jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent;
jaroslav@1890: 
jaroslav@1890: import java.util.concurrent.locks.*;
jaroslav@1890: import java.util.*;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * An unbounded {@linkplain BlockingQueue blocking queue} that uses
jaroslav@1890:  * the same ordering rules as class {@link PriorityQueue} and supplies
jaroslav@1890:  * blocking retrieval operations.  While this queue is logically
jaroslav@1890:  * unbounded, attempted additions may fail due to resource exhaustion
jaroslav@1890:  * (causing {@code OutOfMemoryError}). This class does not permit
jaroslav@1890:  * {@code null} elements.  A priority queue relying on {@linkplain
jaroslav@1890:  * Comparable natural ordering} also does not permit insertion of
jaroslav@1890:  * non-comparable objects (doing so results in
jaroslav@1890:  * {@code ClassCastException}).
jaroslav@1890:  *
jaroslav@1890:  * <p>This class and its iterator implement all of the
jaroslav@1890:  * <em>optional</em> methods of the {@link Collection} and {@link
jaroslav@1890:  * Iterator} interfaces.  The Iterator provided in method {@link
jaroslav@1890:  * #iterator()} is <em>not</em> guaranteed to traverse the elements of
jaroslav@1890:  * the PriorityBlockingQueue in any particular order. If you need
jaroslav@1890:  * ordered traversal, consider using
jaroslav@1890:  * {@code Arrays.sort(pq.toArray())}.  Also, method {@code drainTo}
jaroslav@1890:  * can be used to <em>remove</em> some or all elements in priority
jaroslav@1890:  * order and place them in another collection.
jaroslav@1890:  *
jaroslav@1890:  * <p>Operations on this class make no guarantees about the ordering
jaroslav@1890:  * of elements with equal priority. If you need to enforce an
jaroslav@1890:  * ordering, you can define custom classes or comparators that use a
jaroslav@1890:  * secondary key to break ties in primary priority values.  For
jaroslav@1890:  * example, here is a class that applies first-in-first-out
jaroslav@1890:  * tie-breaking to comparable elements. To use it, you would insert a
jaroslav@1890:  * {@code new FIFOEntry(anEntry)} instead of a plain entry object.
jaroslav@1890:  *
jaroslav@1890:  *  <pre> {@code
jaroslav@1890:  * class FIFOEntry<E extends Comparable<? super E>>
jaroslav@1890:  *     implements Comparable<FIFOEntry<E>> {
jaroslav@1890:  *   static final AtomicLong seq = new AtomicLong(0);
jaroslav@1890:  *   final long seqNum;
jaroslav@1890:  *   final E entry;
jaroslav@1890:  *   public FIFOEntry(E entry) {
jaroslav@1890:  *     seqNum = seq.getAndIncrement();
jaroslav@1890:  *     this.entry = entry;
jaroslav@1890:  *   }
jaroslav@1890:  *   public E getEntry() { return entry; }
jaroslav@1890:  *   public int compareTo(FIFOEntry<E> other) {
jaroslav@1890:  *     int res = entry.compareTo(other.entry);
jaroslav@1890:  *     if (res == 0 && other.entry != this.entry)
jaroslav@1890:  *       res = (seqNum < other.seqNum ? -1 : 1);
jaroslav@1890:  *     return res;
jaroslav@1890:  *   }
jaroslav@1890:  * }}</pre>
jaroslav@1890:  *
jaroslav@1890:  * <p>This class is a member of the
jaroslav@1890:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@1890:  * Java Collections Framework</a>.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.5
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  * @param <E> the type of elements held in this collection
jaroslav@1890:  */
jaroslav@1890: public class PriorityBlockingQueue<E> extends AbstractQueue<E>
jaroslav@1890:     implements BlockingQueue<E>, java.io.Serializable {
jaroslav@1890:     private static final long serialVersionUID = 5595510919245408276L;
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * The implementation uses an array-based binary heap, with public
jaroslav@1890:      * operations protected with a single lock. However, allocation
jaroslav@1890:      * during resizing uses a simple spinlock (used only while not
jaroslav@1890:      * holding main lock) in order to allow takes to operate
jaroslav@1890:      * concurrently with allocation.  This avoids repeated
jaroslav@1890:      * postponement of waiting consumers and consequent element
jaroslav@1890:      * build-up. The need to back away from lock during allocation
jaroslav@1890:      * makes it impossible to simply wrap delegated
jaroslav@1890:      * java.util.PriorityQueue operations within a lock, as was done
jaroslav@1890:      * in a previous version of this class. To maintain
jaroslav@1890:      * interoperability, a plain PriorityQueue is still used during
jaroslav@1890:      * serialization, which maintains compatibility at the espense of
jaroslav@1890:      * transiently doubling overhead.
