/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

/*
 *
 *
 *
 *
 *
 * 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 &quot;close&quot; or &quot;shutdown&quot; 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);
}