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Diffstat (limited to 'external/jsr166/java/util/concurrent/ArrayBlockingQueue.java')
| -rw-r--r-- | external/jsr166/java/util/concurrent/ArrayBlockingQueue.java | 778 |
1 files changed, 778 insertions, 0 deletions
diff --git a/external/jsr166/java/util/concurrent/ArrayBlockingQueue.java b/external/jsr166/java/util/concurrent/ArrayBlockingQueue.java new file mode 100644 index 000000000..bdf34d28a --- /dev/null +++ b/external/jsr166/java/util/concurrent/ArrayBlockingQueue.java @@ -0,0 +1,778 @@ +/* + * 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(); + } + } + } +} |