| /* |
| * 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; |
| } |