/*
* 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/licenses/publicdomain
*/
package java.util.concurrent;
import java.util.concurrent.locks.*;
import java.util.*;
/**
* An unbounded {@linkplain BlockingQueue blocking queue} that uses
* 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
* Comparable natural ordering} also does not permit insertion of
* non-comparable objects (doing so results in
* <tt>ClassCastException</tt>).
*
* <p>This class and its iterator implement all of the
* <em>optional</em> methods of the {@link Collection} and {@link
* Iterator} interfaces. The Iterator provided in method {@link
* #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>
* can be used to <em>remove</em> some or all elements in priority
* order and place them in another collection.
*
* <p>Operations on this class make no guarantees about the ordering
* of elements with equal priority. If you need to enforce an
* ordering, you can define custom classes or comparators that use a
* 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.
*
* <pre>
* class FIFOEntry<E extends Comparable<? super E>>
* implements Comparable<FIFOEntry<E>> {
* final static AtomicLong seq = new AtomicLong();
* final long seqNum;
* final E entry;
* public FIFOEntry(E entry) {
* seqNum = seq.getAndIncrement();
* this.entry = entry;
* }
* public E getEntry() { return entry; }
* 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);
* return res;
* }
* }</pre>
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @since 1.5
* @author Doug Lea
* @param <E> the type of elements held in this collection
*/
public class PriorityBlockingQueue<E> extends AbstractQueue<E>
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();
/**
* Creates a <tt>PriorityBlockingQueue</tt> with the default
* initial capacity (11) that orders its elements according to
* their {@linkplain Comparable natural ordering}.
*/
public PriorityBlockingQueue() {
q = new PriorityQueue<E>();
}
/**
* Creates a <tt>PriorityBlockingQueue</tt> 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
* than 1
*/
public PriorityBlockingQueue(int initialCapacity) {
q = new PriorityQueue<E>(initialCapacity, null);
}
/**
* Creates a <tt>PriorityBlockingQueue</tt> with the specified initial
* capacity that orders its elements according to the specified
* comparator.
*
* @param initialCapacity the initial capacity for this priority queue
* @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
* than 1
*/
public PriorityBlockingQueue(int initialCapacity,
Comparator<? super E> comparator) {
q = new PriorityQueue<E>(initialCapacity, comparator);
}
/**
* Creates a <tt>PriorityBlockingQueue</tt> 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.
* Otherwise, this priority queue will be ordered according to the
* {@linkplain Comparable natural ordering} of its elements.
*
* @param c the collection whose elements are to be placed
* into this priority queue
* @throws ClassCastException if elements of the specified collection
* cannot be compared to one another according to the priority
* queue's ordering
* @throws NullPointerException if the specified collection or any
* of its elements are null
*/
public PriorityBlockingQueue(Collection<? extends E> c) {
q = new PriorityQueue<E>(c);
}
/**
* Inserts the specified element into this priority queue.
*
* @param e the element to add
* @return <tt>true</tt> (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
* @throws NullPointerException if the specified element is null
*/
public boolean add(E e) {
return offer(e);
}
/**
* Inserts the specified element into this priority queue.
*
* @param e the element to add
* @return <tt>true</tt> (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) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
boolean ok = q.offer(e);
assert ok;
notEmpty.signal();
return true;
} finally {
lock.unlock();
}
}
/**
* 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
* with elements currently in the priority queue according to the
* priority queue's ordering
* @throws NullPointerException if the specified element is null
*/
public void put(E e) {
offer(e); // never need to 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
* @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>
* @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, long timeout, TimeUnit unit) {
return offer(e); // never need to block
}
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.poll();
} finally {
lock.unlock();
}
}
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
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;
} finally {
lock.unlock();
}
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
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;
}
}
} finally {
lock.unlock();
}
}
public E peek() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.peek();
} 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
*/
public Comparator<? super E> comparator() {
return q.comparator();
}
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.size();
} finally {
lock.unlock();
}
}
/**
* Always returns <tt>Integer.MAX_VALUE</tt> because
* a <tt>PriorityBlockingQueue</tt> is not capacity constrained.
* @return <tt>Integer.MAX_VALUE</tt>
*/
public int remainingCapacity() {
return Integer.MAX_VALUE;
}
/**
* 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 and only if this queue contained
* the specified element (or equivalently, if this queue changed as a
* result of the call).
*
* @param o element to be removed from this queue, if present
* @return <tt>true</tt> if this queue changed as a result of the call
*/
public boolean remove(Object o) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.remove(o);
} finally {
lock.unlock();
}
}
/**
* 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 <tt>true</tt> if this queue contains the specified element
*/
public boolean contains(Object o) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.contains(o);
} finally {
lock.unlock();
}
}
/**
* Returns an array containing all of the elements in this queue.
* The returned array elements are in no particular order.
*
* <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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.toArray();
} finally {
lock.unlock();
}
}
public String toString() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.toString();
} finally {
lock.unlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = 0;
E e;
while ( (e = q.poll()) != null) {
c.add(e);
++n;
}
return n;
} finally {
lock.unlock();
}
}
/**
* @throws UnsupportedOperationException {@inheritDoc}
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c, int maxElements) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
if (maxElements <= 0)
return 0;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = 0;
E e;
while (n < maxElements && (e = q.poll()) != null) {
c.add(e);
++n;
}
return n;
} finally {
lock.unlock();
}
}
/**
* Atomically removes all of the elements from this queue.
* The queue will be empty after this call returns.
*/
public void clear() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
q.clear();
} finally {
lock.unlock();
}
}
/**
* Returns an array containing all of the elements in this queue; the
* runtime type of the returned array is that of the specified array.
* The returned array elements are in no particular order.
* 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
* <tt>null</tt>.
*
* <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.
* The following code can be used to dump the queue into a newly
* allocated array of <tt>String</tt>:
*
* <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>.
*
* @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
*/
public <T> T[] toArray(T[] a) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return q.toArray(a);
} finally {
lock.unlock();
}
}
/**
* 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
* ConcurrentModificationException}, and guarantees to traverse
* elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications
* subsequent to construction.
*
* @return an iterator over the elements in this queue
*/
public Iterator<E> iterator() {
return new Itr(toArray());
}
/**
* Snapshot iterator that works off copy of underlying q array.
*/
private 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
Itr(Object[] array) {
lastRet = -1;
this.array = array;
}
public boolean hasNext() {
return cursor < array.length;
}
public E next() {
if (cursor >= array.length)
throw new NoSuchElementException();
lastRet = cursor;
return (E)array[cursor++];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
Object x = 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.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
lock.lock();
try {
s.defaultWriteObject();
} finally {
lock.unlock();
}
}
}