| /* |
| * 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.Collection; |
| import java.util.Queue; |
| |
| // BEGIN android-note |
| // removed link to collections framework docs |
| // END android-note |
| |
| /** |
| * A {@link java.util.Queue} that additionally supports operations |
| * that wait for the queue to become non-empty when retrieving an element, |
| * and wait for space to become available in the queue when storing an |
| * element. |
| * |
| * <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements. |
| * Implementations throw <tt>NullPointerException</tt> on attempts |
| * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A |
| * <tt>null</tt> is used as a sentinel value to indicate failure of |
| * <tt>poll</tt> operations. |
| * |
| * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given |
| * time it may have a <tt>remainingCapacity</tt> beyond which no |
| * additional elements can be <tt>put</tt> without blocking. |
| * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always |
| * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>. |
| * |
| * <p> While <tt>BlockingQueue</tt> is designed to be used primarily |
| * for producer-consumer queues, it additionally supports the {@link |
| * java.util.Collection} interface. So, for example, it is possible |
| * to remove an arbitrary element from a queue using |
| * <tt>remove(x)</tt>. However, such operations are in general |
| * <em>not</em> performed very efficiently, and are intended for only |
| * occasional use, such as when a queued message is cancelled. Also, |
| * the bulk Collection operations, most notably <tt>addAll</tt>, are |
| * <em>not</em> necessarily performed atomically, so it is possible |
| * for <tt>addAll(c)</tt> to fail (throwing an exception) after adding |
| * only some of the elements in <tt>c</tt>. |
| * |
| * <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support |
| * any kind of "close" or "shutdown" operation to |
| * indicate that no more items will be added. The needs and usage of |
| * such features tend to be implementation-dependent. For example, a |
| * common tactic is for producers to insert special |
| * <em>end-of-stream</em> or <em>poison</em> objects, that are |
| * interpreted accordingly when taken by consumers. |
| * |
| * <p> |
| * Usage example, based on a typical producer-consumer scenario. |
| * Note that a <tt>BlockingQueue</tt> can safely be used with multiple |
| * producers and multiple consumers. |
| * <pre> |
| * class Producer implements Runnable { |
| * private final BlockingQueue queue; |
| * Producer(BlockingQueue q) { queue = q; } |
| * public void run() { |
| * try { |
| * while(true) { queue.put(produce()); } |
| * } catch (InterruptedException ex) { ... handle ...} |
| * } |
| * Object produce() { ... } |
| * } |
| * |
| * class Consumer implements Runnable { |
| * private final BlockingQueue queue; |
| * Consumer(BlockingQueue q) { queue = q; } |
| * public void run() { |
| * try { |
| * while(true) { consume(queue.take()); } |
| * } catch (InterruptedException ex) { ... handle ...} |
| * } |
| * void consume(Object x) { ... } |
| * } |
| * |
| * class Setup { |
| * void main() { |
| * BlockingQueue q = new SomeQueueImplementation(); |
| * Producer p = new Producer(q); |
| * Consumer c1 = new Consumer(q); |
| * Consumer c2 = new Consumer(q); |
| * new Thread(p).start(); |
| * new Thread(c1).start(); |
| * new Thread(c2).start(); |
| * } |
| * } |
| * </pre> |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <E> the type of elements held in this collection |
| */ |
| public interface BlockingQueue<E> extends Queue<E> { |
| |
| /** |
| * Inserts the specified element into this queue, if possible. When |
| * using queues that may impose insertion restrictions (for |
| * example capacity bounds), method <tt>offer</tt> is generally |
| * preferable to method {@link Collection#add}, which can fail to |
| * insert an element only by throwing an exception. |
| * |
| * @param o the element to add. |
| * @return <tt>true</tt> if it was possible to add the element to |
| * this queue, else <tt>false</tt> |
| * @throws NullPointerException if the specified element is <tt>null</tt> |
| */ |
| boolean offer(E o); |
| |
| /** |
| * Inserts the specified element into this queue, waiting if necessary |
| * up to the specified wait time for space to become available. |
| * @param o the element to add |
| * @param timeout how long to wait before giving up, in units of |
| * <tt>unit</tt> |
| * @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| * <tt>timeout</tt> parameter |
