- /*
- * @(#)BlockingQueue.java 1.8 04/07/12
- *
- * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
- * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- */
-
- package java.util.concurrent;
-
- import java.util.Collection;
- import java.util.Queue;
-
- /**
- * 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> <tt>BlockingQueue</tt> implementations are designed to be used
- * primarily for producer-consumer queues, but additionally support
- * 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.
- *
- * <p> <tt>BlockingQueue</tt> 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 <tt>addAll</tt>,
- * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
- * <em>not</em> necessarily performed atomically unless specified
- * otherwise in an implementation. So it is possible, for example, 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>
- *
- * <p>This interface is a member of the
- * <a href="{@docRoot}/../guide/collections/index.html">
- * Java Collections Framework</a>.
- *
- * @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 another thread is about to <tt>put</tt> or <tt>take</tt> an
- * element.
- * @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);
- }