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+++ b/src/java.base/share/classes/java/util/concurrent/ExecutorService.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,371 @@
+/*
+ * 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;
+
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * An {@link Executor} that provides methods to manage termination and
+ * methods that can produce a {@link Future} for tracking progress of
+ * one or more asynchronous tasks.
+ *
+ * <p>An {@code ExecutorService} can be shut down, which will cause
+ * it to reject new tasks. Two different methods are provided for
+ * shutting down an {@code ExecutorService}. The {@link #shutdown}
+ * method will allow previously submitted tasks to execute before
+ * terminating, while the {@link #shutdownNow} method prevents waiting
+ * tasks from starting and attempts to stop currently executing tasks.
+ * Upon termination, an executor has no tasks actively executing, no
+ * tasks awaiting execution, and no new tasks can be submitted. An
+ * unused {@code ExecutorService} should be shut down to allow
+ * reclamation of its resources.
+ *
+ * <p>Method {@code submit} extends base method {@link
+ * Executor#execute(Runnable)} by creating and returning a {@link Future}
+ * that can be used to cancel execution and/or wait for completion.
+ * Methods {@code invokeAny} and {@code invokeAll} perform the most
+ * commonly useful forms of bulk execution, executing a collection of
+ * tasks and then waiting for at least one, or all, to
+ * complete. (Class {@link ExecutorCompletionService} can be used to
+ * write customized variants of these methods.)
+ *
+ * <p>The {@link Executors} class provides factory methods for the
+ * executor services provided in this package.
+ *
+ * <h3>Usage Examples</h3>
+ *
+ * Here is a sketch of a network service in which threads in a thread
+ * pool service incoming requests. It uses the preconfigured {@link
+ * Executors#newFixedThreadPool} factory method:
+ *
+ * <pre> {@code
+ * class NetworkService implements Runnable {
+ * private final ServerSocket serverSocket;
+ * private final ExecutorService pool;
+ *
+ * public NetworkService(int port, int poolSize)
+ * throws IOException {
+ * serverSocket = new ServerSocket(port);
+ * pool = Executors.newFixedThreadPool(poolSize);
+ * }
+ *
+ * public void run() { // run the service
+ * try {
+ * for (;;) {
+ * pool.execute(new Handler(serverSocket.accept()));
+ * }
+ * } catch (IOException ex) {
+ * pool.shutdown();
+ * }
+ * }
+ * }
+ *
+ * class Handler implements Runnable {
+ * private final Socket socket;
+ * Handler(Socket socket) { this.socket = socket; }
+ * public void run() {
+ * // read and service request on socket
+ * }
+ * }}</pre>
+ *
+ * The following method shuts down an {@code ExecutorService} in two phases,
+ * first by calling {@code shutdown} to reject incoming tasks, and then
+ * calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
+ *
+ * <pre> {@code
+ * void shutdownAndAwaitTermination(ExecutorService pool) {
+ * pool.shutdown(); // Disable new tasks from being submitted
+ * try {
+ * // Wait a while for existing tasks to terminate
+ * if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
+ * pool.shutdownNow(); // Cancel currently executing tasks
+ * // Wait a while for tasks to respond to being cancelled
+ * if (!pool.awaitTermination(60, TimeUnit.SECONDS))
+ * System.err.println("Pool did not terminate");
+ * }
+ * } catch (InterruptedException ie) {
+ * // (Re-)Cancel if current thread also interrupted
+ * pool.shutdownNow();
+ * // Preserve interrupt status
+ * Thread.currentThread().interrupt();
+ * }
+ * }}</pre>
+ *
+ * <p>Memory consistency effects: Actions in a thread prior to the
+ * submission of a {@code Runnable} or {@code Callable} task to an
+ * {@code ExecutorService}
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * any actions taken by that task, which in turn <i>happen-before</i> the
+ * result is retrieved via {@code Future.get()}.
+ *
+ * @since 1.5
+ * @author Doug Lea
+ */
+public interface ExecutorService extends Executor {
+
+ /**
+ * Initiates an orderly shutdown in which previously submitted
+ * tasks are executed, but no new tasks will be accepted.
