Java tutorial
/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /* * This file is available under and governed by the GNU General Public * License version 2 only, as published by the Free Software Foundation. * However, the following notice accompanied the original version of this * file: * * 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/publicdomain/zero/1.0/ */ package java.util.concurrent; import java.util.AbstractQueue; import java.util.Collection; import java.util.Iterator; import java.util.NoSuchElementException; import java.util.Objects; import java.util.Spliterator; import java.util.Spliterators; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; import java.util.function.Consumer; import java.util.function.Predicate; /** * An optionally-bounded {@linkplain BlockingQueue blocking 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. * Linked queues typically have higher throughput than array-based queues but * less predictable performance in most concurrent applications. * * <p>The optional capacity bound constructor argument serves as a * way to prevent excessive queue expansion. The capacity, if unspecified, * is equal to {@link Integer#MAX_VALUE}. Linked nodes are * dynamically created upon each insertion unless this would bring the * queue above capacity. * * <p>This class and its iterator implement all of the <em>optional</em> * methods of the {@link Collection} and {@link Iterator} interfaces. * * <p>This class is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @since 1.5 * @author Doug Lea * @param <E> the type of elements held in this queue */ public class LinkedBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, java.io.Serializable { private static final long serialVersionUID = -6903933977591709194L; /* * A variant of the "two lock queue" algorithm. The putLock gates * entry to put (and offer), and has an associated condition for * waiting puts. Similarly for the takeLock. The "count" field * that they both rely on is maintained as an atomic to avoid * needing to get both locks in most cases. Also, to minimize need * for puts to get takeLock and vice-versa, cascading notifies are * used. When a put notices that it has enabled at least one take, * it signals taker. That taker in turn signals others if more * items have been entered since the signal. And symmetrically for * takes signalling puts. Operations such as remove(Object) and * iterators acquire both locks. * * Visibility between writers and readers is provided as follows: * * Whenever an element is enqueued, the putLock is acquired and * count updated. A subsequent reader guarantees visibility to the * enqueued Node by either acquiring the putLock (via fullyLock) * or by acquiring the takeLock, and then reading n = count.get(); * this gives visibility to the first n items. * * To implement weakly consistent iterators, it appears we need to * keep all Nodes GC-reachable from a predecessor dequeued Node. * That would cause two problems: * - allow a rogue Iterator to cause unbounded memory retention * - cause cross-generational linking of old Nodes to new Nodes if * a Node was tenured while live, which generational GCs have a * hard time dealing with, causing repeated major collections. * However, only non-deleted Nodes need to be reachable from * dequeued Nodes, and reachability does not necessarily have to * be of the kind understood by the GC. We use the trick of * linking a Node that has just been dequeued to itself. Such a * self-link implicitly means to advance to head.next. */ /** * Linked list node class. */ static class Node<E> { E item; /** * One of: * - the real successor Node * - this Node, meaning the successor is head.next * - null, meaning there is no successor (this is the last node) */ Node<E> next; Node(E x) { item = x; } } /** The capacity bound, or Integer.MAX_VALUE if none */ private final int capacity; /** Current number of elements */ private final AtomicInteger count = new AtomicInteger(); /** * Head of linked list. * Invariant: head.item == null */ transient Node<E> head; /** * Tail of linked list. * Invariant: last.next == null */ private transient Node<E> last; /** Lock held by take, poll, etc */ private final ReentrantLock takeLock = new ReentrantLock(); /** Wait queue for waiting takes */ private