--- a/jdk/src/share/classes/java/util/concurrent/PriorityBlockingQueue.java Tue Jan 11 13:42:34 2011 -0800
+++ b/jdk/src/share/classes/java/util/concurrent/PriorityBlockingQueue.java Wed Jan 12 14:40:36 2011 +0000
@@ -43,11 +43,11 @@
* the same ordering rules as class {@link PriorityQueue} and supplies
* blocking retrieval operations. While this queue is logically
* unbounded, attempted additions may fail due to resource exhaustion
- * (causing <tt>OutOfMemoryError</tt>). This class does not permit
- * <tt>null</tt> elements. A priority queue relying on {@linkplain
+ * (causing {@code OutOfMemoryError}). This class does not permit
+ * {@code null} elements. A priority queue relying on {@linkplain
* Comparable natural ordering} also does not permit insertion of
* non-comparable objects (doing so results in
- * <tt>ClassCastException</tt>).
+ * {@code ClassCastException}).
*
* <p>This class and its iterator implement all of the
* <em>optional</em> methods of the {@link Collection} and {@link
@@ -55,7 +55,7 @@
* #iterator()} is <em>not</em> guaranteed to traverse the elements of
* the PriorityBlockingQueue in any particular order. If you need
* ordered traversal, consider using
- * <tt>Arrays.sort(pq.toArray())</tt>. Also, method <tt>drainTo</tt>
+ * {@code Arrays.sort(pq.toArray())}. Also, method {@code drainTo}
* can be used to <em>remove</em> some or all elements in priority
* order and place them in another collection.
*
@@ -65,12 +65,12 @@
* secondary key to break ties in primary priority values. For
* example, here is a class that applies first-in-first-out
* tie-breaking to comparable elements. To use it, you would insert a
- * <tt>new FIFOEntry(anEntry)</tt> instead of a plain entry object.
+ * {@code new FIFOEntry(anEntry)} instead of a plain entry object.
*
- * <pre>
- * class FIFOEntry<E extends Comparable<? super E>>
- * implements Comparable<FIFOEntry<E>> {
- * final static AtomicLong seq = new AtomicLong();
+ * <pre> {@code
+ * class FIFOEntry<E extends Comparable<? super E>>
+ * implements Comparable<FIFOEntry<E>> {
+ * static final AtomicLong seq = new AtomicLong(0);
* final long seqNum;
* final E entry;
* public FIFOEntry(E entry) {
@@ -78,13 +78,13 @@
* this.entry = entry;
* }
* public E getEntry() { return entry; }
- * public int compareTo(FIFOEntry<E> other) {
+ * public int compareTo(FIFOEntry<E> other) {
* int res = entry.compareTo(other.entry);
- * if (res == 0 && other.entry != this.entry)
- * res = (seqNum < other.seqNum ? -1 : 1);
+ * if (res == 0 && other.entry != this.entry)
+ * res = (seqNum < other.seqNum ? -1 : 1);
* return res;
* }
- * }</pre>
+ * }}</pre>
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
@@ -98,34 +98,102 @@
implements BlockingQueue<E>, java.io.Serializable {
private static final long serialVersionUID = 5595510919245408276L;
- private final PriorityQueue<E> q;
- private final ReentrantLock lock = new ReentrantLock(true);
- private final Condition notEmpty = lock.newCondition();
+ /*
+ * The implementation uses an array-based binary heap, with public
+ * operations protected with a single lock. However, allocation
+ * during resizing uses a simple spinlock (used only while not
+ * holding main lock) in order to allow takes to operate
+ * concurrently with allocation. This avoids repeated
+ * postponement of waiting consumers and consequent element
+ * build-up. The need to back away from lock during allocation
+ * makes it impossible to simply wrap delegated
+ * java.util.PriorityQueue operations within a lock, as was done
+ * in a previous version of this class. To maintain
+ * interoperability, a plain PriorityQueue is still used during
+ * serialization, which maintains compatibility at the espense of
+ * transiently doubling overhead.
+ */
+
+ /**
+ * Default array capacity.
+ */
+ private static final int DEFAULT_INITIAL_CAPACITY = 11;
+
+ /**
+ * The maximum size of array to allocate.
+ * Some VMs reserve some header words in an array.
