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;
  
  /**
   * An object that executes submitted {@link Runnable} tasks. This
   * interface provides a way of decoupling task submission from the
   * mechanics of how each task will be run, including details of thread
   * use, scheduling, etc.  An {@code Executor} is normally used
   * instead of explicitly creating threads. For example, rather than
   * invoking {@code new Thread(new RunnableTask()).start()} for each
   * of a set of tasks, you might use:
   *
   * <pre> {@code
   * Executor executor = anExecutor();
   * executor.execute(new RunnableTask1());
   * executor.execute(new RunnableTask2());
   * ...}</pre>
   *
   * However, the {@code Executor} interface does not strictly require
   * that execution be asynchronous. In the simplest case, an executor
   * can run the submitted task immediately in the caller's thread:
   *
   * <pre> {@code
   * class DirectExecutor implements Executor {
   *   public void execute(Runnable r) {
   *     r.run();
   *   }
   * }}</pre>
   *
   * More typically, tasks are executed in some thread other than the
   * caller's thread.  The executor below spawns a new thread for each
   * task.
   *
   * <pre> {@code
   * class ThreadPerTaskExecutor implements Executor {
   *   public void execute(Runnable r) {
   *     new Thread(r).start();
   *   }
   * }}</pre>
   *
   * Many {@code Executor} implementations impose some sort of
   * limitation on how and when tasks are scheduled.  The executor below
   * serializes the submission of tasks to a second executor,
   * illustrating a composite executor.
   *
   * <pre> {@code
   * class SerialExecutor implements Executor {
   *   final Queue<Runnable> tasks = new ArrayDeque<>();
   *   final Executor executor;
   *   Runnable active;
   *
   *   SerialExecutor(Executor executor) {
   *     this.executor = executor;
   *   }
   *
   *   public synchronized void execute(final Runnable r) {
   *     tasks.add(new Runnable() {
   *       public void run() {
   *         try {
   *           r.run();
   *         } finally {
   *           scheduleNext();
   *         }
   *       }
   *     });
   *     if (active == null) {
   *       scheduleNext();
   *     }
   *   }
   *
   *   protected synchronized void scheduleNext() {
   *     if ((active = tasks.poll()) != null) {
   *       executor.execute(active);
   *     }
   *   }
   * }}</pre>
   *
   * The {@code Executor} implementations provided in this package
   * implement {@link ExecutorService}, which is a more extensive
   * interface.  The {@link ThreadPoolExecutor} class provides an
   * extensible thread pool implementation. The {@link Executors} class
   * provides convenient factory methods for these Executors.
   *
   * <p>Memory consistency effects: Actions in a thread prior to
   * submitting a {@code Runnable} object to an {@code Executor}
   * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
   * its execution begins, perhaps in another thread.
   *
   * @since 1.5
   * @author Doug Lea
   */
  public interface Executor {
  
      /**
       * Executes the given command at some time in the future.  The command
       * may execute in a new thread, in a pooled thread, or in the calling
       * thread, at the discretion of the {@code Executor} implementation.
       *
       * @param command the runnable task
       * @throws RejectedExecutionException if this task cannot be
       * accepted for execution
       * @throws NullPointerException if command is null
       */
      void execute(Runnable command);
  }
  