--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/ArrayBlockingQueue.java Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,807 @@
+/*
+ * 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. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.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.*;
+
+/**
+ * A bounded {@linkplain BlockingQueue blocking queue} backed by an
+ * array. This queue orders elements FIFO (first-in-first-out). The
+ * <em>head</em> of the queue is that element that has been on the
+ * queue the longest time. The <em>tail</em> of the queue is that
+ * element that has been on the queue the shortest time. New elements
+ * are inserted at the tail of the queue, and the queue retrieval
+ * operations obtain elements at the head of the queue.
+ *
+ * <p>This is a classic "bounded buffer", in which a
+ * fixed-sized array holds elements inserted by producers and
+ * extracted by consumers. Once created, the capacity cannot be
+ * increased. Attempts to <tt>put</tt> an element into a full queue
+ * will result in the operation blocking; attempts to <tt>take</tt> an
+ * element from an empty queue will similarly block.
+ *
+ * <p> This class supports an optional fairness policy for ordering
+ * waiting producer and consumer threads. By default, this ordering
+ * is not guaranteed. However, a queue constructed with fairness set
+ * to <tt>true</tt> grants threads access in FIFO order. Fairness
+ * generally decreases throughput but reduces variability and avoids
+ * starvation.
+ *
+ * <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 ArrayBlockingQueue<E> extends AbstractQueue<E>
+ implements BlockingQueue<E>, java.io.Serializable {
+
+ /**
+ * Serialization ID. This class relies on default serialization
+ * even for the items array, which is default-serialized, even if
+ * it is empty. Otherwise it could not be declared final, which is
+ * necessary here.
+ */
+ private static final long serialVersionUID = -817911632652898426L;
+
+ /** The queued items */
+ private final E[] items;
+ /** items index for next take, poll or remove */
+ private int takeIndex;
+ /** items index for next put, offer, or add. */
+ private int putIndex;
+ /** Number of items in the queue */
+ private int count;
+
+ /*
+ * Concurrency control uses the classic two-condition algorithm
+ * found in any textbook.
+ */
+
+ /** Main lock guarding all access */
+ private final ReentrantLock lock;
+ /** Condition for waiting takes */
+ private final Condition notEmpty;
+ /** Condition for waiting puts */
+ private final Condition notFull;
+
+ // Internal helper methods
+
+ /**
+ * Circularly increment i.
+ */
+ final int inc(int i) {
+ return (++i == items.length)? 0 : i;
+ }
+
+ /**
+ * Inserts element at current put position, advances, and signals.
+ * Call only when holding lock.
+ */
+ private void insert(E x) {
+ items[putIndex] = x;
+ putIndex = inc(putIndex);
+ ++count;
+ notEmpty.signal();
+ }
+
+ /**
+ * Extracts element at current take position, advances, and signals.
+ * Call only when holding lock.
+ */
+ private E extract() {
+ final E[] items = this.items;
+ E x = items[takeIndex];
+ items[takeIndex] = null;
+ takeIndex = inc(takeIndex);
+ --count;
+ notFull.signal();
+ return x;
+ }
+
+ /**
+ * Utility for remove and iterator.remove: Delete item at position i.
+ * Call only when holding lock.
+ */
+ void removeAt(int i) {
+ final E[] items = this.items;
+ // if removing front item, just advance
+ if (i == takeIndex) {
+ items[takeIndex] = null;
+ takeIndex = inc(takeIndex);
+ } else {
+ // slide over all others up through putIndex.
+ for (;;) {
+ int nexti = inc(i);
+ if (nexti != putIndex) {
+ items[i] = items[nexti];
+ i = nexti;
+ } else {
+ items[i] = null;
+ putIndex = i;
+ break;
+ }
+ }
+ }
+ --count;
+ notFull.signal();
+ }
+
+ /**
+ * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
+ * capacity and default access policy.
+ *
+ * @param capacity the capacity of this queue
+ * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
+ */
+ public ArrayBlockingQueue(int capacity) {
+ this(capacity, false);
+ }
+
+ /**
+ * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
+ * capacity and the specified access policy.
+ *
+ * @param capacity the capacity of this queue
+ * @param fair if <tt>true</tt> then queue accesses for threads blocked
+ * on insertion or removal, are processed in FIFO order;
+ * if <tt>false</tt> the access order is unspecified.
+ * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
+ */
+ public ArrayBlockingQueue(int capacity, boolean fair) {
+ if (capacity <= 0)
+ throw new IllegalArgumentException();
+ this.items = (E[]) new Object[capacity];
+ lock = new ReentrantLock(fair);
+ notEmpty = lock.newCondition();
+ notFull = lock.newCondition();
+ }
+
+ /**
+ * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
+ * capacity, the specified access policy and initially containing the
+ * elements of the given collection,
+ * added in traversal order of the collection's iterator.