+ * Attempts to allocate larger arrays may result in
+ * OutOfMemoryError: Requested array size exceeds VM limit
+ */
+ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
- * Creates a <tt>PriorityBlockingQueue</tt> with the default
+ * Priority queue represented as a balanced binary heap: the two
+ * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
+ * priority queue is ordered by comparator, or by the elements'
+ * natural ordering, if comparator is null: For each node n in the
+ * heap and each descendant d of n, n <= d. The element with the
+ * lowest value is in queue[0], assuming the queue is nonempty.
+ */
+ private transient Object[] queue;
+
+ /**
+ * The number of elements in the priority queue.
+ */
+ private transient int size;
+
+ /**
+ * The comparator, or null if priority queue uses elements'
+ * natural ordering.
+ */
+ private transient Comparator<? super E> comparator;
+
+ /**
+ * Lock used for all public operations
+ */
+ private final ReentrantLock lock;
+
+ /**
+ * Condition for blocking when empty
+ */
+ private final Condition notEmpty;
+
+ /**
+ * Spinlock for allocation, acquired via CAS.
+ */
+ private transient volatile int allocationSpinLock;
+
+ /**
+ * A plain PriorityQueue used only for serialization,
+ * to maintain compatibility with previous versions
+ * of this class. Non-null only during serialization/deserialization.
+ */
+ private PriorityQueue q;
+
+ /**
+ * Creates a {@code PriorityBlockingQueue} with the default
* initial capacity (11) that orders its elements according to
* their {@linkplain Comparable natural ordering}.
*/
public PriorityBlockingQueue() {
- q = new PriorityQueue<E>();
+ this(DEFAULT_INITIAL_CAPACITY, null);
}
/**
- * Creates a <tt>PriorityBlockingQueue</tt> with the specified
+ * Creates a {@code PriorityBlockingQueue} with the specified
* initial capacity that orders its elements according to their
* {@linkplain Comparable natural ordering}.
*
* @param initialCapacity the initial capacity for this priority queue
- * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
+ * @throws IllegalArgumentException if {@code initialCapacity} is less
* than 1
*/
public PriorityBlockingQueue(int initialCapacity) {
- q = new PriorityQueue<E>(initialCapacity, null);
+ this(initialCapacity, null);
}
/**
- * Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
+ * Creates a {@code PriorityBlockingQueue} with the specified initial
* capacity that orders its elements according to the specified
* comparator.
*
@@ -133,16 +201,21 @@
* @param comparator the comparator that will be used to order this
* priority queue. If {@code null}, the {@linkplain Comparable
* natural ordering} of the elements will be used.
- * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
+ * @throws IllegalArgumentException if {@code initialCapacity} is less
* than 1
*/
public PriorityBlockingQueue(int initialCapacity,
Comparator<? super E> comparator) {
- q = new PriorityQueue<E>(initialCapacity, comparator);
+ if (initialCapacity < 1)
+ throw new IllegalArgumentException();
+ this.lock = new ReentrantLock();
+ this.notEmpty = lock.newCondition();
+ this.comparator = comparator;
+ this.queue = new Object[initialCapacity];
}
/**
- * Creates a <tt>PriorityBlockingQueue</tt> containing the elements
+ * Creates a {@code PriorityBlockingQueue} containing the elements
* in the specified collection. If the specified collection is a
* {@link SortedSet} or a {@link PriorityQueue}, this
* priority queue will be ordered according to the same ordering.
@@ -158,14 +231,215 @@
* of its elements are null
*/
public PriorityBlockingQueue(Collection<? extends E> c) {
- q = new PriorityQueue<E>(c);
+ this.lock = new ReentrantLock();
+ this.notEmpty = lock.newCondition();
+ boolean heapify = true; // true if not known to be in heap order
+ boolean screen = true; // true if must screen for nulls
+ if (c instanceof SortedSet<?>) {
+ SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
+ this.comparator = (Comparator<? super E>) ss.comparator();
+ heapify = false;
+ }
+ else if (c instanceof PriorityBlockingQueue<?>) {
+ PriorityBlockingQueue<? extends E> pq =
+ (PriorityBlockingQueue<? extends E>) c;
+ this.comparator = (Comparator<? super E>) pq.comparator();
+ screen = false;
+ if (pq.getClass() == PriorityBlockingQueue.class) // exact match
+ heapify = false;
+ }
+ Object[] a = c.toArray();
+ int n = a.length;
+ // If c.toArray incorrectly doesn't return Object[], copy it.