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Default array capacity.
jaroslav@1890:      */
jaroslav@1890:     private static final int DEFAULT_INITIAL_CAPACITY = 11;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The maximum size of array to allocate.
jaroslav@1890:      * Some VMs reserve some header words in an array.
jaroslav@1890:      * Attempts to allocate larger arrays may result in
jaroslav@1890:      * OutOfMemoryError: Requested array size exceeds VM limit
jaroslav@1890:      */
jaroslav@1890:     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Priority queue represented as a balanced binary heap: the two
jaroslav@1890:      * children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
jaroslav@1890:      * priority queue is ordered by comparator, or by the elements'
jaroslav@1890:      * natural ordering, if comparator is null: For each node n in the
jaroslav@1890:      * heap and each descendant d of n, n <= d.  The element with the
jaroslav@1890:      * lowest value is in queue[0], assuming the queue is nonempty.
jaroslav@1890:      */
jaroslav@1890:     private transient Object[] queue;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The number of elements in the priority queue.
jaroslav@1890:      */
jaroslav@1890:     private transient int size;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The comparator, or null if priority queue uses elements'
jaroslav@1890:      * natural ordering.
jaroslav@1890:      */
jaroslav@1890:     private transient Comparator<? super E> comparator;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Lock used for all public operations
jaroslav@1890:      */
jaroslav@1890:     private final ReentrantLock lock;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Condition for blocking when empty
jaroslav@1890:      */
jaroslav@1890:     private final Condition notEmpty;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Spinlock for allocation, acquired via CAS.
jaroslav@1890:      */
jaroslav@1890:     private transient volatile int allocationSpinLock;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * A plain PriorityQueue used only for serialization,
jaroslav@1890:      * to maintain compatibility with previous versions
jaroslav@1890:      * of this class. Non-null only during serialization/deserialization.
jaroslav@1890:      */
jaroslav@1890:     private PriorityQueue q;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code PriorityBlockingQueue} with the default
jaroslav@1890:      * initial capacity (11) that orders its elements according to
jaroslav@1890:      * their {@linkplain Comparable natural ordering}.
jaroslav@1890:      */
jaroslav@1890:     public PriorityBlockingQueue() {
jaroslav@1890:         this(DEFAULT_INITIAL_CAPACITY, null);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code PriorityBlockingQueue} with the specified
jaroslav@1890:      * initial capacity that orders its elements according to their
jaroslav@1890:      * {@linkplain Comparable natural ordering}.
jaroslav@1890:      *
jaroslav@1890:      * @param initialCapacity the initial capacity for this priority queue
jaroslav@1890:      * @throws IllegalArgumentException if {@code initialCapacity} is less
jaroslav@1890:      *         than 1
jaroslav@1890:      */
jaroslav@1890:     public PriorityBlockingQueue(int initialCapacity) {
jaroslav@1890:         this(initialCapacity, null);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code PriorityBlockingQueue} with the specified initial
jaroslav@1890:      * capacity that orders its elements according to the specified
jaroslav@1890:      * comparator.
jaroslav@1890:      *
jaroslav@1890:      * @param initialCapacity the initial capacity for this priority queue
jaroslav@1890:      * @param  comparator the comparator that will be used to order this
jaroslav@1890:      *         priority queue.  If {@code null}, the {@linkplain Comparable
jaroslav@1890:      *         natural ordering} of the elements will be used.
jaroslav@1890:      * @throws IllegalArgumentException if {@code initialCapacity} is less
jaroslav@1890:      *         than 1
jaroslav@1890:      */
jaroslav@1890:     public PriorityBlockingQueue(int initialCapacity,
jaroslav@1890:                                  Comparator<? super E> comparator) {
jaroslav@1890:         if (initialCapacity < 1)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         this.lock = new ReentrantLock();
jaroslav@1890:         this.notEmpty = lock.newCondition();
jaroslav@1890:         this.comparator = comparator;
jaroslav@1890:         this.queue = new Object[initialCapacity];
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code PriorityBlockingQueue} containing the elements
jaroslav@1890:      * in the specified collection.  If the specified collection is a
jaroslav@1890:      * {@link SortedSet} or a {@link PriorityQueue},  this
jaroslav@1890:      * priority queue will be ordered according to the same ordering.
jaroslav@1890:      * Otherwise, this priority queue will be ordered according to the
jaroslav@1890:      * {@linkplain Comparable natural ordering} of its elements.
