ExecutorServiceCloseable

Class Overview

An Executor ExecutorServiceCloseable that is also AutoCloseable, meaning you can use it in a try with resources statement.

An Executor that provides methods to manage termination and methods that can produce a Future for tracking progress of one or more asynchronous tasks.

An ExecutorService can be shut down, which will cause it to reject new tasks. Two different methods are provided for shutting down an ExecutorService. The shutdown() method will allow previously submitted tasks to execute before terminating, while the 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 ExecutorService should be shut down to allow reclamation of its resources.

Method submit extends base method execute(Runnable) by creating and returning a Future that can be used to cancel execution and/or wait for completion. Methods 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 ExecutorCompletionService can be used to write customized variants of these methods.)

The Executors class provides factory methods for the executor services provided in this package.

Usage Examples

Here is a sketch of a network service in which threads in a thread pool service incoming requests. It uses the preconfigured newFixedThreadPool(int) factory method:

 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
   }
 }
 

The following method shuts down an ExecutorService in two phases, first by calling shutdown to reject incoming tasks, and then calling shutdownNow, if necessary, to cancel any lingering tasks:

 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();
   }
 }
 

Memory consistency effects: Actions in a thread prior to the submission of a Runnable or Callable task to an ExecutorService happen-before any actions taken by that task, which in turn happen-before the result is retrieved via Future.get().

Summary

Public Constructors
	ExecutorServiceCloseable(int iThreadCount, String iThreadPoolName)

Public Methods
boolean	awaitTermination(long timeout, TimeUnit unit)
void	close()
void	execute(Runnable command)
<T> List<Future<T>>	invokeAll(Collection<? extends Callable<T>> tasks)
<T> List<Future<T>>	invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
<T> T	invokeAny(Collection<? extends Callable<T>> tasks)
<T> T	invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
boolean	isShutdown()
boolean	isTerminated()
void	shutdown()
List<Runnable>	shutdownNow()
Future<?>	submit(Runnable task)
<T> Future<T>	submit(Callable<T> task)
<T> Future<T>	submit(Runnable task, T result)

[Expand] Inherited Methods
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait(long arg0, int arg1) final void wait(long arg0) final void wait()
From interface java.lang.AutoCloseable abstract void close()
From interface java.util.concurrent.Executor abstract void execute(Runnable arg0)
From interface java.util.concurrent.ExecutorService abstract boolean awaitTermination(long arg0, TimeUnit arg1) abstract <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> arg0) abstract <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> arg0, long arg1, TimeUnit arg2) abstract <T> T invokeAny(Collection<? extends Callable<T>> arg0) abstract <T> T invokeAny(Collection<? extends Callable<T>> arg0, long arg1, TimeUnit arg2) abstract boolean isShutdown() abstract boolean isTerminated() abstract void shutdown() abstract List<Runnable> shutdownNow() abstract <T> Future<T> submit(Callable<T> arg0) abstract <T> Future<T> submit(Runnable arg0, T arg1) abstract Future<?> submit(Runnable arg0)