final Condition notEmpty = takeLock.newCondition(); /** Lock held by put, offer, etc */ private final ReentrantLock putLock = new ReentrantLock(); /** Wait queue for waiting puts */ private final Condition notFull = putLock.newCondition(); /** * Signals a waiting take. Called only from put/offer (which do not * otherwise ordinarily lock takeLock.) */ private void signalNotEmpty() { final ReentrantLock takeLock = this.takeLock; takeLock.lock(); try { notEmpty.signal(); } finally { takeLock.unlock(); } } /** * Signals a waiting put. Called only from take/poll. */ private void signalNotFull() { final ReentrantLock putLock = this.putLock; putLock.lock(); try { notFull.signal(); } finally { putLock.unlock(); } } /** * Links node at end of queue. * * @param node the node */ private void enqueue(Node<E> node) { // assert putLock.isHeldByCurrentThread(); // assert last.next == null; last = last.next = node; } /** * Removes a node from head of queue. * * @return the node */ private E dequeue() { // assert takeLock.isHeldByCurrentThread(); // assert head.item == null; Node<E> h = head; Node<E> first = h.next; h.next = h; // help GC head = first; E x = first.item; first.item = null; return x; } /** * Locks to prevent both puts and takes. */ void fullyLock() { putLock.lock(); takeLock.lock(); } /** * Unlocks to allow both puts and takes. */ void fullyUnlock() { takeLock.unlock(); putLock.unlock(); } /** * Creates a {@code LinkedBlockingQueue} with a capacity of * {@link Integer#MAX_VALUE}. */ public LinkedBlockingQueue() { this(Integer.MAX_VALUE); } /** * Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. * * @param capacity the capacity of this queue * @throws IllegalArgumentException if {@code capacity} is not greater * than zero */ public LinkedBlockingQueue(int capacity) { if (capacity <= 0) throw new IllegalArgumentException(); this.capacity = capacity; last = head = new Node<E>(null); } /** * Creates a {@code LinkedBlockingQueue} with a capacity of * {@link Integer#MAX_VALUE}, 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 LinkedBlockingQueue(Collection<? extends E> c) { this(Integer.MAX_VALUE); final ReentrantLock putLock = this.putLock; putLock.lock(); // Never contended, but necessary for visibility try { int n = 0; for (E e : c) { if (e == null) throw new NullPointerException(); if (n == capacity) throw new IllegalStateException("Queue full"); enqueue(new Node<E>(e)); ++n; } count.set(n); } finally { putLock.unlock(); } } // this doc comment is overridden to remove the reference to collections // greater in size than Integer.MAX_VALUE /** * Returns the number of elements in this queue. * * @return the number of elements in this queue */ public int size() { return count.get(); } // this doc comment is a modified copy of the inherited doc comment, // without the reference to unlimited queues. /** * Returns the number of additional elements that this queue can ideally * (in the absence of memory or resource constraints) accept without * blocking. This is always equal to the initial capacity of this queue * less the current {@code size} of this queue. * * <p>Note that you <em>cannot</em> always tell if an attempt to insert * an element will succeed by inspecting {@code remainingCapacity} * because it may be the case that another thread is about to * insert or remove an element. */ public int remainingCapacity() { return capacity - count.get(); } /** * Inserts the specified element at the tail of this queue, waiting if * necessary for space to become available. * * @throws InterruptedException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public void put(E e) throws InterruptedException { if (e == null) throw new NullPointerException(); final int c; final Node<E> node = new Node<E>(e); final ReentrantLock putLock = this.putLock; final AtomicInteger count = this.count; putLock.lockInterruptibly(); try { /* * Note that count is used in wait guard even though it is * not protected by lock. This works because count can * only decrease at this point (all other puts are shut * out by lock), and we (or some other waiting put) are * signalled if it ever changes from capacity. Similarly * for all other uses of count in other wait guards. */ while (count.get() == capacity) { notFull.await(); } enqueue(node); c = count.getAndIncrement(); if (c + 1 < capacity) notFull.signal(); } finally { putLock.unlock(); } if (c == 0) signalNotEmpty(); } /** * Inserts the specified element at the tail of this queue, waiting if * necessary up to the specified wait time for space to become available. * * @return {@code true} if successful, or {@code false} if * the specified waiting time elapses before space is available * @throws InterruptedException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException { if (e == null) throw new NullPointerException(); long nanos = unit.toNanos(timeout); final int c; final ReentrantLock putLock = this.putLock; final AtomicInteger count = this.count; putLock.lockInterruptibly(); try { while (count.get() == capacity) { if (nanos <= 0L) return false; nanos = notFull.awaitNanos(nanos); } enqueue(new Node<E>(e)); c = count.getAndIncrement(); if (c + 1 < capacity) notFull.signal(); } finally { putLock.unlock(); } if (c == 0) signalNotEmpty(); return true; } /** * Inserts the specified element at the tail of this queue if it is * possible to do so immediately without exceeding the queue's capacity, * returning {@code true} upon success and {@code false} if this queue * is full. * When using a capacity-restricted queue, this method is generally * preferable to method {@link BlockingQueue#add add}, which can fail to * insert an element only by throwing an exception. * * @throws NullPointerException if the specified element is null */ public boolean offer(E e) { if (e == null) throw new NullPointerException(); final AtomicInteger count = this.count; if (count.get() == capacity) return false; final int c; final Node<E> node = new Node<E>(e); final ReentrantLock putLock = this.putLock; putLock.lock(); try { if (count.get() == capacity) return false; enqueue(node); c = count.getAndIncrement(); if (c + 1 < capacity) notFull.signal(); } finally { putLock.unlock(); } if (c == 0) signalNotEmpty(); return true; } public E take() throws InterruptedException { final E x; final int c; final AtomicInteger count = this.count; final ReentrantLock takeLock = this.takeLock; takeLock.lockInterruptibly(); try { while (count.get() == 0) { notEmpty.await(); } x = dequeue(); c = count.getAndDecrement(); if (c > 1) notEmpty.signal(); } finally { takeLock.unlock(); } if (c == capacity) signalNotFull(); return x; } public E poll(long timeout, TimeUnit unit) throws InterruptedException { final E x; final int c; long nanos = unit.toNanos(timeout); final AtomicInteger count = this.count; final ReentrantLock takeLock = this.takeLock; takeLock.lockInterruptibly(); try { while (count.get() == 0) { if (nanos <= 0L) return null; nanos = notEmpty.awaitNanos(nanos); } x = dequeue(); c = count.getAndDecrement(); if (c > 1) notEmpty.signal(); } finally { takeLock.unlock(); } if (c == capacity) signalNotFull(); return x; } public E poll() { final AtomicInteger count = this.count; if (count.get() == 0) return null; final E x; final int c; final ReentrantLock takeLock = this.takeLock; takeLock.lock(); try { if (count.get() == 0) return null; x = dequeue(); c = count.getAndDecrement(); if (c > 1) notEmpty.signal(); } finally { takeLock.unlock(); } if (c == capacity) signalNotFull(); return x; } public E peek() { final AtomicInteger count = this.count; if (count.get() == 0) return null; final ReentrantLock takeLock = this.takeLock; takeLock.lock(); try { return (count.get() > 0) ? head.next.item : null; } finally { takeLock.unlock(); } } /** * Unlinks interior Node p with predecessor pred. */ void unlink(Node<E> p, Node<E> pred) { // assert putLock.isHeldByCurrentThread(); // assert takeLock.isHeldByCurrentThread(); // p.next is not changed, to allow iterators that are // traversing p to maintain their weak-consistency guarantee. p.item = null; pred.next = p.next; if (last == p) last = pred; if (count.getAndDecrement() == capacity) notFull.signal(); } /** * Removes a single instance of the specified element from this queue, * if it is present. More formally, removes an element {@code e} such * that {@code o.equals(e)}, if this queue contains one or more such * elements. * Returns {@code true} 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 {@code true} if this queue changed as a result of the call */ public boolean remove(Object o) { if (o == null) return false; fullyLock(); try { for (Node<E> pred = head, p = pred.next; p != null; pred = p, p = p.next) { if (o.equals(p.item)) { unlink(p, pred); return true; } } return false; } finally { fullyUnlock(); } } /** * Returns {@code true} if this queue contains the specified element. * More formally, returns {@code true} if and only if this queue contains * at least one element {@code e} such that {@code o.equals(e)}. * * @param o object to be checked for containment in this queue * @return {@code true} if this queue contains the specified element */ public boolean contains(Object o) { if (o == null) return false; fullyLock(); try { for (Node<E> p = head.next; p != null; p = p.next) if (o.equals(p.item)) return true; return false; } finally { fullyUnlock(); } } /** * Returns an array containing all of the elements in this queue, in * proper sequence. * * <p>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. * * <p>This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all of the elements in this queue */ public Object[] toArray() { fullyLock(); try { int size = count.get(); Object[] a = new Object[size]; int k = 0; for (Node<E> p = head.next; p != null; p = p.next) a[k++] = p.item; return a; } finally { fullyUnlock(); } } /** * 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. * * <p>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 * {@code null}. * * <p>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. * * <p>Suppose {@code 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 {@code String}: * * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> * * Note that {@code toArray(new Object[0])} is identical in function to * {@code toArray()}. * * @param a the array into which the elements of the queue are to * be stored, if it is big enough; otherwise, a new array of the * same runtime type is allocated for this purpose * @return an array containing all of the elements in this queue * @throws ArrayStoreException if the runtime type of the specified array * is not a supertype of the runtime type of every element in * this queue * @throws NullPointerException if the specified array is null */ @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { fullyLock(); try { int size = count.get(); if (a.length < size) a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size); int k = 0; for (Node<E> p = head.next; p != null; p = p.next) a[k++] = (T) p.item; if (a.length > k) a[k] = null; return a; } finally { fullyUnlock(); } } public String toString() { return Helpers.collectionToString(this); } /** * Atomically removes all of the elements from this queue. * The queue will be empty after this call returns. */ public void clear() { fullyLock(); try { for (Node<E> p, h = head; (p = h.next) != null; h = p) { h.next = h; p.item = null; } head = last; // assert head.item == null && head.next == null; if (count.getAndSet(0) == capacity) notFull.signal(); } finally { fullyUnlock(); } } /** * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} */ public int drainTo(Collection<? super E> c) { return drainTo(c, Integer.MAX_VALUE); } /** * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} */ public int drainTo(Collection<? super E> c, int maxElements) { Objects.requireNonNull(c); if (c == this) throw new IllegalArgumentException(); if (maxElements <= 0) return 0; boolean signalNotFull = false; final ReentrantLock takeLock = this.takeLock; takeLock.lock(); try { int n = Math.min(maxElements, count.get()); // count.get provides visibility to first n Nodes Node<E> h = head; int i = 0; try { while (i < n) { Node<E> p = h.next; c.add(p.item); p.item = null; h.next = h; h = p; ++i; } return n; } finally { // Restore invariants even if c.add() threw if (i > 0) { // assert h.item == null; head = h; signalNotFull = (count.getAndAdd(-i) == capacity); } } } finally { takeLock.unlock(); if (signalNotFull) signalNotFull(); } } /** * Used for any element traversal that is not entirely under lock. * Such traversals must handle both: * - dequeued nodes (p.next == p) * - (possibly multiple) interior removed nodes (p.item == null) */ Node<E> succ(Node<E> p) { if (p == (p = p.next)) p = head.next; return p; } /** * Returns an iterator over the elements in this queue in proper sequence. * The elements will be returned in order