jaroslav@1890:      *
jaroslav@1890:      * @param  c the collection whose elements are to be placed
jaroslav@1890:      *         into this priority queue
jaroslav@1890:      * @throws ClassCastException if elements of the specified collection
jaroslav@1890:      *         cannot be compared to one another according to the priority
jaroslav@1890:      *         queue's ordering
jaroslav@1890:      * @throws NullPointerException if the specified collection or any
jaroslav@1890:      *         of its elements are null
jaroslav@1890:      */
jaroslav@1890:     public PriorityBlockingQueue(Collection<? extends E> c) {
jaroslav@1890:         this.lock = new ReentrantLock();
jaroslav@1890:         this.notEmpty = lock.newCondition();
jaroslav@1890:         boolean heapify = true; // true if not known to be in heap order
jaroslav@1890:         boolean screen = true;  // true if must screen for nulls
jaroslav@1890:         if (c instanceof SortedSet<?>) {
jaroslav@1890:             SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
jaroslav@1890:             this.comparator = (Comparator<? super E>) ss.comparator();
jaroslav@1890:             heapify = false;
jaroslav@1890:         }
jaroslav@1890:         else if (c instanceof PriorityBlockingQueue<?>) {
jaroslav@1890:             PriorityBlockingQueue<? extends E> pq =
jaroslav@1890:                 (PriorityBlockingQueue<? extends E>) c;
jaroslav@1890:             this.comparator = (Comparator<? super E>) pq.comparator();
jaroslav@1890:             screen = false;
jaroslav@1890:             if (pq.getClass() == PriorityBlockingQueue.class) // exact match
jaroslav@1890:                 heapify = false;
jaroslav@1890:         }
jaroslav@1890:         Object[] a = c.toArray();
jaroslav@1890:         int n = a.length;
jaroslav@1890:         // If c.toArray incorrectly doesn't return Object[], copy it.
jaroslav@1890:         if (a.getClass() != Object[].class)
jaroslav@1890:             a = Arrays.copyOf(a, n, Object[].class);
jaroslav@1890:         if (screen && (n == 1 || this.comparator != null)) {
jaroslav@1890:             for (int i = 0; i < n; ++i)
jaroslav@1890:                 if (a[i] == null)
jaroslav@1890:                     throw new NullPointerException();
jaroslav@1890:         }
jaroslav@1890:         this.queue = a;
jaroslav@1890:         this.size = n;
jaroslav@1890:         if (heapify)
jaroslav@1890:             heapify();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Tries to grow array to accommodate at least one more element
jaroslav@1890:      * (but normally expand by about 50%), giving up (allowing retry)
jaroslav@1890:      * on contention (which we expect to be rare). Call only while
jaroslav@1890:      * holding lock.
jaroslav@1890:      *
jaroslav@1890:      * @param array the heap array
jaroslav@1890:      * @param oldCap the length of the array
jaroslav@1890:      */
jaroslav@1890:     private void tryGrow(Object[] array, int oldCap) {
jaroslav@1890:         lock.unlock(); // must release and then re-acquire main lock
jaroslav@1890:         Object[] newArray = null;
jaroslav@1890:         if (allocationSpinLock == 0 &&
jaroslav@1890:             UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset,
jaroslav@1890:                                      0, 1)) {
jaroslav@1890:             try {
jaroslav@1890:                 int newCap = oldCap + ((oldCap < 64) ?
jaroslav@1890:                                        (oldCap + 2) : // grow faster if small
jaroslav@1890:                                        (oldCap >> 1));
jaroslav@1890:                 if (newCap - MAX_ARRAY_SIZE > 0) {    // possible overflow
jaroslav@1890:                     int minCap = oldCap + 1;
jaroslav@1890:                     if (minCap < 0 || minCap > MAX_ARRAY_SIZE)
jaroslav@1890:                         throw new OutOfMemoryError();
jaroslav@1890:                     newCap = MAX_ARRAY_SIZE;
jaroslav@1890:                 }
jaroslav@1890:                 if (newCap > oldCap && queue == array)
jaroslav@1890:                     newArray = new Object[newCap];
jaroslav@1890:             } finally {
jaroslav@1890:                 allocationSpinLock = 0;
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         if (newArray == null) // back off if another thread is allocating
jaroslav@1890:             Thread.yield();
jaroslav@1890:         lock.lock();
jaroslav@1890:         if (newArray != null && queue == array) {
jaroslav@1890:             queue = newArray;
jaroslav@1890:             System.arraycopy(array, 0, newArray, 0, oldCap);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Mechanics for poll().  Call only while holding lock.
