| /* |
| * 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. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.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/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.util.Collection; |
| import java.util.Queue; |
| |
| /** |
| * A {@link 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>{@code BlockingQueue} methods come in four forms, with different ways |
| * of handling operations that cannot be satisfied immediately, but may be |
| * satisfied at some point in the future: |
| * one throws an exception, the second returns a special value (either |
| * {@code null} or {@code false}, depending on the operation), the third |
| * blocks the current thread indefinitely until the operation can succeed, |
| * and the fourth blocks for only a given maximum time limit before giving |
| * up. These methods are summarized in the following table: |
| * |
| * <table class="plain"> |
| * <caption>Summary of BlockingQueue methods</caption> |
| * <tr> |
| * <td></td> |
| * <th scope="col" style="font-weight:normal; font-style:italic">Throws exception</th> |
| * <th scope="col" style="font-weight:normal; font-style:italic">Special value</th> |
| * <th scope="col" style="font-weight:normal; font-style:italic">Blocks</th> |
| * <th scope="col" style="font-weight:normal; font-style:italic">Times out</th> |
| * </tr> |
| * <tr> |
| * <th scope="row" style="text-align:left">Insert</th> |
| * <td>{@link #add(Object) add(e)}</td> |
| * <td>{@link #offer(Object) offer(e)}</td> |
| * <td>{@link #put(Object) put(e)}</td> |
| * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td> |
| * </tr> |
| * <tr> |
| * <th scope="row" style="text-align:left">Remove</th> |
| * <td>{@link #remove() remove()}</td> |
| * <td>{@link #poll() poll()}</td> |
| * <td>{@link #take() take()}</td> |
| * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td> |
| * </tr> |
| * <tr> |
| * <th scope="row" style="text-align:left">Examine</th> |
| * <td>{@link #element() element()}</td> |
| * <td>{@link #peek() peek()}</td> |
| * <td style="font-style: italic">not applicable</td> |
| * <td style="font-style: italic">not applicable</td> |
| * </tr> |
| * </table> |
| * |
| * <p>A {@code BlockingQueue} does not accept {@code null} elements. |
| * Implementations throw {@code NullPointerException} on attempts |
| * to {@code add}, {@code put} or {@code offer} a {@code null}. A |
| * {@code null} is used as a sentinel value to indicate failure of |
| * {@code poll} operations. |
| * |
| * <p>A {@code BlockingQueue} may be capacity bounded. At any given |
| * time it may have a {@code remainingCapacity} beyond which no |
| * additional elements can be {@code put} without blocking. |
| * A {@code BlockingQueue} without any intrinsic capacity constraints always |
| * reports a remaining capacity of {@code Integer.MAX_VALUE}. |
| * |
| * <p>{@code BlockingQueue} implementations are designed to be used |
| * primarily for producer-consumer queues, but additionally support |
| * the {@link Collection} interface. So, for example, it is |
| * possible to remove an arbitrary element from a queue using |
| * {@code remove(x)}. 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. |
| * |
| * <p>{@code BlockingQueue} implementations are thread-safe. All |
| * queuing methods achieve their effects atomically using internal |
| * locks or other forms of concurrency control. However, the |
| * <em>bulk</em> Collection operations {@code addAll}, |
| * {@code containsAll}, {@code retainAll} and {@code removeAll} are |
| * <em>not</em> necessarily performed atomically unless specified |
| * otherwise in an implementation. So it is possible, for example, for |
| * {@code addAll(c)} to fail (throwing an exception) after adding |
| * only some of the elements in {@code c}. |
| * |
| * <p>A {@code BlockingQueue} 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 {@code BlockingQueue} can safely be used with multiple |
| * producers and multiple consumers. |
| * <pre> {@code |
| * 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> |
| * |
| * <p>Memory consistency effects: As with other concurrent |
| * collections, actions in a thread prior to placing an object into a |
| * {@code BlockingQueue} |
| * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
| * actions subsequent to the access or removal of that element from |
| * the {@code BlockingQueue} in another thread. |
| * |
| * <p>This interface is a member of the |
| * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework"> |
| * Java Collections Framework</a>. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <E> the type of elements held in this queue |
| */ |
| public interface BlockingQueue<E> extends Queue<E> { |
| /** |
| * Inserts the specified element into this queue if it is possible to do |
| * so immediately without violating capacity restrictions, returning |
| * {@code true} upon success and throwing an |
| * {@code IllegalStateException} if no space is currently available. |
| * When using a capacity-restricted queue, it is generally preferable to |
| * use {@link #offer(Object) offer}. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Collection#add}) |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this queue |
| * @throws NullPointerException if the specified element is null |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this queue |
| */ |
| boolean add(E e); |
| |
| /** |
| * Inserts the specified element into this queue if it is possible to do |
| * so immediately without violating capacity restrictions, returning |
| * {@code true} upon success and {@code false} if no space is currently |
| * available. When using a capacity-restricted queue, this method is |
| * generally preferable to {@link #add}, which can fail to insert an |
| * element only by throwing an exception. |
| * |
| * @param e the element to add |
