/* * Copyright (C) 2010 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.util.concurrent; import static com.google.common.base.Preconditions.checkNotNull; import java.util.AbstractQueue; import java.util.Collection; import java.util.Comparator; import java.util.ConcurrentModificationException; import java.util.Iterator; import java.util.NoSuchElementException; import java.util.PriorityQueue; import java.util.Queue; import java.util.SortedSet; import java.util.concurrent.BlockingQueue; import java.util.concurrent.TimeUnit; import javax.annotation.Nullable; /** * 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 OutOfMemoryError). This class does not permit * null elements. A priority queue relying on {@linkplain * Comparable natural ordering} also does not permit insertion of * non-comparable objects (doing so results in * ClassCastException). * *
This class and its iterator implement all of the * optional methods of the {@link Collection} and {@link * Iterator} interfaces. The Iterator provided in method {@link * #iterator()} is not guaranteed to traverse the elements of * the MonitorBasedPriorityBlockingQueue in any particular order. If you need * ordered traversal, consider using * Arrays.sort(pq.toArray()). Also, method drainTo * can be used to remove some or all elements in priority * order and place them in another collection. * *
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 * new FIFOEntry(anEntry) instead of a plain entry object. * *
* 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; * } * }* * @author Doug Lea * @author Justin T. Sampson * @param
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. * *
This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all of the elements in this queue */ @Override public Object[] toArray() { final Monitor monitor = this.monitor; monitor.enter(); try { return q.toArray(); } finally { monitor.leave(); } } @Override public String toString() { final Monitor monitor = this.monitor; monitor.enter(); try { return q.toString(); } finally { monitor.leave(); } } /** * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} */ @Override public int drainTo(Collection super E> c) { if (c == null) throw new NullPointerException(); if (c == this) throw new IllegalArgumentException(); final Monitor monitor = this.monitor; monitor.enter(); try { int n = 0; E e; while ( (e = q.poll()) != null) { c.add(e); ++n; } return n; } finally { monitor.leave(); } } /** * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} */ @Override 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 Monitor monitor = this.monitor; monitor.enter(); try { int n = 0; E e; while (n < maxElements && (e = q.poll()) != null) { c.add(e); ++n; } return n; } finally { monitor.leave(); } } /** * Atomically removes all of the elements from this queue. * The queue will be empty after this call returns. */ @Override public void clear() { final Monitor monitor = this.monitor; monitor.enter(); try { q.clear(); } finally { monitor.leave(); } } /** * 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. * *
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 * null. * *
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. * *
Suppose 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 String: * *
* String[] y = x.toArray(new String[0]);* *
Note that toArray(new Object[0]) is identical in function to
* toArray().
*
* @param a the array into which the elements of the queue are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose
* @return an array containing all of the elements in this queue
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this queue
* @throws NullPointerException if the specified array is null
*/
@Override public