from first (head) to last (tail). * * <p>The returned iterator is * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. * * @return an iterator over the elements in this queue in proper sequence */ public Iterator<E> iterator() { return new Itr(); } /** * Weakly-consistent iterator. * * Lazily updated ancestor field provides expected O(1) remove(), * but still O(n) in the worst case, whenever the saved ancestor * is concurrently deleted. */ private class Itr implements Iterator<E> { private Node<E> next; // Node holding nextItem private E nextItem; // next item to hand out private Node<E> lastRet; private Node<E> ancestor; // Helps unlink lastRet on remove() Itr() { fullyLock(); try { if ((next = head.next) != null) nextItem = next.item; } finally { fullyUnlock(); } } public boolean hasNext() { return next != null; } public E next() { Node<E> p; if ((p = next) == null) throw new NoSuchElementException(); lastRet = p; E x = nextItem; fullyLock(); try { E e = null; for (p = p.next; p != null && (e = p.item) == null;) p = succ(p); next = p; nextItem = e; } finally { fullyUnlock(); } return x; } public void forEachRemaining(Consumer<? super E> action) { // A variant of forEachFrom Objects.requireNonNull(action); Node<E> p; if ((p = next) == null) return; lastRet = p; next = null; final int batchSize = 64; Object[] es = null; int n, len = 1; do { fullyLock(); try { if (es == null) { p = p.next; for (Node<E> q = p; q != null; q = succ(q)) if (q.item != null && ++len == batchSize) break; es = new Object[len]; es[0] = nextItem; nextItem = null; n = 1; } else n = 0; for (; p != null && n < len; p = succ(p)) if ((es[n] = p.item) != null) { lastRet = p; n++; } } finally { fullyUnlock(); } for (int i = 0; i < n; i++) { @SuppressWarnings("unchecked") E e = (E) es[i]; action.accept(e); } } while (n > 0 && p != null); } public void remove() { Node<E> p = lastRet; if (p == null) throw new IllegalStateException(); lastRet = null; fullyLock(); try { if (p.item != null) { if (ancestor == null) ancestor = head; ancestor = findPred(p, ancestor); unlink(p, ancestor); } } finally { fullyUnlock(); } } } /** * A customized variant of Spliterators.IteratorSpliterator. * Keep this class in sync with (very similar) LBDSpliterator. */ private final class LBQSpliterator implements Spliterator<E> { static final int MAX_BATCH = 1 << 25; // max batch array size; Node<E> current; // current node; null until initialized int batch; // batch size for splits boolean exhausted; // true when no more nodes long est = size(); // size estimate LBQSpliterator() { } public long estimateSize() { return est; } public Spliterator<E> trySplit() { Node<E> h; if (!exhausted && ((h = current) != null || (h = head.next) != null) && h.next != null) { int n = batch = Math.min(batch + 1, MAX_BATCH); Object[] a = new Object[n]; int i = 0; Node<E> p = current; fullyLock(); try { if (p != null || (p = head.next) != null) for (; p != null && i < n; p = succ(p)) if ((a[i] = p.item) != null) i++; } finally { fullyUnlock(); } if ((current = p) == null) { est = 0L; exhausted = true; } else if ((est -= i) < 0L) est = 0L; if (i > 0) return Spliterators.spliterator(a, 0, i, (Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.CONCURRENT)); } return null; } public boolean tryAdvance(Consumer<? super E> action) { Objects.requireNonNull(action); if (!exhausted) { E e = null; fullyLock(); try { Node<E> p; if ((p = current) != null || (p = head.next) != null) do { e = p.item; p = succ(p); } while (e == null && p != null); if ((current = p) == null) exhausted = true; } finally { fullyUnlock(); } if (e != null) { action.accept(e); return true; } } return false; } public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); if (!exhausted) { exhausted = true; Node<E> p = current; current = null; forEachFrom(action, p); } } public int characteristics() { return (Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.CONCURRENT); } } /** * Returns a {@link Spliterator} over the elements in this queue. * * <p>The returned spliterator is * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. * * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. * * @implNote * The {@code Spliterator} implements {@code trySplit} to permit limited * parallelism. * * @return a {@code Spliterator} over