+ *
+ * @param capacity the capacity of this queue
+ * @param fair if <tt>true</tt> then queue accesses for threads blocked
+ * on insertion or removal, are processed in FIFO order;
+ * if <tt>false</tt> the access order is unspecified.
+ * @param c the collection of elements to initially contain
+ * @throws IllegalArgumentException if <tt>capacity</tt> is less than
+ * <tt>c.size()</tt>, or less than 1.
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ public ArrayBlockingQueue(int capacity, boolean fair,
+ Collection<? extends E> c) {
+ this(capacity, fair);
+ if (capacity < c.size())
+ throw new IllegalArgumentException();
+
+ for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
+ add(it.next());
+ }
+
+ /**
+ * Inserts the specified element at the tail of this queue if it is
+ * possible to do so immediately without exceeding the queue's capacity,
+ * returning <tt>true</tt> upon success and throwing an
+ * <tt>IllegalStateException</tt> if this queue is full.
+ *
+ * @param e the element to add
+ * @return <tt>true</tt> (as specified by {@link Collection#add})
+ * @throws IllegalStateException if this queue is full
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean add(E e) {
+ return super.add(e);
+ }
+
+ /**
+ * Inserts the specified element at the tail of this queue if it is
+ * possible to do so immediately without exceeding the queue's capacity,
+ * returning <tt>true</tt> upon success and <tt>false</tt> if this queue
+ * is full. This method is generally preferable to method {@link #add},
+ * which can fail to insert an element only by throwing an exception.
+ *
+ * @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();
+ try {
+ if (count == items.length)
+ return false;
+ else {
+ insert(e);
+ return true;
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Inserts the specified element at the tail of this queue, waiting
+ * for space to become available if the queue is full.
+ *
+ * @throws InterruptedException {@inheritDoc}
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public void put(E e) throws InterruptedException {
+ if (e == null) throw new NullPointerException();
+ final E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lockInterruptibly();
+ try {
+ try {
+ while (count == items.length)
+ notFull.await();
+ } catch (InterruptedException ie) {
+ notFull.signal(); // propagate to non-interrupted thread
+ throw ie;
+ }
+ insert(e);
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Inserts the specified element at the tail of this queue, waiting
+ * up to the specified wait time for space to become available if
+ * the queue is full.
+ *
+ * @throws InterruptedException {@inheritDoc}
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean offer(E e, long timeout, TimeUnit unit)
+ throws InterruptedException {
+
+ if (e == null) throw new NullPointerException();
+ long nanos = unit.toNanos(timeout);
+ final ReentrantLock lock = this.lock;
+ lock.lockInterruptibly();
+ try {
+ for (;;) {
+ if (count != items.length) {
+ insert(e);
+ return true;
+ }
+ if (nanos <= 0)
+ return false;
+ try {
+ nanos = notFull.awaitNanos(nanos);
+ } catch (InterruptedException ie) {
+ notFull.signal(); // propagate to non-interrupted thread
+ throw ie;
+ }
+ }
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ public E poll() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ if (count == 0)
+ return null;
+ E x = extract();
+ return x;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ public E take() throws InterruptedException {
+ final ReentrantLock lock = this.lock;
+ lock.lockInterruptibly();
+ try {
+ try {
+ while (count == 0)
+ notEmpty.await();
+ } catch (InterruptedException ie) {
+ notEmpty.signal(); // propagate to non-interrupted thread
+ throw ie;
+ }
+ E x = extract();
+ 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 (;;) {
+ if (count != 0) {
+ E x = extract();
+ 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 (count == 0) ? null : items[takeIndex];
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ // this doc comment is overridden to remove the reference to collections
+ // greater in size than Integer.MAX_VALUE
+ /**
+ * Returns the number of elements in this queue.
+ *
+ * @return the number of elements in this queue
+ */
+ public int size() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ return count;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ // this doc comment is a modified copy of the inherited doc comment,
+ // without the reference to unlimited queues.
+ /**
+ * Returns the number of additional elements that this queue can ideally
+ * (in the absence of memory or resource constraints) accept without
+ * blocking. This is always equal to the initial capacity of this queue
+ * less the current <tt>size</tt> of this queue.
+ *
+ * <p>Note that you <em>cannot</em> always tell if an attempt to insert
+ * an element will succeed by inspecting <tt>remainingCapacity</tt>
+ * because it may be the case that another thread is about to
+ * insert or remove an element.
+ */
+ public int remainingCapacity() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ return items.length - count;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Removes a single instance of the specified element from this queue,
+ * if it is present. More formally, removes an element <tt>e</tt> such
+ * that <tt>o.equals(e)</tt>, if this queue contains one or more such
+ * elements.
+ * Returns <tt>true</tt> 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) {
+ if (o == null) return false;
+ final E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int i = takeIndex;
+ int k = 0;
+ for (;;) {
+ if (k++ >= count)
+ return false;
+ if (o.equals(items[i])) {
+ removeAt(i);
+ return true;
+ }
+ i = inc(i);
+ }
+
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Returns <tt>true</tt> if this queue contains the specified element.