| * @return {@code true} if the element was added to this queue, else |
| * {@code false} |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this queue |
| * @throws NullPointerException if the specified element is null |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this queue |
| */ |
| boolean offer(E e); |
| |
| /** |
| * Inserts the specified element into this queue, waiting if necessary |
| * for space to become available. |
| * |
| * @param e the element to add |
| * @throws InterruptedException if interrupted while waiting |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this queue |
| * @throws NullPointerException if the specified element is null |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this queue |
| */ |
| void put(E e) throws InterruptedException; |
| |
| /** |
| * Inserts the specified element into this queue, waiting up to the |
| * specified wait time if necessary for space to become available. |
| * |
| * @param e the element to add |
| * @param timeout how long to wait before giving up, in units of |
| * {@code unit} |
| * @param unit a {@code TimeUnit} determining how to interpret the |
| * {@code timeout} parameter |
| * @return {@code true} if successful, or {@code false} if |
| * the specified waiting time elapses before space is available |
| * @throws InterruptedException if interrupted while waiting |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this queue |
| * @throws NullPointerException if the specified element is null |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this queue |
| */ |
| boolean offer(E e, long timeout, TimeUnit unit) |
| throws InterruptedException; |
| |
| /** |
| * Retrieves and removes the head of this queue, waiting if necessary |
| * until an element becomes available. |
| * |
| * @return the head of this queue |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| E take() throws InterruptedException; |
| |
| /** |
| * Retrieves and removes the head of this queue, waiting up to the |
| * specified wait time if necessary for an element to become available. |
| * |
| * @param timeout how long to wait before giving up, in units of |
| * {@code unit} |
| * @param unit a {@code TimeUnit} determining how to interpret the |
| * {@code timeout} parameter |
| * @return the head of this queue, or {@code null} if the |
| * specified waiting time elapses before an element is available |
| * @throws InterruptedException if interrupted while waiting |
| */ |
| E poll(long timeout, TimeUnit unit) |
| throws InterruptedException; |
| |
| /** |
| * Returns the number of additional elements that this queue can ideally |
| * (in the absence of memory or resource constraints) accept without |
| * blocking, or {@code Integer.MAX_VALUE} if there is no intrinsic |
| * limit. |
| * |
| * <p>Note that you <em>cannot</em> always tell if an attempt to insert |
| * an element will succeed by inspecting {@code remainingCapacity} |
| * because it may be the case that another thread is about to |
| * insert or remove an element. |
| * |
| * @return the remaining capacity |
| */ |
| int remainingCapacity(); |
| |
| /** |
| * 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 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 {@code true} if this queue changed as a result of the call |
| * @throws ClassCastException if the class of the specified element |
| * is incompatible with this queue |
| * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null |
| * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean remove(Object o); |
| |
| /** |
| * 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 {@code true} if this queue contains the specified element |
| * @throws ClassCastException if the class of the specified element |
| * is incompatible with this queue |
| * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null |
| * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean contains(Object o); |
| |
| /** |
| * Removes all available elements from this queue and adds them |
| * to the given collection. This operation may be more |
| * efficient than repeatedly polling this queue. A failure |
| * encountered while attempting to add elements to |
| * collection {@code c} 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 |
| * {@code IllegalArgumentException}. 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 UnsupportedOperationException if addition of elements |
| * is not supported by the specified collection |
| * @throws ClassCastException if the class of an element of this queue |
| * prevents it from being added to the specified collection |
| * @throws NullPointerException if the specified collection is null |
| * @throws IllegalArgumentException if the specified collection is this |
| * queue, or some property of an element of this queue prevents |
| * it from being added to the specified collection |
| */ |
| int drainTo(Collection<? super E> c); |
| |
| /** |
| * Removes at most the given number of available elements from |
| * this queue and adds them to the given collection. A failure |
| * encountered while attempting to add elements to |
| * collection {@code c} 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 |
| * {@code IllegalArgumentException}. 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 UnsupportedOperationException if addition of elements |
| * is not supported by the specified collection |
| * @throws ClassCastException if the class of an element of this queue |
| * prevents it from being added to the specified collection |
| * @throws NullPointerException if the specified collection is null |
| * @throws IllegalArgumentException if the specified collection is this |
| * queue, or some property of an element of this queue prevents |
| * it from being added to the specified collection |
| */ |
| int drainTo(Collection<? super E> c, int maxElements); |
| } |