jaroslav@1890:      */
jaroslav@1890:     private E extract() {
jaroslav@1890:         E result;
jaroslav@1890:         int n = size - 1;
jaroslav@1890:         if (n < 0)
jaroslav@1890:             result = null;
jaroslav@1890:         else {
jaroslav@1890:             Object[] array = queue;
jaroslav@1890:             result = (E) array[0];
jaroslav@1890:             E x = (E) array[n];
jaroslav@1890:             array[n] = null;
jaroslav@1890:             Comparator<? super E> cmp = comparator;
jaroslav@1890:             if (cmp == null)
jaroslav@1890:                 siftDownComparable(0, x, array, n);
jaroslav@1890:             else
jaroslav@1890:                 siftDownUsingComparator(0, x, array, n, cmp);
jaroslav@1890:             size = n;
jaroslav@1890:         }
jaroslav@1890:         return result;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts item x at position k, maintaining heap invariant by
jaroslav@1890:      * promoting x up the tree until it is greater than or equal to
jaroslav@1890:      * its parent, or is the root.
jaroslav@1890:      *
jaroslav@1890:      * To simplify and speed up coercions and comparisons. the
jaroslav@1890:      * Comparable and Comparator versions are separated into different
jaroslav@1890:      * methods that are otherwise identical. (Similarly for siftDown.)
jaroslav@1890:      * These methods are static, with heap state as arguments, to
jaroslav@1890:      * simplify use in light of possible comparator exceptions.
jaroslav@1890:      *
jaroslav@1890:      * @param k the position to fill
jaroslav@1890:      * @param x the item to insert
jaroslav@1890:      * @param array the heap array
jaroslav@1890:      * @param n heap size
jaroslav@1890:      */
jaroslav@1890:     private static <T> void siftUpComparable(int k, T x, Object[] array) {
jaroslav@1890:         Comparable<? super T> key = (Comparable<? super T>) x;
jaroslav@1890:         while (k > 0) {
jaroslav@1890:             int parent = (k - 1) >>> 1;
jaroslav@1890:             Object e = array[parent];
jaroslav@1890:             if (key.compareTo((T) e) >= 0)
jaroslav@1890:                 break;
jaroslav@1890:             array[k] = e;
jaroslav@1890:             k = parent;
jaroslav@1890:         }
jaroslav@1890:         array[k] = key;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     private static <T> void siftUpUsingComparator(int k, T x, Object[] array,
jaroslav@1890:                                        Comparator<? super T> cmp) {
jaroslav@1890:         while (k > 0) {
jaroslav@1890:             int parent = (k - 1) >>> 1;
jaroslav@1890:             Object e = array[parent];
jaroslav@1890:             if (cmp.compare(x, (T) e) >= 0)
jaroslav@1890:                 break;
jaroslav@1890:             array[k] = e;
jaroslav@1890:             k = parent;
jaroslav@1890:         }
jaroslav@1890:         array[k] = x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts item x at position k, maintaining heap invariant by
jaroslav@1890:      * demoting x down the tree repeatedly until it is less than or
jaroslav@1890:      * equal to its children or is a leaf.
jaroslav@1890:      *
jaroslav@1890:      * @param k the position to fill
jaroslav@1890:      * @param x the item to insert
jaroslav@1890:      * @param array the heap array
jaroslav@1890:      * @param n heap size
jaroslav@1890:      */
jaroslav@1890:     private static <T> void siftDownComparable(int k, T x, Object[] array,
jaroslav@1890:                                                int n) {
jaroslav@1890:         Comparable<? super T> key = (Comparable<? super T>)x;
jaroslav@1890:         int half = n >>> 1;           // loop while a non-leaf
jaroslav@1890:         while (k < half) {
jaroslav@1890:             int child = (k << 1) + 1; // assume left child is least
jaroslav@1890:             Object c = array[child];
jaroslav@1890:             int right = child + 1;
jaroslav@1890:             if (right < n &&
jaroslav@1890:                 ((Comparable<? super T>) c).compareTo((T) array[right]) > 0)
jaroslav@1890:                 c = array[child = right];
jaroslav@1890:             if (key.compareTo((T) c) <= 0)
jaroslav@1890:                 break;
jaroslav@1890:             array[k] = c;
jaroslav@1890:             k = child;
jaroslav@1890:         }
jaroslav@1890:         array[k] = key;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     private static <T> void siftDownUsingComparator(int k, T x, Object[] array,
jaroslav@1890:                                                     int n,
jaroslav@1890:                                                     Comparator<? super T> cmp) {
jaroslav@1890:         int half = n >>> 1;
jaroslav@1890:         while (k < half) {
jaroslav@1890:             int child = (k << 1) + 1;
jaroslav@1890:             Object c = array[child];
jaroslav@1890:             int right = child + 1;
jaroslav@1890:             if (right < n && cmp.compare((T) c, (T) array[right]) > 0)
jaroslav@1890:                 c = array[child = right];
jaroslav@1890:             if (cmp.compare(x, (T) c) <= 0)
jaroslav@1890:                 break;
jaroslav@1890:             array[k] = c;
jaroslav@1890:             k = child;
jaroslav@1890:         }
jaroslav@1890:         array[k] = x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Establishes the heap invariant (described above) in the entire tree,
jaroslav@1890:      * assuming nothing about the order of the elements prior to the call.
