	+ if (count.get() < capacity) {
	420	+ enqueue(node);
	421	+ c = count.getAndIncrement();
	422	+ if (c + 1 < capacity)
	423	+ notFull.signal();
	424	+ }
	425	+ } finally {
	426	+ putLock.unlock();
	427	+ }
	428	+ if (c == 0)
	429	+ signalNotEmpty();
	430	+ return c >= 0;
	431	+ }
	432	+
	433	+
	434	+ public E take() throws InterruptedException {
	435	+ E x;
	436	+ int c = -1;
	437	+ final AtomicInteger count = this.count;
	438	+ final ReentrantLock takeLock = this.takeLock;
	439	+ takeLock.lockInterruptibly();
	440	+ try {
	441	+ while (count.get() == 0) {
	442	+ notEmpty.await();
	443	+ }
	444	+ x = dequeue();
	445	+ c = count.getAndDecrement();
	446	+ if (c > 1)
	447	+ notEmpty.signal();
	448	+ } finally {
	449	+ takeLock.unlock();
	450	+ }
	451	+ if (c == capacity)
	452	+ signalNotFull();
	453	+ return x;
	454	+ }
	455	+
	456	+ public E poll(long timeout, TimeUnit unit) throws InterruptedException {
	457	+ E x = null;
	458	+ int c = -1;
	459	+ long nanos = unit.toNanos(timeout);
	460	+ final AtomicInteger count = this.count;
	461	+ final ReentrantLock takeLock = this.takeLock;
	462	+ takeLock.lockInterruptibly();
	463	+ try {
	464	+ while (count.get() == 0) {
	465	+ if (nanos <= 0)
	466	+ return null;
	467	+ nanos = notEmpty.awaitNanos(nanos);
	468	+ }
	469	+ x = dequeue();
	470	+ c = count.getAndDecrement();
	471	+ if (c > 1)
	472	+ notEmpty.signal();
	473	+ } finally {
	474	+ takeLock.unlock();
	475	+ }
	476	+ if (c == capacity)
	477	+ signalNotFull();
	478	+ return x;
	479	+ }
	480	+
	481	+ public E poll() {
	482	+ final AtomicInteger count = this.count;
	483	+ if (count.get() == 0)
	484	+ return null;
	485	+ E x = null;
	486	+ int c = -1;
	487	+ final ReentrantLock takeLock = this.takeLock;
	488	+ takeLock.lock();
	489	+ try {
	490	+ if (count.get() > 0) {
	491	+ x = dequeue();
	492	+ c = count.getAndDecrement();
	493	+ if (c > 1)
	494	+ notEmpty.signal();
	495	+ }
	496	+ } finally {
	497	+ takeLock.unlock();
	498	+ }
	499	+ if (c == capacity)
	500	+ signalNotFull();
	501	+ return x;
	502	+ }
	503	+
	504	+ public E peek() {
	505	+ if (count.get() == 0)
	506	+ return null;
	507	+ final ReentrantLock takeLock = this.takeLock;
	508	+ takeLock.lock();
	509	+ try {
	510	+ Node<E> first = head.next;
	511	+ if (first == null)
	512	+ return null;
	513	+ else
	514	+ return first.item;
	515	+ } finally {
	516	+ takeLock.unlock();
	517	+ }
	518	+ }
	519	+
	520	+ /**
	521	+ * Unlinks interior Node p with predecessor trail.
	522	+ */
	523	+ void unlink(Node<E> p, Node<E> trail) {
	524	+ // assert isFullyLocked();
	525	+ // p.next is not changed, to allow iterators that are
	526	+ // traversing p to maintain their weak-consistency guarantee.
	527	+ p.item = null;
	528	+ trail.next = p.next;
	529	+ if (last == p)
	530	+ last = trail;
	531	+ if (count.getAndDecrement() == capacity)
	532	+ notFull.signal();
	533	+ }
	534	+
	535	+ /**
	536	+ * Removes a single instance of the specified element from this queue,
	537	+ * if it is present. More formally, removes an element {@code e} such
	538	+ * that {@code o.equals(e)}, if this queue contains one or more such
	539	+ * elements.
	540	+ * Returns {@code true} if this queue contained the specified element
	541	+ * (or equivalently, if this queue changed as a result of the call).
