/*
* 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/licenses/publicdomain
*/
package java.util.concurrent;
/**
* A <tt>Future</tt> 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
* <tt>get</tt> when the computation has completed, blocking if
* necessary until it is ready. Cancellation is performed by the
* <tt>cancel</tt> 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 <tt>Future</tt> for the sake
* of cancellability but not provide a usable result, you can
* declare types of the form <tt>Future<?></tt> and
* return <tt>null</tt> as a result of the underlying task.
*
* <p>
* <b>Sample Usage</b> (Note that the following classes are all
* made-up.) <p>
* <pre>
* interface ArchiveSearcher { String search(String target); }
* class App {
* ExecutorService executor = ...
* ArchiveSearcher searcher = ...
* void showSearch(final String target)
* throws InterruptedException {
* Future<String> future
* = executor.submit(new Callable<String>() {
* public String call() {
* return searcher.search(target);
* }});
* 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 <tt>Future</tt> that
* implements <tt>Runnable</tt>, and so may be executed by an <tt>Executor</tt>.
* For example, the above construction with <tt>submit</tt> could be replaced by:
* <pre>
* FutureTask<String> future =
* new FutureTask<String>(new Callable<String>() {
* public String call() {
* return searcher.search(target);
* }});
* 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 <tt>get</tt> method
*/
public interface Future<V> {
/**
* Attempts to cancel execution of this task. This attempt will
* fail if the task has already completed, has already been cancelled,
* or could not be cancelled for some other reason. If successful,
* and this task has not started when <tt>cancel</tt> is called,
* this task should never run. If the task has already started,
* then the <tt>mayInterruptIfRunning</tt> parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task.
*
* <p>After this method returns, subsequent calls to {@link #isDone} will
* always return <tt>true</tt>. Subsequent calls to {@link #isCancelled}
* will always return <tt>true</tt> if this method returned <tt>true</tt>.
*
* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
* task should be interrupted; otherwise, in-progress tasks are allowed
* to complete
* @return <tt>false</tt> if the task could not be cancelled,
* typically because it has already completed normally;
* <tt>true</tt> otherwise
*/
boolean cancel(boolean mayInterruptIfRunning);
/**
* Returns <tt>true</tt> if this task was cancelled before it completed
* normally.
*
* @return <tt>true</tt> if this task was cancelled before it completed
*/
boolean isCancelled();
/**
* Returns <tt>true</tt> if this task completed.
*
* Completion may be due to normal termination, an exception, or
* cancellation -- in all of these cases, this method will return
* <tt>true</tt>.
*
* @return <tt>true</tt> 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;
}