+ * More formally, returns <tt>true</tt> if and only if this queue contains
+ * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
+ *
+ * @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) {
+ if (o == null) return false;
+ final E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int i = takeIndex;
+ int k = 0;
+ while (k++ < count) {
+ if (o.equals(items[i]))
+ return true;
+ i = inc(i);
+ }
+ return false;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Returns an array containing all of the elements in this queue, in
+ * proper sequence.
+ *
+ * <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 E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ Object[] a = new Object[count];
+ int k = 0;
+ int i = takeIndex;
+ while (k < count) {
+ a[k++] = items[i];
+ i = inc(i);
+ }
+ return a;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Returns an array containing all of the elements in this queue, in
+ * proper sequence; the runtime type of the returned array is that of
+ * the specified array. 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 E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ if (a.length < count)
+ a = (T[])java.lang.reflect.Array.newInstance(
+ a.getClass().getComponentType(),
+ count
+ );
+
+ int k = 0;
+ int i = takeIndex;
+ while (k < count) {
+ a[k++] = (T)items[i];
+ i = inc(i);
+ }
+ if (a.length > count)
+ a[count] = null;
+ return a;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ public String toString() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ return super.toString();
+ } 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 E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int i = takeIndex;
+ int k = count;
+ while (k-- > 0) {
+ items[i] = null;
+ i = inc(i);
+ }
+ count = 0;
+ putIndex = 0;
+ takeIndex = 0;
+ notFull.signalAll();
+ } 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 E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int i = takeIndex;
+ int n = 0;
+ int max = count;
+ while (n < max) {
+ c.add(items[i]);
+ items[i] = null;
+ i = inc(i);
+ ++n;
+ }
+ if (n > 0) {
+ count = 0;
+ putIndex = 0;
+ takeIndex = 0;
+ notFull.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 E[] items = this.items;
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ int i = takeIndex;
+ int n = 0;
+ int sz = count;
+ int max = (maxElements < count)? maxElements : count;
+ while (n < max) {
+ c.add(items[i]);
+ items[i] = null;
+ i = inc(i);
+ ++n;
+ }
+ if (n > 0) {
+ count -= n;
+ takeIndex = i;
+ notFull.signalAll();
+ }
+ return n;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+
+ /**
+ * Returns an iterator over the elements in this queue in proper sequence.
+ * 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 in proper sequence
+ */
+ public Iterator<E> iterator() {
+ final ReentrantLock lock = this.lock;
+ lock.lock();
+ try {
+ return new Itr();
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * Iterator for ArrayBlockingQueue
+ */
+ private class Itr implements Iterator<E> {
+ /**
+ * Index of element to be returned by next,
+ * or a negative number if no such.
+ */
+ private int nextIndex;
+
+ /**
+ * nextItem holds on to item fields because once we claim
+ * that an element exists in hasNext(), we must return it in
+ * the following next() call even if it was in the process of
+ * being removed when hasNext() was called.
+ */
+ private E nextItem;
+
+ /**
+ * Index of element returned by most recent call to next.
+ * Reset to -1 if this element is deleted by a call to remove.
+ */
+ private int lastRet;
+
+ Itr() {
+ lastRet = -1;
+ if (count == 0)
+ nextIndex = -1;
+ else {
+ nextIndex = takeIndex;
+ nextItem = items[takeIndex];
+ }
+ }
+
+ public boolean hasNext() {
+ /*
+ * No sync. We can return true by mistake here
+ * only if this iterator passed across threads,
+ * which we don't support anyway.
+ */
+ return nextIndex >= 0;
+ }
+
+ /**
+ * Checks whether nextIndex is valid; if so setting nextItem.
+ * Stops iterator when either hits putIndex or sees null item.
+ */
+ private void checkNext() {
+ if (nextIndex == putIndex) {
+ nextIndex = -1;
+ nextItem = null;
+ } else {
+ nextItem = items[nextIndex];
+ if (nextItem == null)
+ nextIndex = -1;
+ }
+ }
+
+ public E next() {
+ final ReentrantLock lock = ArrayBlockingQueue.this.lock;
+ lock.lock();
+ try {
+ if (nextIndex < 0)
+ throw new NoSuchElementException();
+ lastRet = nextIndex;
+ E x = nextItem;
+ nextIndex = inc(nextIndex);
+ checkNext();
+ return x;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ public void remove() {
+ final ReentrantLock lock = ArrayBlockingQueue.this.lock;
+ lock.lock();
+ try {
+ int i = lastRet;
+ if (i == -1)
+ throw new IllegalStateException();
+ lastRet = -1;
+
+ int ti = takeIndex;
+ removeAt(i);
+ // back up cursor (reset to front if was first element)
+ nextIndex = (i == ti) ? takeIndex : i;
+ checkNext();
+ } finally {
+ lock.unlock();
+ }
+ }
+ }
+}