| /* |
| * 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 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 {@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 should be interrupted in |
| * an attempt to stop the task. |
| * |
| * <p>After this method returns, subsequent calls to {@link #isDone} will |
| * always return {@code true}. Subsequent calls to {@link #isCancelled} |
| * will always return {@code true} if this method returned {@code true}. |
| * |
| * @param mayInterruptIfRunning {@code true} if the thread executing this |
| * task should be interrupted; otherwise, in-progress tasks are allowed |
| * to complete |
| * @return {@code false} if the task could not be cancelled, |
| * typically because it has already completed normally; |
| * {@code true} otherwise |
| */ |
| 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; |
| } |