| /* |
| * 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(); |
| } |
| } |
| |
| } |