jaroslav@1890:      */
jaroslav@1890:     private void heapify() {
jaroslav@1890:         Object[] array = queue;
jaroslav@1890:         int n = size;
jaroslav@1890:         int half = (n >>> 1) - 1;
jaroslav@1890:         Comparator<? super E> cmp = comparator;
jaroslav@1890:         if (cmp == null) {
jaroslav@1890:             for (int i = half; i >= 0; i--)
jaroslav@1890:                 siftDownComparable(i, (E) array[i], array, n);
jaroslav@1890:         }
jaroslav@1890:         else {
jaroslav@1890:             for (int i = half; i >= 0; i--)
jaroslav@1890:                 siftDownUsingComparator(i, (E) array[i], array, n, cmp);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts the specified element into this priority queue.
jaroslav@1890:      *
jaroslav@1890:      * @param e the element to add
jaroslav@1890:      * @return {@code true} (as specified by {@link Collection#add})
jaroslav@1890:      * @throws ClassCastException if the specified element cannot be compared
jaroslav@1890:      *         with elements currently in the priority queue according to the
jaroslav@1890:      *         priority queue's ordering
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean add(E e) {
jaroslav@1890:         return offer(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts the specified element into this priority queue.
jaroslav@1890:      * As the queue is unbounded, this method will never return {@code false}.
jaroslav@1890:      *
jaroslav@1890:      * @param e the element to add
jaroslav@1890:      * @return {@code true} (as specified by {@link Queue#offer})
jaroslav@1890:      * @throws ClassCastException if the specified element cannot be compared
jaroslav@1890:      *         with elements currently in the priority queue according to the
jaroslav@1890:      *         priority queue's ordering
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean offer(E e) {
jaroslav@1890:         if (e == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         int n, cap;
jaroslav@1890:         Object[] array;
jaroslav@1890:         while ((n = size) >= (cap = (array = queue).length))
jaroslav@1890:             tryGrow(array, cap);
jaroslav@1890:         try {
jaroslav@1890:             Comparator<? super E> cmp = comparator;
jaroslav@1890:             if (cmp == null)
jaroslav@1890:                 siftUpComparable(n, e, array);
jaroslav@1890:             else
jaroslav@1890:                 siftUpUsingComparator(n, e, array, cmp);
jaroslav@1890:             size = n + 1;
jaroslav@1890:             notEmpty.signal();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return true;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts the specified element into this priority queue.
jaroslav@1890:      * As the queue is unbounded, this method will never block.
jaroslav@1890:      *
jaroslav@1890:      * @param e the element to add
jaroslav@1890:      * @throws ClassCastException if the specified element cannot be compared
jaroslav@1890:      *         with elements currently in the priority queue according to the
jaroslav@1890:      *         priority queue's ordering
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public void put(E e) {
jaroslav@1890:         offer(e); // never need to block
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts the specified element into this priority queue.
jaroslav@1890:      * As the queue is unbounded, this method will never block or
jaroslav@1890:      * return {@code false}.
jaroslav@1890:      *
jaroslav@1890:      * @param e the element to add
jaroslav@1890:      * @param timeout This parameter is ignored as the method never blocks
jaroslav@1890:      * @param unit This parameter is ignored as the method never blocks
jaroslav@1890:      * @return {@code true} (as specified by
jaroslav@1890:      *  {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
jaroslav@1890:      * @throws ClassCastException if the specified element cannot be compared
jaroslav@1890:      *         with elements currently in the priority queue according to the
jaroslav@1890:      *         priority queue's ordering
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean offer(E e, long timeout, TimeUnit unit) {
jaroslav@1890:         return offer(e); // never need to block
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E poll() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         E result;
jaroslav@1890:         try {
jaroslav@1890:             result = extract();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return result;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E take() throws InterruptedException {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         E result;
jaroslav@1890:         try {
jaroslav@1890:             while ( (result = extract()) == null)
jaroslav@1890:                 notEmpty.await();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return result;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E poll(long timeout, TimeUnit unit) throws InterruptedException {
jaroslav@1890:         long nanos = unit.toNanos(timeout);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         E result;
jaroslav@1890:         try {
jaroslav@1890:             while ( (result = extract()) == null && nanos > 0)
jaroslav@1890:                 nanos = notEmpty.awaitNanos(nanos);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return result;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E peek() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         E result;
jaroslav@1890:         try {
jaroslav@1890:             result = size > 0 ? (E) queue[0] : null;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return result;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the comparator used to order the elements in this queue,
jaroslav@1890:      * or {@code null} if this queue uses the {@linkplain Comparable
jaroslav@1890:      * natural ordering} of its elements.