+ if (a.getClass() != Object[].class)
+ a = Arrays.copyOf(a, n, Object[].class);
+ if (screen && (n == 1 || this.comparator != null)) {
+ for (int i = 0; i < n; ++i)
+ if (a[i] == null)
+ throw new NullPointerException();
+ }
+ this.queue = a;
+ this.size = n;
+ if (heapify)
+ heapify();
+ }
+
+ /**
+ * Tries to grow array to accommodate at least one more element
+ * (but normally expand by about 50%), giving up (allowing retry)
+ * on contention (which we expect to be rare). Call only while
+ * holding lock.
+ *
+ * @param array the heap array
+ * @param oldCap the length of the array
+ */
+ private void tryGrow(Object[] array, int oldCap) {
+ lock.unlock(); // must release and then re-acquire main lock
+ Object[] newArray = null;
+ if (allocationSpinLock == 0 &&
+ UNSAFE.compareAndSwapInt(this, allocationSpinLockOffset,
+ 0, 1)) {
+ try {
+ int newCap = oldCap + ((oldCap < 64) ?
+ (oldCap + 2) : // grow faster if small
+ (oldCap >> 1));
+ if (newCap - MAX_ARRAY_SIZE > 0) { // possible overflow
+ int minCap = oldCap + 1;
+ if (minCap < 0 || minCap > MAX_ARRAY_SIZE)
+ throw new OutOfMemoryError();
+ newCap = MAX_ARRAY_SIZE;
+ }
+ if (newCap > oldCap && queue == array)
+ newArray = new Object[newCap];
+ } finally {
+ allocationSpinLock = 0;
+ }
+ }
+ if (newArray == null) // back off if another thread is allocating
+ Thread.yield();
+ lock.lock();
+ if (newArray != null && queue == array) {
+ queue = newArray;
+ System.arraycopy(array, 0, newArray, 0, oldCap);
+ }
+ }
+
+ /**
+ * Mechanics for poll(). Call only while holding lock.
+ */
+ private E extract() {
+ E result;
+ int n = size - 1;
+ if (n < 0)
+ result = null;
+ else {
+ Object[] array = queue;
+ result = (E) array[0];
+ E x = (E) array[n];
+ array[n] = null;
+ Comparator<? super E> cmp = comparator;
+ if (cmp == null)
+ siftDownComparable(0, x, array, n);
+ else
+ siftDownUsingComparator(0, x, array, n, cmp);
+ size = n;
+ }
+ return result;
+ }
+
+ /**
+ * Inserts item x at position k, maintaining heap invariant by
+ * promoting x up the tree until it is greater than or equal to
+ * its parent, or is the root.
+ *
+ * To simplify and speed up coercions and comparisons. the
+ * Comparable and Comparator versions are separated into different
+ * methods that are otherwise identical. (Similarly for siftDown.)
+ * These methods are static, with heap state as arguments, to
+ * simplify use in light of possible comparator exceptions.
+ *
+ * @param k the position to fill
+ * @param x the item to insert
+ * @param array the heap array
+ * @param n heap size
+ */
+ private static <T> void siftUpComparable(int k, T x, Object[] array) {
+ Comparable<? super T> key = (Comparable<? super T>) x;
+ while (k > 0) {
+ int parent = (k - 1) >>> 1;
+ Object e = array[parent];
+ if (key.compareTo((T) e) >= 0)
+ break;
+ array[k] = e;
+ k = parent;
+ }
+ array[k] = key;
+ }
+
+ private static <T> void siftUpUsingComparator(int k, T x, Object[] array,
+ Comparator<? super T> cmp) {
+ while (k > 0) {
+ int parent = (k - 1) >>> 1;
+ Object e = array[parent];
+ if (cmp.compare(x, (T) e) >= 0)
+ break;
+ array[k] = e;
+ k = parent;
+ }
+ array[k] = x;
+ }
+
+ /**
+ * Inserts item x at position k, maintaining heap invariant by
+ * demoting x down the tree repeatedly until it is less than or
+ * equal to its children or is a leaf.