+ * Invocation has no additional effect if already shut down.
+ *
+ * <p>This method does not wait for previously submitted tasks to
+ * complete execution. Use {@link #awaitTermination awaitTermination}
+ * to do that.
+ *
+ * @throws SecurityException if a security manager exists and
+ * shutting down this ExecutorService may manipulate
+ * threads that the caller is not permitted to modify
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * or the security manager's {@code checkAccess} method
+ * denies access.
+ */
+ void shutdown();
+
+ /**
+ * Attempts to stop all actively executing tasks, halts the
+ * processing of waiting tasks, and returns a list of the tasks
+ * that were awaiting execution.
+ *
+ * <p>This method does not wait for actively executing tasks to
+ * terminate. Use {@link #awaitTermination awaitTermination} to
+ * do that.
+ *
+ * <p>There are no guarantees beyond best-effort attempts to stop
+ * processing actively executing tasks. For example, typical
+ * implementations will cancel via {@link Thread#interrupt}, so any
+ * task that fails to respond to interrupts may never terminate.
+ *
+ * @return list of tasks that never commenced execution
+ * @throws SecurityException if a security manager exists and
+ * shutting down this ExecutorService may manipulate
+ * threads that the caller is not permitted to modify
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")},
+ * or the security manager's {@code checkAccess} method
+ * denies access.
+ */
+ List<Runnable> shutdownNow();
+
+ /**
+ * Returns {@code true} if this executor has been shut down.
+ *
+ * @return {@code true} if this executor has been shut down
+ */
+ boolean isShutdown();
+
+ /**
+ * Returns {@code true} if all tasks have completed following shut down.
+ * Note that {@code isTerminated} is never {@code true} unless
+ * either {@code shutdown} or {@code shutdownNow} was called first.
+ *
+ * @return {@code true} if all tasks have completed following shut down
+ */
+ boolean isTerminated();
+
+ /**
+ * Blocks until all tasks have completed execution after a shutdown
+ * request, or the timeout occurs, or the current thread is
+ * interrupted, whichever happens first.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return {@code true} if this executor terminated and
+ * {@code false} if the timeout elapsed before termination
+ * @throws InterruptedException if interrupted while waiting
+ */
+ boolean awaitTermination(long timeout, TimeUnit unit)
+ throws InterruptedException;
+
+ /**
+ * Submits a value-returning task for execution and returns a
+ * Future representing the pending results of the task. The
+ * Future's {@code get} method will return the task's result upon
+ * successful completion.
+ *
+ * <p>
+ * If you would like to immediately block waiting
+ * for a task, you can use constructions of the form
+ * {@code result = exec.submit(aCallable).get();}
+ *
+ * <p>Note: The {@link Executors} class includes a set of methods
+ * that can convert some other common closure-like objects,
+ * for example, {@link java.security.PrivilegedAction} to
+ * {@link Callable} form so they can be submitted.
+ *
+ * @param task the task to submit
+ * @param <T> the type of the task's result
+ * @return a Future representing pending completion of the task
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ * @throws NullPointerException if the task is null
+ */
+ <T> Future<T> submit(Callable<T> task);
+
+ /**
+ * Submits a Runnable task for execution and returns a Future
+ * representing that task. The Future's {@code get} method will
+ * return the given result upon successful completion.
+ *
+ * @param task the task to submit
+ * @param result the result to return
+ * @param <T> the type of the result
+ * @return a Future representing pending completion of the task
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ * @throws NullPointerException if the task is null
+ */
+ <T> Future<T> submit(Runnable task, T result);
+
+ /**
+ * Submits a Runnable task for execution and returns a Future
+ * representing that task. The Future's {@code get} method will
+ * return {@code null} upon <em>successful</em> completion.
+ *
+ * @param task the task to submit
+ * @return a Future representing pending completion of the task
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ * @throws NullPointerException if the task is null
+ */
+ Future<?> submit(Runnable task);
+
+ /**
+ * Executes the given tasks, returning a list of Futures holding
+ * their status and results when all complete.