jaroslav@1890:      *
jaroslav@1890:      * @return the comparator used to order the elements in this queue,
jaroslav@1890:      *         or {@code null} if this queue uses the natural
jaroslav@1890:      *         ordering of its elements
jaroslav@1890:      */
jaroslav@1890:     public Comparator<? super E> comparator() {
jaroslav@1890:         return comparator;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public int size() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return size;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Always returns {@code Integer.MAX_VALUE} because
jaroslav@1890:      * a {@code PriorityBlockingQueue} is not capacity constrained.
jaroslav@1890:      * @return {@code Integer.MAX_VALUE} always
jaroslav@1890:      */
jaroslav@1890:     public int remainingCapacity() {
jaroslav@1890:         return Integer.MAX_VALUE;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     private int indexOf(Object o) {
jaroslav@1890:         if (o != null) {
jaroslav@1890:             Object[] array = queue;
jaroslav@1890:             int n = size;
jaroslav@1890:             for (int i = 0; i < n; i++)
jaroslav@1890:                 if (o.equals(array[i]))
jaroslav@1890:                     return i;
jaroslav@1890:         }
jaroslav@1890:         return -1;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes the ith element from queue.
jaroslav@1890:      */
jaroslav@1890:     private void removeAt(int i) {
jaroslav@1890:         Object[] array = queue;
jaroslav@1890:         int n = size - 1;
jaroslav@1890:         if (n == i) // removed last element
jaroslav@1890:             array[i] = null;
jaroslav@1890:         else {
jaroslav@1890:             E moved = (E) array[n];
jaroslav@1890:             array[n] = null;
jaroslav@1890:             Comparator<? super E> cmp = comparator;
jaroslav@1890:             if (cmp == null)
jaroslav@1890:                 siftDownComparable(i, moved, array, n);
jaroslav@1890:             else
jaroslav@1890:                 siftDownUsingComparator(i, moved, array, n, cmp);
jaroslav@1890:             if (array[i] == moved) {
jaroslav@1890:                 if (cmp == null)
jaroslav@1890:                     siftUpComparable(i, moved, array);
jaroslav@1890:                 else
jaroslav@1890:                     siftUpUsingComparator(i, moved, array, cmp);
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:         size = n;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes a single instance of the specified element from this queue,
jaroslav@1890:      * if it is present.  More formally, removes an element {@code e} such
jaroslav@1890:      * that {@code o.equals(e)}, if this queue contains one or more such
jaroslav@1890:      * elements.  Returns {@code true} if and only if this queue contained
jaroslav@1890:      * the specified element (or equivalently, if this queue changed as a
jaroslav@1890:      * result of the call).
jaroslav@1890:      *
jaroslav@1890:      * @param o element to be removed from this queue, if present
jaroslav@1890:      * @return {@code true} if this queue changed as a result of the call
jaroslav@1890:      */
jaroslav@1890:     public boolean remove(Object o) {
jaroslav@1890:         boolean removed = false;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int i = indexOf(o);
jaroslav@1890:             if (i != -1) {
jaroslav@1890:                 removeAt(i);
jaroslav@1890:                 removed = true;
jaroslav@1890:             }
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return removed;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Identity-based version for use in Itr.remove
jaroslav@1890:      */
jaroslav@1890:     private void removeEQ(Object o) {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             Object[] array = queue;
jaroslav@1890:             int n = size;
jaroslav@1890:             for (int i = 0; i < n; i++) {
jaroslav@1890:                 if (o == array[i]) {
jaroslav@1890:                     removeAt(i);
jaroslav@1890:                     break;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this queue contains the specified element.
jaroslav@1890:      * More formally, returns {@code true} if and only if this queue contains
jaroslav@1890:      * at least one element {@code e} such that {@code o.equals(e)}.
jaroslav@1890:      *
jaroslav@1890:      * @param o object to be checked for containment in this queue
jaroslav@1890:      * @return {@code true} if this queue contains the specified element
jaroslav@1890:      */
jaroslav@1890:     public boolean contains(Object o) {
jaroslav@1890:         int index;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             index = indexOf(o);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:         return index != -1;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an array containing all of the elements in this queue.
jaroslav@1890:      * The returned array elements are in no particular order.