	542	+ *
	543	+ * @param o element to be removed from this queue, if present
	544	+ * @return {@code true} if this queue changed as a result of the call
	545	+ */
	546	+ public boolean remove(Object o) {
	547	+ if (o == null) return false;
	548	+ fullyLock();
	549	+ try {
	550	+ for (Node<E> trail = head, p = trail.next;
	551	+ p != null;
	552	+ trail = p, p = p.next) {
	553	+ if (o.equals(p.item)) {
	554	+ unlink(p, trail);
	555	+ return true;
	556	+ }
	557	+ }
	558	+ return false;
	559	+ } finally {
	560	+ fullyUnlock();
	561	+ }
	562	+ }
	563	+
	564	+ /**
	565	+ * Returns {@code true} if this queue contains the specified element.
	566	+ * More formally, returns {@code true} if and only if this queue contains
	567	+ * at least one element {@code e} such that {@code o.equals(e)}.
	568	+ *
	569	+ * @param o object to be checked for containment in this queue
	570	+ * @return {@code true} if this queue contains the specified element
	571	+ */
	572	+ public boolean contains(Object o) {
	573	+ if (o == null) return false;
	574	+ fullyLock();
	575	+ try {
	576	+ for (Node<E> p = head.next; p != null; p = p.next)
	577	+ if (o.equals(p.item))
	578	+ return true;
	579	+ return false;
	580	+ } finally {
	581	+ fullyUnlock();
	582	+ }
	583	+ }
	584	+
	585	+ /**
	586	+ * Returns an array containing all of the elements in this queue, in
	587	+ * proper sequence.
	588	+ *
	589	+ * <p>The returned array will be "safe" in that no references to it are
	590	+ * maintained by this queue. (In other words, this method must allocate
	591	+ * a new array). The caller is thus free to modify the returned array.
	592	+ *
	593	+ * <p>This method acts as bridge between array-based and collection-based
	594	+ * APIs.
	595	+ *
	596	+ * @return an array containing all of the elements in this queue
	597	+ */
	598	+ public Object[] toArray() {
	599	+ fullyLock();
	600	+ try {
	601	+ int size = count.get();
	602	+ Object[] a = new Object[size];
	603	+ int k = 0;
	604	+ for (Node<E> p = head.next; p != null; p = p.next)
	605	+ a[k++] = p.item;
	606	+ return a;
	607	+ } finally {
	608	+ fullyUnlock();
	609	+ }
	610	+ }
	611	+
	612	+ /**
	613	+ * Returns an array containing all of the elements in this queue, in
	614	+ * proper sequence; the runtime type of the returned array is that of
	615	+ * the specified array. If the queue fits in the specified array, it
	616	+ * is returned therein. Otherwise, a new array is allocated with the
	617	+ * runtime type of the specified array and the size of this queue.
	618	+ *
	619	+ * <p>If this queue fits in the specified array with room to spare
	620	+ * (i.e., the array has more elements than this queue), the element in
	621	+ * the array immediately following the end of the queue is set to
	622	+ * {@code null}.
	623	+ *
	624	+ * <p>Like the {@link #toArray()} method, this method acts as bridge between
	625	+ * array-based and collection-based APIs. Further, this method allows
	626	+ * precise control over the runtime type of the output array, and may,
	627	+ * under certain circumstances, be used to save allocation costs.
	628	+ *
	629	+ * <p>Suppose {@code x} is a queue known to contain only strings.
	630	+ * The following code can be used to dump the queue into a newly
	631	+ * allocated array of {@code String}:
	632	+ *
	633	+ * <pre>
	634	+ * String[] y = x.toArray(new String[0]);</pre>
	635	+ *
	636	+ * Note that {@code toArray(new Object[0])} is identical in function to
	637	+ * {@code toArray()}.
