content: /*
   *  Copyright Beijing 58 Information Technology Co.,Ltd.
   *
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
   *  with the License.  You may obtain a copy of the License at
   *
   *        http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License.
   */
  /*
   * 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/licenses/publicdomain
   */
  
  package com.bj58.spat.gaea.server.util.jsr166;
  import java.util.concurrent.*;
  
  /**
   * 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.
   *
   * <p>This interface is a member of the
   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   * Java Collections Framework</a>.
   *
   * @since 1.7
   * @author Doug Lea
   * @param <E> the type of elements held in this collection
   */
  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();
  }