Scala example source code file (ExecutorService.java)

This example Scala source code file (ExecutorService.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

executionexception, executor, executorservice, future, future, interruptedexception, interruptedexception, list, object, object, timeoutexception, timeunit, timeunit, util

The Scala ExecutorService.java source code

/*
 * 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 scala.actors.threadpool;

import scala.actors.threadpool.*; // for javadoc (till 6280605 is fixed)
import java.util.List;
import java.util.Collection;

/**
 * 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 ExecutorService can be shut down, which will cause
 * it to reject new tasks.  Two different methods are provided for
 * shutting down an <tt>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 <tt>ExecutorService should be shut down to allow
 * reclamation of its resources.
 *
 * <p> Method submit extends base method {@link
 * Executor#execute} by creating and returning a {@link Future} that
 * can be used to cancel execution and/or wait for completion.
 * Methods <tt>invokeAny and 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 Example
 *
 * 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>
 * 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 <tt>ExecutorService in two phases,
 * first by calling <tt>shutdown to reject incoming tasks, and then
 * calling <tt>shutdownNow, if necessary, to cancel any lingering tasks:
 *
 * <pre>
 * 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">happen-before
 * any actions taken by that task, which in turn <i>happen-before 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.
     *
     * @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}<tt>("modifyThread"),
     *         or the security manager's <tt>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>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}<tt>("modifyThread"),
     *         or the security manager's <tt>checkAccess method
     *         denies access.
     */
    List shutdownNow();

    /**
     * Returns <tt>true if this executor has been shut down.
     *
     * @return <tt>true if this executor has been shut down
     */
    boolean isShutdown();

    /**
     * Returns <tt>true if all tasks have completed following shut down.
     * Note that <tt>isTerminated is never true unless
     * either <tt>shutdown or shutdownNow was called first.
     *
     * @return <tt>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 <tt>true if this executor terminated and
     *         <tt>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 <tt>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
     * <tt>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
     * @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(Callable task);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's <tt>get method will
     * return the given result upon successful completion.
     *
     * @param task the task to submit
     * @param result the result to return
     * @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, Object result);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's <tt>get method will
     * return <tt>null upon successful 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 <tt>true for each
     * element of the returned list.
     * Note that a <em>completed 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
     * @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 <tt>null
     * @throws RejectedExecutionException if any task cannot be
     *         scheduled for execution
     */

    List invokeAll(Collection 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 <tt>true for each
     * element of the returned list.
     * Upon return, tasks that have not completed are cancelled.
     * Note that a <em>completed 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
     * @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 <tt>null
     * @throws RejectedExecutionException if any task cannot be scheduled
     *         for execution
     */
    List invokeAll(Collection 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
     * @return the result returned by one of the tasks
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks or any of its elements
     *         are <tt>null
     * @throws IllegalArgumentException if tasks is empty
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     *         for execution
     */
    Object invokeAny(Collection 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
     * @return the result returned by one of the tasks.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks, any of its elements, or
     *         unit are <tt>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
     */
    Object invokeAny(Collection tasks, long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}