	638	+ *
	639	+ * @param a the array into which the elements of the queue are to
	640	+ * be stored, if it is big enough; otherwise, a new array of the
	641	+ * same runtime type is allocated for this purpose
	642	+ * @return an array containing all of the elements in this queue
	643	+ * @throws ArrayStoreException if the runtime type of the specified array
	644	+ * is not a supertype of the runtime type of every element in
	645	+ * this queue
	646	+ * @throws NullPointerException if the specified array is null
	647	+ */
	648	+ @SuppressWarnings("unchecked")
	649	+ public <T> T[] toArray(T[] a) {
	650	+ fullyLock();
	651	+ try {
	652	+ int size = count.get();
	653	+ if (a.length < size)
	654	+ a = (T[])java.lang.reflect.Array.newInstance
	655	+ (a.getClass().getComponentType(), size);
	656	+
	657	+ int k = 0;
	658	+ for (Node<E> p = head.next; p != null; p = p.next)
	659	+ a[k++] = (T)p.item;
	660	+ if (a.length > k)
	661	+ a[k] = null;
	662	+ return a;
	663	+ } finally {
	664	+ fullyUnlock();
	665	+ }
	666	+ }
	667	+
	668	+ public String toString() {
	669	+ fullyLock();
	670	+ try {
	671	+ Node<E> p = head.next;
	672	+ if (p == null)
	673	+ return "[]";
	674	+
	675	+ StringBuilder sb = new StringBuilder();
	676	+ sb.append('[');
	677	+ for (;;) {
	678	+ E e = p.item;
	679	+ sb.append(e == this ? "(this Collection)" : e);
	680	+ p = p.next;
	681	+ if (p == null)
	682	+ return sb.append(']').toString();
	683	+ sb.append(',').append(' ');
	684	+ }
	685	+ } finally {
	686	+ fullyUnlock();
	687	+ }
	688	+ }
	689	+
	690	+ /**
	691	+ * Atomically removes all of the elements from this queue.
	692	+ * The queue will be empty after this call returns.
	693	+ */
	694	+ public void clear() {
	695	+ fullyLock();
	696	+ try {
	697	+ for (Node<E> p, h = head; (p = h.next) != null; h = p) {
	698	+ h.next = h;
	699	+ p.item = null;
	700	+ }
	701	+ head = last;
	702	+ // assert head.item == null && head.next == null;
	703	+ if (count.getAndSet(0) == capacity)
	704	+ notFull.signal();
	705	+ } finally {
	706	+ fullyUnlock();
	707	+ }
	708	+ }
	709	+
	710	+ /**
	711	+ * @throws UnsupportedOperationException {@inheritDoc}
	712	+ * @throws ClassCastException {@inheritDoc}
	713	+ * @throws NullPointerException {@inheritDoc}
	714	+ * @throws IllegalArgumentException {@inheritDoc}
	715	+ */
	716	+ public int drainTo(Collection<? super E> c) {
	717	+ return drainTo(c, Integer.MAX_VALUE);
	718	+ }
	719	+
	720	+ /**
	721	+ * @throws UnsupportedOperationException {@inheritDoc}
	722	+ * @throws ClassCastException {@inheritDoc}
	723	+ * @throws NullPointerException {@inheritDoc}
	724	+ * @throws IllegalArgumentException {@inheritDoc}
	725	+ */
	726	+ public int drainTo(Collection<? super E> c, int maxElements) {
	727	+ if (c == null)
	728	+ throw new NullPointerException();
	729	+ if (c == this)
	730	+ throw new IllegalArgumentException();
	731	+ boolean signalNotFull = false;
	732	+ final ReentrantLock takeLock = this.takeLock;
	733	+ takeLock.lock();
	734	+ try {
	735	+ int n = Math.min(maxElements, count.get());
	736	+ // count.get provides visibility to first n Nodes
	737	+ Node<E> h = head;
	738	+ int i = 0;
	739	+ try {
	740	+ while (i < n) {
	741	+ Node<E> p = h.next;
	742	+ c.add(p.item);
	743	+ p.item = null;
	744	+ h.next = h;
	745	+ h = p;
	746	+ ++i;
	747	+ }
	748	+ return n;
	749	+ } finally {
	750	+ // Restore invariants even if c.add() threw
	751	+ if (i > 0) {
	752	+ // assert h.item == null;
	753	+ head = h;
	754	+ signalNotFull = (count.getAndAdd(-i) == capacity);
	755	+ }
	756	+ }
	757	+ } finally {
	758	+ takeLock.unlock();
	759	+ if (signalNotFull)
	760	+ signalNotFull();
	761	+ }
	762	+ }
	763	+
	764	+ /**
	765	+ * Returns an iterator over the elements in this queue in proper sequence.
	766	+ * The elements will be returned in order from first (head) to last (tail).
	767	+ *
	768	+ * <p>The returned iterator is a "weakly consistent" iterator that
	769	+ * will never throw {@link java.util.ConcurrentModificationException
	770	+ * ConcurrentModificationException}, and guarantees to traverse
	771	+ * elements as they existed upon construction of the iterator, and
	772	+ * may (but is not guaranteed to) reflect any modifications
	773	+ * subsequent to construction.
