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	/*
	* 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 {@code Future} represents the result of an asynchronous
	* computation. Methods are provided to check if the computation is
	* complete, to wait for its completion, and to retrieve the result of
	* the computation. The result can only be retrieved using method
	* {@code get} when the computation has completed, blocking if
	* necessary until it is ready. Cancellation is performed by the
	* {@code cancel} method. Additional methods are provided to
	* determine if the task completed normally or was cancelled. Once a
	* computation has completed, the computation cannot be cancelled.
	* If you would like to use a {@code Future} for the sake
	* of cancellability but not provide a usable result, you can
	* declare types of the form {@code Future<?>} and
	* return {@code null} as a result of the underlying task.
	*
	* <p><b>Sample Usage</b> (Note that the following classes are all
	* made-up.)
	*
	* <pre> {@code
	* interface ArchiveSearcher { String search(String target); }
	* class App {
	* ExecutorService executor = ...;
	* ArchiveSearcher searcher = ...;
	* void showSearch(String target) throws InterruptedException {
	* Callable<String> task = () -> searcher.search(target);
	* Future<String> future = executor.submit(task);
	* displayOtherThings(); // do other things while searching
	* try {
	* displayText(future.get()); // use future
	* } catch (ExecutionException ex) { cleanup(); return; }
	* }
	* }}</pre>
	*
	* The {@link FutureTask} class is an implementation of {@code Future} that
	* implements {@code Runnable}, and so may be executed by an {@code Executor}.
	* For example, the above construction with {@code submit} could be replaced by:
	* <pre> {@code
	* FutureTask<String> future = new FutureTask<>(task);
	* executor.execute(future);}</pre>
	*
	* <p>Memory consistency effects: Actions taken by the asynchronous computation
	* <a href="package-summary.html#MemoryVisibility"> <i>happen-before</i></a>
	* actions following the corresponding {@code Future.get()} in another thread.
	*
	* @see FutureTask
	* @see Executor
	* @since 1.5
	* @author Doug Lea
	* @param <V> The result type returned by this Future's {@code get} method
	*/
	public interface Future<V> {

	/**
	* Attempts to cancel execution of this task. This method has no
	* effect if the task is already completed or cancelled, or could
	* not be cancelled for some other reason. Otherwise, if this
	* task has not started when {@code cancel} is called, this task
	* should never run. If the task has already started, then the
	* {@code mayInterruptIfRunning} parameter determines whether the
	* thread executing this task (when known by the implementation)
	* is interrupted in an attempt to stop the task.
	*
	* <p>The return value from this method does not necessarily
	* indicate whether the task is now cancelled; use {@link
	* #isCancelled}.
	*
	* @param mayInterruptIfRunning {@code true} if the thread
	* executing this task should be interrupted (if the thread is
	* known to the implementation); otherwise, in-progress tasks are
	* allowed to complete
	* @return {@code false} if the task could not be cancelled,
	* typically because it has already completed; {@code true}
	* otherwise. If two or more threads cause a task to be cancelled,
	* then at least one of them returns {@code true}. Implementations
	* may provide stronger guarantees.
	*/
	boolean cancel(boolean mayInterruptIfRunning);

	/**
	* Returns {@code true} if this task was cancelled before it completed
	* normally.
	*
	* @return {@code true} if this task was cancelled before it completed
	*/
	boolean isCancelled();

	/**
	* Returns {@code true} if this task completed.
	*
	* Completion may be due to normal termination, an exception, or
	* cancellation -- in all of these cases, this method will return
	* {@code true}.
	*
	* @return {@code true} if this task completed
	*/
	boolean isDone();

	/**
	* Waits if necessary for the computation to complete, and then
	* retrieves its result.
	*
	* @return the computed result
	* @throws CancellationException if the computation was cancelled
	* @throws ExecutionException if the computation threw an
	* exception
	* @throws InterruptedException if the current thread was interrupted
	* while waiting
	*/
	V get() throws InterruptedException, ExecutionException;

	/**
	* Waits if necessary for at most the given time for the computation
	* to complete, and then retrieves its result, if available.
	*
	* @param timeout the maximum time to wait
	* @param unit the time unit of the timeout argument
	* @return the computed result
	* @throws CancellationException if the computation was cancelled
	* @throws ExecutionException if the computation threw an
	* exception
	* @throws InterruptedException if the current thread was interrupted
	* while waiting
	* @throws TimeoutException if the wait timed out
	*/
	V get(long timeout, TimeUnit unit)
	throws InterruptedException, ExecutionException, TimeoutException;
	}

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