the elements in this queue * @since 1.8 */ public Spliterator<E> spliterator() { return new LBQSpliterator(); } /** * @throws NullPointerException {@inheritDoc} */ public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); forEachFrom(action, null); } /** * Runs action on each element found during a traversal starting at p. * If p is null, traversal starts at head. */ void forEachFrom(Consumer<? super E> action, Node<E> p) { // Extract batches of elements while holding the lock; then // run the action on the elements while not final int batchSize = 64; // max number of elements per batch Object[] es = null; // container for batch of elements int n, len = 0; do { fullyLock(); try { if (es == null) { if (p == null) p = head.next; for (Node<E> q = p; q != null; q = succ(q)) if (q.item != null && ++len == batchSize) break; es = new Object[len]; } for (n = 0; p != null && n < len; p = succ(p)) if ((es[n] = p.item) != null) n++; } finally { fullyUnlock(); } for (int i = 0; i < n; i++) { @SuppressWarnings("unchecked") E e = (E) es[i]; action.accept(e); } } while (n > 0 && p != null); } /** * @throws NullPointerException {@inheritDoc} */ public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); return bulkRemove(filter); } /** * @throws NullPointerException {@inheritDoc} */ public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> c.contains(e)); } /** * @throws NullPointerException {@inheritDoc} */ public boolean retainAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> !c.contains(e)); } /** * Returns the predecessor of live node p, given a node that was * once a live ancestor of p (or head); allows unlinking of p. */ Node<E> findPred(Node<E> p, Node<E> ancestor) { // assert p.item != null; if (ancestor.item == null) ancestor = head; // Fails with NPE if precondition not satisfied for (Node<E> q; (q = ancestor.next) != p;) ancestor = q; return ancestor; } /** Implementation of bulk remove methods. */ @SuppressWarnings("unchecked") private boolean bulkRemove(Predicate<? super E> filter) { boolean removed = false; Node<E> p = null, ancestor = head; Node<E>[] nodes = null; int n, len = 0; do { // 1. Extract batch of up to 64 elements while holding the lock. fullyLock(); try { if (nodes == null) { // first batch; initialize p = head.next; for (Node<E> q = p; q != null; q = succ(q)) if (q.item != null && ++len == 64) break; nodes = (Node<E>[]) new Node<?>[len]; } for (n = 0; p != null && n < len; p = succ(p)) nodes[n++] = p; } finally { fullyUnlock(); } // 2. Run the filter on the elements while lock is free. long deathRow = 0L; // "bitset" of size 64 for (int i = 0; i < n; i++) { final E e; if ((e = nodes[i].item) != null && filter.test(e)) deathRow |= 1L << i; } // 3. Remove any filtered elements while holding the lock. if (deathRow != 0) { fullyLock(); try { for (int i = 0; i < n; i++) { final Node<E> q; if ((deathRow & (1L << i)) != 0L && (q = nodes[i]).item != null) { ancestor = findPred(q, ancestor); unlink(q, ancestor); removed = true; } nodes[i] = null; // help GC } } finally { fullyUnlock(); } } } while (n > 0 && p != null); return removed; } /** * Saves this queue to a stream (that is, serializes it). * * @param s the stream * @throws java.io.IOException if an I/O error occurs * @serialData The capacity is emitted (int), followed by all of * its elements (each an {@code Object}) in the proper order, * followed by a null */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { fullyLock(); try { // Write out any hidden stuff, plus capacity s.defaultWriteObject(); // Write out all elements in the proper order. for (Node<E> p = head.next; p != null; p = p.next) s.writeObject(p.item); // Use trailing null as sentinel s.writeObject(null); } finally { fullyUnlock(); } } /** * Reconstitutes this queue from a stream (that is, deserializes it). * @param s the stream * @throws ClassNotFoundException if the class of a serialized object * could not be found * @throws java.io.IOException if an I/O error occurs */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in capacity, and any hidden stuff s.defaultReadObject(); count.set(0); last = head = new Node<E>(null); // Read in all elements and place in queue for (;;) { @SuppressWarnings("unchecked") E item = (E) s.readObject(); if (item == null) break; add(item); } } }