| * @return <tt>true</tt> if successful, or <tt>false</tt> if |
| * the specified waiting time elapses before space is available. |
| * @throws InterruptedException if interrupted while waiting. |
| * @throws NullPointerException if the specified element is <tt>null</tt>. |
| */ |
| boolean offer(E o, long timeout, TimeUnit unit) |
| throws InterruptedException; |
| |
| /** |
| * Retrieves and removes the head of this queue, waiting |
| * if necessary up to the specified wait time if no elements are |
| * present on this queue. |
| * @param timeout how long to wait before giving up, in units of |
| * <tt>unit</tt> |
| * @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| * <tt>timeout</tt> parameter |
| * @return the head of this queue, or <tt>null</tt> if the |
| * specified waiting time elapses before an element is present. |
| * @throws InterruptedException if interrupted while waiting. |
| */ |
| E poll(long timeout, TimeUnit unit) |
| throws InterruptedException; |
| |
| /** |
| * Retrieves and removes the head of this queue, waiting |
| * if no elements are present on this queue. |
| * @return the head of this queue |
| * @throws InterruptedException if interrupted while waiting. |
| */ |
| E take() throws InterruptedException; |
| |
| /** |
| * Adds the specified element to this queue, waiting if necessary for |
| * space to become available. |
| * @param o the element to add |
| * @throws InterruptedException if interrupted while waiting. |
| * @throws NullPointerException if the specified element is <tt>null</tt>. |
| */ |
| void put(E o) throws InterruptedException; |
| |
| /** |
| * Returns the number of elements that this queue can ideally (in |
| * the absence of memory or resource constraints) accept without |
| * blocking, or <tt>Integer.MAX_VALUE</tt> if there is no |
| * intrinsic limit. |
| * <p>Note that you <em>cannot</em> always tell if |
| * an attempt to <tt>add</tt> an element will succeed by |
| * inspecting <tt>remainingCapacity</tt> because it may be the |
| * case that a waiting consumer is ready to <tt>take</tt> an |
| * element out of an otherwise full queue. |
| * @return the remaining capacity |
| */ |
| int remainingCapacity(); |
| |
| /** |
| * Adds the specified element to this queue if it is possible to |
| * do so immediately, returning <tt>true</tt> upon success, else |
| * throwing an IllegalStateException. |
| * @param o the element |
| * @return <tt>true</tt> (as per the general contract of |
| * <tt>Collection.add</tt>). |
| * |
| * @throws NullPointerException if the specified element is <tt>null</tt> |
| * @throws IllegalStateException if element cannot be added |
| */ |
| boolean add(E o); |
| |
| /** |
| * Removes all available elements from this queue and adds them |
| * into the given collection. This operation may be more |
| * efficient than repeatedly polling this queue. A failure |
| * encountered while attempting to <tt>add</tt> elements to |
| * collection <tt>c</tt> may result in elements being in neither, |
| * either or both collections when the associated exception is |
| * thrown. Attempts to drain a queue to itself result in |
| * <tt>IllegalArgumentException</tt>. Further, the behavior of |
| * this operation is undefined if the specified collection is |
| * modified while the operation is in progress. |
| * |
| * @param c the collection to transfer elements into |
| * @return the number of elements transferred. |
| * @throws NullPointerException if c is null |
| * @throws IllegalArgumentException if c is this queue |
| * |
| */ |
| int drainTo(Collection<? super E> c); |
| |
| /** |
| * Removes at most the given number of available elements from |
| * this queue and adds them into the given collection. A failure |
| * encountered while attempting to <tt>add</tt> elements to |
| * collection <tt>c</tt> may result in elements being in neither, |
| * either or both collections when the associated exception is |
| * thrown. Attempts to drain a queue to itself result in |
| * <tt>IllegalArgumentException</tt>. Further, the behavior of |
| * this operation is undefined if the specified collection is |
| * modified while the operation is in progress. |
| * |
| * @param c the collection to transfer elements into |
| * @param maxElements the maximum number of elements to transfer |
| * @return the number of elements transferred. |
| * @throws NullPointerException if c is null |
| * @throws IllegalArgumentException if c is this queue |
| */ |
| int drainTo(Collection<? super E> c, int maxElements); |
| } |