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned array will be "safe" in that no references to it are
jaroslav@1890:      * maintained by this queue.  (In other words, this method must allocate
jaroslav@1890:      * a new array).  The caller is thus free to modify the returned array.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method acts as bridge between array-based and collection-based
jaroslav@1890:      * APIs.
jaroslav@1890:      *
jaroslav@1890:      * @return an array containing all of the elements in this queue
jaroslav@1890:      */
jaroslav@1890:     public Object[] toArray() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return Arrays.copyOf(queue, size);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     public String toString() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = size;
jaroslav@1890:             if (n == 0)
jaroslav@1890:                 return "[]";
jaroslav@1890:             StringBuilder sb = new StringBuilder();
jaroslav@1890:             sb.append('[');
jaroslav@1890:             for (int i = 0; i < n; ++i) {
jaroslav@1890:                 E e = (E)queue[i];
jaroslav@1890:                 sb.append(e == this ? "(this Collection)" : e);
jaroslav@1890:                 if (i != n - 1)
jaroslav@1890:                     sb.append(',').append(' ');
jaroslav@1890:             }
jaroslav@1890:             return sb.append(']').toString();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws UnsupportedOperationException {@inheritDoc}
jaroslav@1890:      * @throws ClassCastException            {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException          {@inheritDoc}
jaroslav@1890:      * @throws IllegalArgumentException      {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public int drainTo(Collection<? super E> c) {
jaroslav@1890:         if (c == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (c == this)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = 0;
jaroslav@1890:             E e;
jaroslav@1890:             while ( (e = extract()) != null) {
jaroslav@1890:                 c.add(e);
jaroslav@1890:                 ++n;
jaroslav@1890:             }
jaroslav@1890:             return n;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws UnsupportedOperationException {@inheritDoc}
jaroslav@1890:      * @throws ClassCastException            {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException          {@inheritDoc}
jaroslav@1890:      * @throws IllegalArgumentException      {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public int drainTo(Collection<? super E> c, int maxElements) {
jaroslav@1890:         if (c == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (c == this)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         if (maxElements <= 0)
jaroslav@1890:             return 0;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = 0;
jaroslav@1890:             E e;
jaroslav@1890:             while (n < maxElements && (e = extract()) != null) {
jaroslav@1890:                 c.add(e);
jaroslav@1890:                 ++n;
jaroslav@1890:             }
jaroslav@1890:             return n;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Atomically removes all of the elements from this queue.
jaroslav@1890:      * The queue will be empty after this call returns.
jaroslav@1890:      */
jaroslav@1890:     public void clear() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             Object[] array = queue;
jaroslav@1890:             int n = size;
jaroslav@1890:             size = 0;
jaroslav@1890:             for (int i = 0; i < n; i++)
jaroslav@1890:                 array[i] = null;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an array containing all of the elements in this queue; the
jaroslav@1890:      * runtime type of the returned array is that of the specified array.
jaroslav@1890:      * The returned array elements are in no particular order.
jaroslav@1890:      * If the queue fits in the specified array, it is returned therein.
jaroslav@1890:      * Otherwise, a new array is allocated with the runtime type of the
jaroslav@1890:      * specified array and the size of this queue.
jaroslav@1890:      *
jaroslav@1890:      * <p>If this queue fits in the specified array with room to spare
jaroslav@1890:      * (i.e., the array has more elements than this queue), the element in
jaroslav@1890:      * the array immediately following the end of the queue is set to
jaroslav@1890:      * {@code null}.
jaroslav@1890:      *
jaroslav@1890:      * <p>Like the {@link #toArray()} method, this method acts as bridge between
jaroslav@1890:      * array-based and collection-based APIs.  Further, this method allows
jaroslav@1890:      * precise control over the runtime type of the output array, and may,
jaroslav@1890:      * under certain circumstances, be used to save allocation costs.
jaroslav@1890:      *
jaroslav@1890:      * <p>Suppose {@code x} is a queue known to contain only strings.
jaroslav@1890:      * The following code can be used to dump the queue into a newly
jaroslav@1890:      * allocated array of {@code String}:
jaroslav@1890:      *
jaroslav@1890:      * <pre>
jaroslav@1890:      *     String[] y = x.toArray(new String[0]);</pre>
jaroslav@1890:      *
jaroslav@1890:      * Note that {@code toArray(new Object[0])} is identical in function to
jaroslav@1890:      * {@code toArray()}.