+ *
+ * @param k the position to fill
+ * @param x the item to insert
+ * @param array the heap array
+ * @param n heap size
+ */
+ private static <T> void siftDownComparable(int k, T x, Object[] array,
+ int n) {
+ Comparable<? super T> key = (Comparable<? super T>)x;
+ int half = n >>> 1; // loop while a non-leaf
+ while (k < half) {
+ int child = (k << 1) + 1; // assume left child is least
+ Object c = array[child];
+ int right = child + 1;
+ if (right < n &&
+ ((Comparable<? super T>) c).compareTo((T) array[right]) > 0)
+ c = array[child = right];
+ if (key.compareTo((T) c) <= 0)
+ break;
+ array[k] = c;
+ k = child;
+ }
+ array[k] = key;
+ }
+
+ private static <T> void siftDownUsingComparator(int k, T x, Object[] array,
+ int n,
+ Comparator<? super T> cmp) {
+ int half = n >>> 1;
+ while (k < half) {
+ int child = (k << 1) + 1;
+ Object c = array[child];
+ int right = child + 1;
+ if (right < n && cmp.compare((T) c, (T) array[right]) > 0)
+ c = array[child = right];
+ if (cmp.compare(x, (T) c) <= 0)
+ break;
+ array[k] = c;
+ k = child;
+ }
+ array[k] = x;
+ }
+
+ /**
+ * Establishes the heap invariant (described above) in the entire tree,
+ * assuming nothing about the order of the elements prior to the call.
+ */
+ private void heapify() {
+ Object[] array = queue;
+ int n = size;
+ int half = (n >>> 1) - 1;
+ Comparator<? super E> cmp = comparator;
+ if (cmp == null) {
+ for (int i = half; i >= 0; i--)
+ siftDownComparable(i, (E) array[i], array, n);
+ }
+ else {
+ for (int i = half; i >= 0; i--)
+ siftDownUsingComparator(i, (E) array[i], array, n, cmp);
+ }
}
/**
* Inserts the specified element into this priority queue.
*
* @param e the element to add
- * @return <tt>true</tt> (as specified by {@link Collection#add})
+ * @return {@code true} (as specified by {@link Collection#add})
* @throws ClassCastException if the specified element cannot be compared
* with elements currently in the priority queue according to the
* priority queue's ordering
@@ -177,30 +451,41 @@
/**
* Inserts the specified element into this priority queue.
+ * As the queue is unbounded, this method will never return {@code false}.
*
* @param e the element to add
- * @return <tt>true</tt> (as specified by {@link Queue#offer})
+ * @return {@code true} (as specified by {@link Queue#offer})
* @throws ClassCastException if the specified element cannot be compared
* with elements currently in the priority queue according to the
* priority queue's ordering
* @throws NullPointerException if the specified element is null
*/
public boolean offer(E e) {
+ if (e == null)
+ throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
+ int n, cap;
+ Object[] array;
+ while ((n = size) >= (cap = (array = queue).length))
+ tryGrow(array, cap);
try {
- boolean ok = q.offer(e);
- assert ok;
+ Comparator<? super E> cmp = comparator;
+ if (cmp == null)
+ siftUpComparable(n, e, array);
+ else
+ siftUpUsingComparator(n, e, array, cmp);
+ size = n + 1;
notEmpty.signal();
- return true;
} finally {
lock.unlock();
}
+ return true;
}
/**
- * Inserts the specified element into this priority queue. As the queue is
- * unbounded this method will never block.
+ * Inserts the specified element into this priority queue.
+ * As the queue is unbounded, this method will never block.
*
* @param e the element to add
* @throws ClassCastException if the specified element cannot be compared
@@ -213,13 +498,15 @@
}
/**
- * Inserts the specified element into this priority queue. As the queue is
- * unbounded this method will never block.
+ * Inserts the specified element into this priority queue.
+ * As the queue is unbounded, this method will never block or
+ * return {@code false}.
*
* @param e the element to add
* @param timeout This parameter is ignored as the method never blocks
* @param unit This parameter is ignored as the method never blocks
- * @return <tt>true</tt>
+ * @return {@code true} (as specified by
+ * {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
* @throws ClassCastException if the specified element cannot be compared
* with elements currently in the priority queue according to the
* priority queue's ordering
@@ -232,95 +519,121 @@
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
+ E result;
try {
- return q.poll();
+ result = extract();
} finally {
lock.unlock();
}
+ return result;
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
+ E result;
try {
- try {
- while (q.size() == 0)
- notEmpty.await();
- } catch (InterruptedException ie) {
- notEmpty.signal(); // propagate to non-interrupted thread
- throw ie;
- }
- E x = q.poll();
- assert x != null;
- return x;
+ while ( (result = extract()) == null)
+ notEmpty.await();
} finally {
lock.unlock();
}
+ return result;
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
+ E result;
try {
- for (;;) {
- E x = q.poll();
- if (x != null)
- return x;
- if (nanos <= 0)
- return null;
- try {
- nanos = notEmpty.awaitNanos(nanos);
- } catch (InterruptedException ie) {
- notEmpty.signal(); // propagate to non-interrupted thread
- throw ie;
- }
- }
+ while ( (result = extract()) == null && nanos > 0)
+ nanos = notEmpty.awaitNanos(nanos);
} finally {
lock.unlock();
}
+ return result;
}
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
+ E result;
try {
- return q.peek();
+ result = size > 0 ? (E) queue[0] : null;
+ } finally {
+ lock.unlock();
+ }
+ return result;
+ }
+
+ /**
+ * Returns the comparator used to order the elements in this queue,
+ * or {@code null} if this queue uses the {@linkplain Comparable
+ * natural ordering} of its elements.
