/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 *
 * 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;
}