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	/*
	* 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.base/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.base/java/util/Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null
	* (<a href="{@docRoot}/java.base/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.base/java/util/Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null
	* (<a href="{@docRoot}/java.base/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);
	}

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