+ *
+ * @return the comparator used to order the elements in this queue,
+ * or {@code null} if this queue uses the natural
+ * ordering of its elements
+ */
+ public Comparator<? super E> comparator() {
+ return comparator;
+ }
+
+ public int size() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ return size;
} finally {
lock.unlock();
}
}
/**
- * Returns the comparator used to order the elements in this queue,
- * or <tt>null</tt> if this queue uses the {@linkplain Comparable
- * natural ordering} of its elements.
- *
- * @return the comparator used to order the elements in this queue,
- * or <tt>null</tt> if this queue uses the natural
- * ordering of its elements
+ * Always returns {@code Integer.MAX_VALUE} because
+ * a {@code PriorityBlockingQueue} is not capacity constrained.
+ * @return {@code Integer.MAX_VALUE} always
*/
- public Comparator<? super E> comparator() {
- return q.comparator();
+ public int remainingCapacity() {
+ return Integer.MAX_VALUE;
}
- public int size() {
- final ReentrantLock lock = this.lock;
- lock.lock();
- try {
- return q.size();
- } finally {
- lock.unlock();
+ private int indexOf(Object o) {
+ if (o != null) {
+ Object[] array = queue;
+ int n = size;
+ for (int i = 0; i < n; i++)
+ if (o.equals(array[i]))
+ return i;
}
+ return -1;
}
/**
- * Always returns <tt>Integer.MAX_VALUE</tt> because
- * a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
- * @return <tt>Integer.MAX_VALUE</tt>
+ * Removes the ith element from queue.
*/
- public int remainingCapacity() {
- return Integer.MAX_VALUE;
+ private void removeAt(int i) {
+ Object[] array = queue;
+ int n = size - 1;
+ if (n == i) // removed last element
+ array[i] = null;
+ else {
+ E moved = (E) array[n];
+ array[n] = null;
+ Comparator<? super E> cmp = comparator;
+ if (cmp == null)
+ siftDownComparable(i, moved, array, n);
+ else
+ siftDownUsingComparator(i, moved, array, n, cmp);
+ if (array[i] == moved) {
+ if (cmp == null)
+ siftUpComparable(i, moved, array);
+ else
+ siftUpUsingComparator(i, moved, array, cmp);
+ }
+ }
+ size = n;
}
/**
@@ -332,13 +645,40 @@
* result of the call).
*
* @param o element to be removed from this queue, if present
- * @return <tt>true</tt> if this queue changed as a result of the call
+ * @return {@code true} if this queue changed as a result of the call
*/
public boolean remove(Object o) {
+ boolean removed = false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return q.remove(o);
+ int i = indexOf(o);
+ if (i != -1) {
+ removeAt(i);
+ removed = true;
+ }
+ } finally {
+ lock.unlock();
+ }
+ return removed;
+ }
+
+
+ /**
+ * Identity-based version for use in Itr.remove
+ */
+ private void removeEQ(Object o) {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ Object[] array = queue;
+ int n = size;
+ for (int i = 0; i < n; i++) {
+ if (o == array[i]) {
+ removeAt(i);
+ break;
+ }
+ }
} finally {
lock.unlock();
}
@@ -350,16 +690,18 @@
* at least one element {@code e} such that {@code o.equals(e)}.