	774	+ *
	775	+ * @return an iterator over the elements in this queue in proper sequence
	776	+ */
	777	+ public Iterator<E> iterator() {
	778	+ return new Itr();
	779	+ }
	780	+
	781	+ private class Itr implements Iterator<E> {
	782	+ /*
	783	+ * Basic weakly-consistent iterator. At all times hold the next
	784	+ * item to hand out so that if hasNext() reports true, we will
	785	+ * still have it to return even if lost race with a take etc.
	786	+ */
	787	+ private Node<E> current;
	788	+ private Node<E> lastRet;
	789	+ private E currentElement;
	790	+
	791	+ Itr() {
	792	+ fullyLock();
	793	+ try {
	794	+ current = head.next;
	795	+ if (current != null)
	796	+ currentElement = current.item;
	797	+ } finally {
	798	+ fullyUnlock();
	799	+ }
	800	+ }
	801	+
	802	+ public boolean hasNext() {
	803	+ return current != null;
	804	+ }
	805	+
	806	+ /**
	807	+ * Returns the next live successor of p, or null if no such.
	808	+ *
	809	+ * Unlike other traversal methods, iterators need to handle both:
	810	+ * - dequeued nodes (p.next == p)
	811	+ * - (possibly multiple) interior removed nodes (p.item == null)
	812	+ */
	813	+ private Node<E> nextNode(Node<E> p) {
	814	+ for (;;) {
	815	+ Node<E> s = p.next;
	816	+ if (s == p)
	817	+ return head.next;
	818	+ if (s == null \|\| s.item != null)
	819	+ return s;
	820	+ p = s;
	821	+ }
	822	+ }
	823	+
	824	+ public E next() {
	825	+ fullyLock();
	826	+ try {
	827	+ if (current == null)
	828	+ throw new NoSuchElementException();
	829	+ E x = currentElement;
	830	+ lastRet = current;
	831	+ current = nextNode(current);
	832	+ currentElement = (current == null) ? null : current.item;
	833	+ return x;
	834	+ } finally {
	835	+ fullyUnlock();
	836	+ }
	837	+ }
	838	+
	839	+ public void remove() {
	840	+ if (lastRet == null)
	841	+ throw new IllegalStateException();
	842	+ fullyLock();
	843	+ try {
	844	+ Node<E> node = lastRet;
	845	+ lastRet = null;
	846	+ for (Node<E> trail = head, p = trail.next;
	847	+ p != null;
	848	+ trail = p, p = p.next) {
	849	+ if (p == node) {
	850	+ unlink(p, trail);
	851	+ break;
	852	+ }
	853	+ }
	854	+ } finally {
	855	+ fullyUnlock();
	856	+ }
	857	+ }
	858	+ }
	859	+
	860	+ /**
	861	+ * Save the state to a stream (that is, serialize it).
	862	+ *
	863	+ * @serialData The capacity is emitted (int), followed by all of
	864	+ * its elements (each an {@code Object}) in the proper order,
	865	+ * followed by a null
	866	+ * @param s the stream
	867	+ */
	868	+ private void writeObject(java.io.ObjectOutputStream s)
	869	+ throws java.io.IOException {
	870	+
	871	+ fullyLock();
	872	+ try {
	873	+ // Write out any hidden stuff, plus capacity
	874	+ s.defaultWriteObject();
	875	+
	876	+ // Write out all elements in the proper order.
	877	+ for (Node<E> p = head.next; p != null; p = p.next)
	878	+ s.writeObject(p.item);
	879	+
	880	+ // Use trailing null as sentinel
	881	+ s.writeObject(null);
	882	+ } finally {
	883	+ fullyUnlock();
	884	+ }
	885	+ }
	886	+
	887	+ /**
	888	+ * Reconstitute this queue instance from a stream (that is,
	889	+ * deserialize it).
	890	+ *
	891	+ * @param s the stream
	892	+ */
	893	+ private void readObject(java.io.ObjectInputStream s)
	894	+ throws java.io.IOException, ClassNotFoundException {
	895	+ // Read in capacity, and any hidden stuff
	896	+ s.defaultReadObject();
	897	+
	898	+ count.set(0);
	899	+ last = head = new Node<E>(null);
	900	+
	901	+ // Read in all elements and place in queue
	902	+ for (;;) {
	903	+ @SuppressWarnings("unchecked")
	904	+ E item = (E)s.readObject();
	905	+ if (item == null)
	906	+ break;
	907	+ add(item);
	908	+ }
	909	+ }
	910	+}