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/* * @(#)DelayQueue.java 1.14 06/04/21 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.concurrent; import java.util.concurrent.locks.*; import java.util.*; /** * An unbounded {@linkplain BlockingQueue blocking queue} of * <tt>Delayed</tt> elements, in which an element can only be taken * when its delay has expired. The <em>head</em> of the queue is that * <tt>Delayed</tt> element whose delay expired furthest in the * past. If no delay has expired there is no head and <tt>poll</tt> * will return <tt>null</tt>. Expiration occurs when an element's * <tt>getDelay(TimeUnit.NANOSECONDS)</tt> method returns a value less * than or equal to zero. Even though unexpired elements cannot be * removed using <tt>take</tt> or <tt>poll</tt>, they are otherwise * treated as normal elements. For example, the <tt>size</tt> method * returns the count of both expired and unexpired elements. * This queue does not permit null elements. * * <p>This class and its iterator implement all of the * <em>optional</em> methods of the {@link Collection} and {@link * Iterator} interfaces. * * <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 DelayQueue<E extends Delayed> extends AbstractQueue<E> implements BlockingQueue<E> { private transient final ReentrantLock lock = new ReentrantLock(); private transient final Condition available = lock.newCondition(); private final PriorityQueue<E> q = new PriorityQueue<E>(); /** * Creates a new <tt>DelayQueue</tt> that is initially empty. */ public DelayQueue() {} /** * Creates a <tt>DelayQueue</tt> initially containing the elements of the * given collection of {@link Delayed} instances. * * @param c the collection of elements to initially contain * @throws NullPointerException if the specified collection or any * of its elements are null */ public DelayQueue(Collection<? extends E> c) { this.addAll(c); } /** * Inserts the specified element into this delay queue. * * @param e the element to add * @return <tt>true</tt> (as specified by {@link Collection#add}) * @throws NullPointerException if the specified element is null */ public boolean add(E e) { return offer(e); } /** * Inserts the specified element into this delay queue. * * @param e the element to add * @return <tt>true</tt> * @throws NullPointerException if the specified element is null */ public boolean offer(E e) { final ReentrantLock lock = this.lock; lock.lock(); try { E first = q.peek(); q.offer(e); if (first == null || e.compareTo(first) < 0) available.signalAll(); return true; } finally { lock.unlock(); } } /** * Inserts the specified element into this delay queue. As the queue is * unbounded this method will never block. * * @param e the element to add * @throws NullPointerException {@inheritDoc} */ public void put(E e) { offer(e); } /** * Inserts the specified element into this delay 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 NullPointerException {@inheritDoc} */ public boolean offer(E e, long timeout, TimeUnit unit) { return offer(e); } /** * Retrieves and removes the head of this queue, or returns <tt>null</tt> * if this queue has no elements with an expired delay. * * @return the head of this queue, or <tt>null</tt> if this * queue has no elements with an expired delay */ public E poll() { final ReentrantLock lock = this.lock; lock.lock(); try { E first = q.peek(); if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) return null; else { E x = q.poll(); assert x != null; if (q.size() != 0) available.signalAll(); return x; } } finally { lock.unlock(); } } /** * Retrieves and removes the head of this queue, waiting if necessary * until an element with an expired delay is available on this queue. * * @return the head of this queue * @throws InterruptedException {@inheritDoc} */ public E take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { for (;;) { E first = q.peek(); if (first == null) { available.await(); } else { long delay = first.getDelay(TimeUnit.NANOSECONDS); if (delay > 0) { long tl = available.awaitNanos(delay); } else { E x = q.poll(); assert x != null; if (q.size() != 0) available.signalAll(); // wake up other takers return x; } } } } finally { lock.unlock(); } } /** * Retrieves and removes the head of this queue, waiting if necessary * until an element with an expired delay is available on this queue, * or the specified wait time expires. * * @return the head of this queue, or <tt>null</tt> if the * specified waiting time elapses before an element with * an expired delay becomes available * @throws InterruptedException {@inheritDoc} */ public E poll(long timeout, TimeUnit unit) throws InterruptedException { long nanos = unit.toNanos(timeout); final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { for (;;) { E first = q.peek(); if (first == null) { if (nanos <= 0) return null; else nanos = available.awaitNanos(nanos); } else { long delay = first.getDelay(TimeUnit.NANOSECONDS); if (delay > 0) { if (nanos <= 0) return null; if (delay > nanos) delay = nanos; long timeLeft = available.awaitNanos(delay); nanos -= delay - timeLeft; } else { E x = q.poll(); assert x != null; if (q.size() != 0) available.signalAll(); return x; } } } } finally { lock.unlock(); } } /** * Retrieves, but does not remove, the head of this queue, or * returns <tt>null</tt> if this queue is empty. Unlike * <tt>poll</tt>, if no expired elements are available in the queue, * this method returns the element that will expire next, * if one exists. * * @return the head of this queue, or <tt>null</tt> if this * queue is empty. */ public E peek() { final ReentrantLock lock = this.lock; lock.lock(); try { return q.peek(); } finally { lock.unlock(); } } public int size() { final ReentrantLock lock = this.lock; lock.lock(); try { return q.size(); } 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; for (;;) { E first = q.peek(); if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) break; c.add(q.poll()); ++n; } if (n > 0) available.signalAll(); 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; while (n < maxElements) { E first = q.peek(); if (first == null || first.getDelay(TimeUnit.NANOSECONDS) > 0) break; c.add(q.poll()); ++n; } if (n > 0) available.signalAll(); return n; } finally { lock.unlock(); } } /** * Atomically removes all of the elements from this delay queue. * The queue will be empty after this call returns. * Elements with an unexpired delay are not waited for; they are * simply discarded from the queue. */ public void clear() { final ReentrantLock lock = this.lock; lock.lock(); try { q.clear(); } finally { lock.unlock(); } } /** * Always returns <tt>Integer.MAX_VALUE</tt> because * a <tt>DelayQueue</tt> is not capacity constrained. * * @return <tt>Integer.MAX_VALUE</tt> */ public int remainingCapacity() { return Integer.MAX_VALUE; } /** * 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(); } } /** * 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>The following code can be used to dump a delay queue into a newly * allocated array of <tt>Delayed</tt>: * * <pre> * Delayed[] a = q.toArray(new Delayed[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(); } } /** * Removes a single instance of the specified element from this * queue, if it is present, whether or not it has expired. */ public boolean remove(Object o) { final ReentrantLock lock = this.lock; lock.lock(); try { return q.remove(o); } finally { lock.unlock(); } } /** * Returns an iterator over all the elements (both expired and * unexpired) 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(); } } } }