*
* @param o object to be checked for containment in this queue
- * @return <tt>true</tt> if this queue contains the specified element
+ * @return {@code true} if this queue contains the specified element
*/
public boolean contains(Object o) {
+ int index;
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return q.contains(o);
+ index = indexOf(o);
} finally {
lock.unlock();
}
+ return index != -1;
}
/**
@@ -379,7 +721,7 @@
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return q.toArray();
+ return Arrays.copyOf(queue, size);
} finally {
lock.unlock();
}
@@ -390,7 +732,18 @@
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return q.toString();
+ int n = size;
+ if (n == 0)
+ return "[]";
+ StringBuilder sb = new StringBuilder();
+ sb.append('[');
+ for (int i = 0; i < n; ++i) {
+ E e = (E)queue[i];
+ sb.append(e == this ? "(this Collection)" : e);
+ if (i != n - 1)
+ sb.append(',').append(' ');
+ }
+ return sb.append(']').toString();
} finally {
lock.unlock();
}
@@ -412,7 +765,7 @@
try {
int n = 0;
E e;
- while ( (e = q.poll()) != null) {
+ while ( (e = extract()) != null) {
c.add(e);
++n;
}
@@ -440,7 +793,7 @@
try {
int n = 0;
E e;
- while (n < maxElements && (e = q.poll()) != null) {
+ while (n < maxElements && (e = extract()) != null) {
c.add(e);
++n;
}
@@ -458,7 +811,11 @@
final ReentrantLock lock = this.lock;
lock.lock();
try {
- q.clear();
+ Object[] array = queue;
+ int n = size;
+ size = 0;
+ for (int i = 0; i < n; i++)
+ array[i] = null;
} finally {
lock.unlock();
}
@@ -475,22 +832,22 @@
* <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
- * <tt>null</tt>.
+ * {@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 <tt>x</tt> is a queue known to contain only strings.
+ * <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 <tt>String</tt>:
+ * allocated array of {@code String}:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
- * Note that <tt>toArray(new Object[0])</tt> is identical in function to
- * <tt>toArray()</tt>.
+ * 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
@@ -505,7 +862,14 @@
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return q.toArray(a);
+ int n = size;
+ if (a.length < n)
+ // Make a new array of a's runtime type, but my contents:
+ return (T[]) Arrays.copyOf(queue, size, a.getClass());
+ System.arraycopy(queue, 0, a, 0, n);
+ if (a.length > n)
+ a[n] = null;
+ return a;
} finally {
lock.unlock();
}
@@ -514,8 +878,9 @@
/**
* Returns an iterator over the elements in this queue. The
* iterator does not return the elements in any particular order.
- * The returned <tt>Iterator</tt> is a "weakly consistent"
- * iterator that will never throw {@link
+ *
+ * <p>The returned iterator is a "weakly consistent" iterator that
+ * will never throw {@link java.util.ConcurrentModificationException
* ConcurrentModificationException}, and guarantees to traverse
* elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications
@@ -530,7 +895,7 @@
/**
* Snapshot iterator that works off copy of underlying q array.
*/
- private class Itr implements Iterator<E> {
+ final class Itr implements Iterator<E> {
final Object[] array; // Array of all elements
int cursor; // index of next element to return;
int lastRet; // index of last element, or -1 if no such
@@ -554,39 +919,65 @@
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
- Object x = array[lastRet];
+ removeEQ(array[lastRet]);
lastRet = -1;
- // Traverse underlying queue to find == element,
- // not just a .equals element.
- lock.lock();
- try {
- for (Iterator it = q.iterator(); it.hasNext(); ) {
- if (it.next() == x) {
- it.remove();
- return;
- }
- }
- } finally {
- lock.unlock();
- }
}
}
/**
- * Saves the state to a stream (that is, serializes it). This
- * merely wraps default serialization within lock. The
- * serialization strategy for items is left to underlying
- * Queue. Note that locking is not needed on deserialization, so
- * readObject is not defined, just relying on default.
+ * Saves the state to a stream (that is, serializes it). For
+ * compatibility with previous version of this class,
+ * elements are first copied to a java.util.PriorityQueue,
+ * which is then serialized.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
lock.lock();
try {
+ int n = size; // avoid zero capacity argument
+ q = new PriorityQueue<E>(n == 0 ? 1 : n, comparator);
+ q.addAll(this);
s.defaultWriteObject();
} finally {
+ q = null;
lock.unlock();
}
}
+ /**
+ * Reconstitutes the {@code PriorityBlockingQueue} instance from a stream
+ * (that is, deserializes it).
+ *
+ * @param s the stream
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ try {
+ s.defaultReadObject();
+ this.queue = new Object[q.size()];
+ comparator = q.comparator();
+ addAll(q);
+ } finally {
+ q = null;
+ }
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+ private static final long allocationSpinLockOffset =
+ objectFieldOffset(UNSAFE, "allocationSpinLock",
+ PriorityBlockingQueue.class);
+
+ static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
+ String field, Class<?> klazz) {
+ try {
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to corresponding Error
+ NoSuchFieldError error = new NoSuchFieldError(field);
+ error.initCause(e);
+ throw error;
+ }
+ }
+
}