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;
  
  /**
   * A service that decouples the production of new asynchronous tasks
   * from the consumption of the results of completed tasks.  Producers
   * {@code submit} tasks for execution. Consumers {@code take}
   * completed tasks and process their results in the order they
   * complete.  A {@code CompletionService} can for example be used to
   * manage asynchronous I/O, in which tasks that perform reads are
   * submitted in one part of a program or system, and then acted upon
   * in a different part of the program when the reads complete,
   * possibly in a different order than they were requested.
   *
   * <p>Typically, a {@code CompletionService} relies on a separate
   * {@link Executor} to actually execute the tasks, in which case the
   * {@code CompletionService} only manages an internal completion
   * queue. The {@link ExecutorCompletionService} class provides an
   * implementation of this approach.
   *
   * <p>Memory consistency effects: Actions in a thread prior to
   * submitting a task to a {@code CompletionService}
   * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
   * actions taken by that task, which in turn <i>happen-before</i>
   * actions following a successful return from the corresponding {@code take()}.
   */
  public interface CompletionService<V> {
      /**
       * Submits a value-returning task for execution and returns a Future
       * representing the pending results of the task.  Upon completion,
       * this task may be taken or polled.
       *
       * @param task the task to submit
       * @return a Future representing pending completion of the task
       * @throws RejectedExecutionException if the task cannot be
       *         scheduled for execution
       * @throws NullPointerException if the task is null
       */
      Future<V> submit(Callable<V> task);
  
      /**
       * Submits a Runnable task for execution and returns a Future
       * representing that task.  Upon completion, this task may be
       * taken or polled.
       *
       * @param task the task to submit
       * @param result the result to return upon successful completion
       * @return a Future representing pending completion of the task,
       *         and whose {@code get()} method will return the given
       *         result value upon completion
       * @throws RejectedExecutionException if the task cannot be
       *         scheduled for execution
       * @throws NullPointerException if the task is null
       */
      Future<V> submit(Runnable task, V result);
  
      /**
       * Retrieves and removes the Future representing the next
       * completed task, waiting if none are yet present.
       *
       * @return the Future representing the next completed task
       * @throws InterruptedException if interrupted while waiting
       */
      Future<V> take() throws InterruptedException;
  
      /**
       * Retrieves and removes the Future representing the next
       * completed task, or {@code null} if none are present.
       *
       * @return the Future representing the next completed task, or
       *         {@code null} if none are present
       */
      Future<V> poll();
  
      /**
       * Retrieves and removes the Future representing the next
       * completed task, waiting if necessary up to the specified wait
       * time if none are yet present.
       *
       * @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 Future representing the next completed task or
       *         {@code null} if the specified waiting time elapses
       *         before one is present
       * @throws InterruptedException if interrupted while waiting
       */
      Future<V> poll(long timeout, TimeUnit unit) throws InterruptedException;
  }
  