content: /*
   * 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;
  
  // BEGIN android-note
  // removed link to collections framework docs
  // END android-note
  
  /**
   * A {@link BlockingQueue} in which producers may wait for consumers
   * to receive elements.  A {@code TransferQueue} may be useful for
   * example in message passing applications in which producers
   * sometimes (using method {@link #transfer}) await receipt of
   * elements by consumers invoking {@code take} or {@code poll}, while
   * at other times enqueue elements (via method {@code put}) without
   * waiting for receipt.
   * {@linkplain #tryTransfer(Object) Non-blocking} and
   * {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
   * {@code tryTransfer} are also available.
   * A {@code TransferQueue} may also be queried, via {@link
   * #hasWaitingConsumer}, whether there are any threads waiting for
   * items, which is a converse analogy to a {@code peek} operation.
   *
   * <p>Like other blocking queues, a {@code TransferQueue} may be
   * capacity bounded.  If so, an attempted transfer operation may
   * initially block waiting for available space, and/or subsequently
   * block waiting for reception by a consumer.  Note that in a queue
   * with zero capacity, such as {@link SynchronousQueue}, {@code put}
   * and {@code transfer} are effectively synonymous.
   *
   * @since 1.7
   * @author Doug Lea
   * @param <E> the type of elements held in this queue
   */
  public interface TransferQueue<E> extends BlockingQueue<E> {
      /**
       * Transfers the element to a waiting consumer immediately, if possible.
       *
       * <p>More precisely, transfers the specified element immediately
       * if there exists a consumer already waiting to receive it (in
       * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
       * otherwise returning {@code false} without enqueuing the element.
       *
       * @param e the element to transfer
       * @return {@code true} if the element was transferred, 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 tryTransfer(E e);
  
      /**
       * Transfers the element to a consumer, waiting if necessary to do so.
       *
       * <p>More precisely, transfers the specified element immediately
       * if there exists a consumer already waiting to receive it (in
       * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
       * else waits until the element is received by a consumer.
       *
       * @param e the element to transfer
       * @throws InterruptedException if interrupted while waiting,
       *         in which case the element is not left enqueued
       * @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 transfer(E e) throws InterruptedException;
  
      /**
       * Transfers the element to a consumer if it is possible to do so
       * before the timeout elapses.
       *
       * <p>More precisely, transfers the specified element immediately
       * if there exists a consumer already waiting to receive it (in
       * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
       * else waits until the element is received by a consumer,
       * returning {@code false} if the specified wait time elapses
       * before the element can be transferred.
       *
       * @param e the element to transfer
       * @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 completion,
       *         in which case the element is not left enqueued
       * @throws InterruptedException if interrupted while waiting,
       *         in which case the element is not left enqueued
       * @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 tryTransfer(E e, long timeout, TimeUnit unit)
          throws InterruptedException;
  
      /**
       * Returns {@code true} if there is at least one consumer waiting
       * to receive an element via {@link #take} or
       * timed {@link #poll(long,TimeUnit) poll}.
       * The return value represents a momentary state of affairs.
       *
       * @return {@code true} if there is at least one waiting consumer
       */
      boolean hasWaitingConsumer();
  
      /**
       * Returns an estimate of the number of consumers waiting to
       * receive elements via {@link #take} or timed
       * {@link #poll(long,TimeUnit) poll}.  The return value is an
       * approximation of a momentary state of affairs, that may be
       * inaccurate if consumers have completed or given up waiting.
       * The value may be useful for monitoring and heuristics, but
       * not for synchronization control.  Implementations of this
       * method are likely to be noticeably slower than those for
       * {@link #hasWaitingConsumer}.
       *
       * @return the number of consumers waiting to receive elements
       */
      int getWaitingConsumerCount();
  }
  