+ * {@link Future#isDone} is {@code true} for each
+ * element of the returned list.
+ * Note that a <em>completed</em> task could have
+ * terminated either normally or by throwing an exception.
+ * The results of this method are undefined if the given
+ * collection is modified while this operation is in progress.
+ *
+ * @param tasks the collection of tasks
+ * @param <T> the type of the values returned from the tasks
+ * @return a list of Futures representing the tasks, in the same
+ * sequential order as produced by the iterator for the
+ * given task list, each of which has completed
+ * @throws InterruptedException if interrupted while waiting, in
+ * which case unfinished tasks are cancelled
+ * @throws NullPointerException if tasks or any of its elements are {@code null}
+ * @throws RejectedExecutionException if any task cannot be
+ * scheduled for execution
+ */
+ <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
+ throws InterruptedException;
+
+ /**
+ * Executes the given tasks, returning a list of Futures holding
+ * their status and results
+ * when all complete or the timeout expires, whichever happens first.
+ * {@link Future#isDone} is {@code true} for each
+ * element of the returned list.
+ * Upon return, tasks that have not completed are cancelled.
+ * Note that a <em>completed</em> task could have
+ * terminated either normally or by throwing an exception.
+ * The results of this method are undefined if the given
+ * collection is modified while this operation is in progress.
+ *
+ * @param tasks the collection of tasks
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @param <T> the type of the values returned from the tasks
+ * @return a list of Futures representing the tasks, in the same
+ * sequential order as produced by the iterator for the
+ * given task list. If the operation did not time out,
+ * each task will have completed. If it did time out, some
+ * of these tasks will not have completed.
+ * @throws InterruptedException if interrupted while waiting, in
+ * which case unfinished tasks are cancelled
+ * @throws NullPointerException if tasks, any of its elements, or
+ * unit are {@code null}
+ * @throws RejectedExecutionException if any task cannot be scheduled
+ * for execution
+ */
+ <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
+ long timeout, TimeUnit unit)
+ throws InterruptedException;
+
+ /**
+ * Executes the given tasks, returning the result
+ * of one that has completed successfully (i.e., without throwing
+ * an exception), if any do. Upon normal or exceptional return,
+ * tasks that have not completed are cancelled.
+ * The results of this method are undefined if the given
+ * collection is modified while this operation is in progress.
+ *
+ * @param tasks the collection of tasks
+ * @param <T> the type of the values returned from the tasks
+ * @return the result returned by one of the tasks
+ * @throws InterruptedException if interrupted while waiting
+ * @throws NullPointerException if tasks or any element task
+ * subject to execution is {@code null}
+ * @throws IllegalArgumentException if tasks is empty
+ * @throws ExecutionException if no task successfully completes
+ * @throws RejectedExecutionException if tasks cannot be scheduled
+ * for execution
+ */
+ <T> T invokeAny(Collection<? extends Callable<T>> tasks)
+ throws InterruptedException, ExecutionException;
+
+ /**
+ * Executes the given tasks, returning the result
+ * of one that has completed successfully (i.e., without throwing
+ * an exception), if any do before the given timeout elapses.
+ * Upon normal or exceptional return, tasks that have not
+ * completed are cancelled.
+ * The results of this method are undefined if the given
+ * collection is modified while this operation is in progress.
+ *
+ * @param tasks the collection of tasks
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @param <T> the type of the values returned from the tasks
+ * @return the result returned by one of the tasks
+ * @throws InterruptedException if interrupted while waiting
+ * @throws NullPointerException if tasks, or unit, or any element
+ * task subject to execution is {@code null}
+ * @throws TimeoutException if the given timeout elapses before
+ * any task successfully completes
+ * @throws ExecutionException if no task successfully completes
+ * @throws RejectedExecutionException if tasks cannot be scheduled
+ * for execution
+ */
+ <T> T invokeAny(Collection<? extends Callable<T>> tasks,
+ long timeout, TimeUnit unit)
+ throws InterruptedException, ExecutionException, TimeoutException;
+}