jaroslav@1890:      *
jaroslav@1890:      * @param a the array into which the elements of the queue are to
jaroslav@1890:      *          be stored, if it is big enough; otherwise, a new array of the
jaroslav@1890:      *          same runtime type is allocated for this purpose
jaroslav@1890:      * @return an array containing all of the elements in this queue
jaroslav@1890:      * @throws ArrayStoreException if the runtime type of the specified array
jaroslav@1890:      *         is not a supertype of the runtime type of every element in
jaroslav@1890:      *         this queue
jaroslav@1890:      * @throws NullPointerException if the specified array is null
jaroslav@1890:      */
jaroslav@1890:     public <T> T[] toArray(T[] a) {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = size;
jaroslav@1890:             if (a.length < n)
jaroslav@1890:                 // Make a new array of a's runtime type, but my contents:
jaroslav@1890:                 return (T[]) Arrays.copyOf(queue, size, a.getClass());
jaroslav@1890:             System.arraycopy(queue, 0, a, 0, n);
jaroslav@1890:             if (a.length > n)
jaroslav@1890:                 a[n] = null;
jaroslav@1890:             return a;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an iterator over the elements in this queue. The
jaroslav@1890:      * iterator does not return the elements in any particular order.
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned iterator is a "weakly consistent" iterator that
jaroslav@1890:      * will never throw {@link java.util.ConcurrentModificationException
jaroslav@1890:      * ConcurrentModificationException}, and guarantees to traverse
jaroslav@1890:      * elements as they existed upon construction of the iterator, and
jaroslav@1890:      * may (but is not guaranteed to) reflect any modifications
jaroslav@1890:      * subsequent to construction.
jaroslav@1890:      *
jaroslav@1890:      * @return an iterator over the elements in this queue
jaroslav@1890:      */
jaroslav@1890:     public Iterator<E> iterator() {
jaroslav@1890:         return new Itr(toArray());
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Snapshot iterator that works off copy of underlying q array.
jaroslav@1890:      */
jaroslav@1890:     final class Itr implements Iterator<E> {
jaroslav@1890:         final Object[] array; // Array of all elements
jaroslav@1890:         int cursor;           // index of next element to return;
jaroslav@1890:         int lastRet;          // index of last element, or -1 if no such
jaroslav@1890: 
jaroslav@1890:         Itr(Object[] array) {
jaroslav@1890:             lastRet = -1;
jaroslav@1890:             this.array = array;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public boolean hasNext() {
jaroslav@1890:             return cursor < array.length;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public E next() {
jaroslav@1890:             if (cursor >= array.length)
jaroslav@1890:                 throw new NoSuchElementException();
jaroslav@1890:             lastRet = cursor;
jaroslav@1890:             return (E)array[cursor++];
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public void remove() {
jaroslav@1890:             if (lastRet < 0)
jaroslav@1890:                 throw new IllegalStateException();
jaroslav@1890:             removeEQ(array[lastRet]);
jaroslav@1890:             lastRet = -1;
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Saves the state to a stream (that is, serializes it).  For
jaroslav@1890:      * compatibility with previous version of this class,
jaroslav@1890:      * elements are first copied to a java.util.PriorityQueue,
jaroslav@1890:      * which is then serialized.
jaroslav@1890:      */
jaroslav@1890:     private void writeObject(java.io.ObjectOutputStream s)
jaroslav@1890:         throws java.io.IOException {
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = size; // avoid zero capacity argument
jaroslav@1890:             q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator);
jaroslav@1890:             q.addAll(this);
jaroslav@1890:             s.defaultWriteObject();
jaroslav@1890:         } finally {
jaroslav@1890:             q = null;
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Reconstitutes the {@code PriorityBlockingQueue} instance from a stream
jaroslav@1890:      * (that is, deserializes it).
jaroslav@1890:      *
jaroslav@1890:      * @param s the stream
jaroslav@1890:      */
jaroslav@1890:     private void readObject(java.io.ObjectInputStream s)
jaroslav@1890:         throws java.io.IOException, ClassNotFoundException {
jaroslav@1890:         try {
jaroslav@1890:             s.defaultReadObject();
jaroslav@1890:             this.queue = new Object[q.size()];
jaroslav@1890:             comparator = q.comparator();
jaroslav@1890:             addAll(q);
jaroslav@1890:         } finally {
jaroslav@1890:             q = null;
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Unsafe mechanics
jaroslav@1890:     private static final sun.misc.Unsafe UNSAFE;
jaroslav@1890:     private static final long allocationSpinLockOffset;
jaroslav@1890:     static {
jaroslav@1890:         try {
jaroslav@1890:             UNSAFE = sun.misc.Unsafe.getUnsafe();
jaroslav@1890:             Class k = PriorityBlockingQueue.class;
jaroslav@1890:             allocationSpinLockOffset = UNSAFE.objectFieldOffset
jaroslav@1890:                 (k.getDeclaredField("allocationSpinLock"));
jaroslav@1890:         } catch (Exception e) {
jaroslav@1890:             throw new Error(e);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: }